BIRTH INTERVALS AND HEALTH IN ADULTHOOD: A COMPARISON OF SIBLINGS - - PDF document

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BIRTH INTERVALS AND HEALTH IN ADULTHOOD: A COMPARISON OF SIBLINGS USING SWEDISH REGISTER DATA

KIERON BARCLAY1,2,3 AND MARTIN KOLK2,4,5

1DEPARTMENT OF SOCIAL POLICY, LONDON SCHOOL OF ECONOMICS AND POLITICAL SCIENCE 2DEMOGRAPHY UNIT, DEPARTMENT OF SOCIOLOGY, STOCKHOLM UNIVERSITY 3MAX PLANCK INSTITUTE FOR DEMOGRAPHIC RESEARCH 4CENTRE FOR THE STUDY OF CULTURAL EVOLUTION, STOCKHOLM UNIVERSITY 5INSTITUTE FOR FUTURES STUDIES, STOCKHOLM, SWEDEN

• ABSTRACT. A growing body of research has examined whether birth intervals influence peri-

natal outcomes and child health, as well as long-term educational and socioeconomic outcomes; to date, however, very little research has examined whether birth spacing influences long-term

• health. We use contemporary Swedish population register data to examine the relationship be-

tween birth-to-birth intervals and a variety of health outcomes in adulthood, including height, physical fitness, the probability of falling into different body mass index (BMI) categories, and

• mortality. In models where we do not adjust carefully for family background we find that short

and long birth intervals are clearly associated with height, physical fitness, being overweight or

• bese, and mortality. However, after carefully adjusting for family background using a within-

family sibling comparison design, we find that birth spacing is generally not associated with long-term health, though we find that men born after very long birth intervals have a higher probability of being overweight or obese in early adulthood. Overall we conclude that birth intervals have little independent effect on long-term health outcomes. barclay@demogr.mpg.de | martin.kolk@sociology.su.se

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INTRODUCTION Recent years have seen a resurgence of interest in the long-term consequences of fertility decisions for both the parents and children. Although there have been a large number of stud- ies examining how birth order, family size, and parental age at the time of birth are related to long-term cognitive development, educational and socioeconomic attainment, and health (McLanahan, 2004; Black et al., 2005; Barclay and Kolk, 2015; Barclay and Myrskyl¨ a, 2016; Baranowska-Rataj et al., 2017), the importance of birth spacing for long-term outcomes has received far less attention. Those studies that have studied the medium and long-term impact of birth spacing for children have largely focused upon educational and socioeconomic outcomes (Powell and Steelman, 1990, 1993; Petterson-Lidbom and Skogman Thoursie, 2009; Buckles and Munnich, 2012; Barclay and Kolk, 2017). While there are many studies on the conse- quences of birth spacing for child health, studies on the long-term physical health consequences

• f birth interval length are a rare species (a study using historical data from China by Campbell

and Lee, 2009, is the only example that we are aware of), and to our knowledge this ques- tion has not been examined in a contemporary setting. This is surprising given that previous research has shown that birth interval length is associated with the risk of preterm birth, low birth weight, and child mortality (Conde-Agudelo et al., 2006; DaVanzo et al., 2008), and poor peri-natal outcomes have long-term consequences for socioeconomic attainment (Conley and Bennett, 2000; Black et al., 2007), and health (Leon et al., 1998; Moster et al., 2008; Swamy et al., 2008), even in high-income countries. Furthermore, short intervals may increase sibling competition and dilute the time and resources that parents are able to invest in their children (Blake, 1989; Zajonc, 1976). In this study we use Swedish population register data to examine the relationship between birth interval length and height, physical fitness, and the probability of falling into different body mass index (BMI) categories measured at ages 17 to 20, and mortal- ity over ages 30 to 74. Our study extends the literature on this topic by examining a range of medium- and long-term health outcomes that have not been previously examined in relation to birth spacing, and we do so using a within-family sibling comparison design that allows us to minimise residual confounding and to isolate the net effect of birth interval length on long-term

• health. Furthermore, previous research has focused on the length of the birth interval preceding

the birth of the index person; in this study, we also examine whether the length of the subsequent interval, or the time until the birth of a younger sibling, is associated with long-term health. Empirical Research on Birth Intervals and Health. Although there is a large and growing literature examining the relationship between family background and family structure on long- term health (e.g. Elo and Preston, 1992; Preston et al., 1998; Hayward and Gorman, 2004; McEniry, 2013; Baranowska-Rataj et al., 2017), there has been very little research examining

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THE LONG-TERM HEALTH CONSEQUENCES OF BIRTH INTERVALS 3

the long-term impacts of birth spacing on the health of the children. A study using historical data from Qing China over the period 1749 to 1909 has indicated that a short preceding birth interval of less than 2 years was associated with substantially higher mortality at ages 55-74, and this pattern persists even when comparing siblings within the same family (Campbell and Lee, 2009). There is also some preliminary evidence that short birth intervals may be associated with an increased risk of schizophrenia (Smits et al., 2004; Gunawardana et al., 2011), autism (Gunnes et al., 2013), and self-harm (Riordan et al., 2012), but few other studies have pursued this topic. In contrast to the research on the long-term health impacts of birth intervals, there is a volu- minous literature on the short-term health impacts of birth spacing on child and maternal health. Hundreds of studies using data from high-income countries in North America and Western Eu- rope, as well as low-income countries, have shown that short birth intervals, variously classified as less than 6, 7, 9 or 24 months, are associated with an increased risk of low birth weight, preterm birth, intrauterine growth restriction (IUGR), and and being small for gestational age (SGA) (Conde-Agudelo et al., 2006). Some research in high-income countries also suggests that long birth intervals are associated with an increased risk of fetal death, neonatal mortality, and infant mortality(Stephansson et al., 2003; Hussaini et al., 2013; McKinney et al., 2017), but the evidence for an increased risk of mortality is clearer in low-income countries (Fortney and Higgins, 1984; Casterline, 1989; Huttly et al., 1992; Smith et al., 2003; Rutstein, 2005; Conde-Agudelo et al., 2005). A meta-analysis of studies using data from both low- and high- income countries published up to 2006 showed that there is a J-shaped curve in the relationship between the length of birth intervals and peri-natal and child health outcomes; interpregnancy intervals shorter than 18 months, and longer than 59 months are significantly associated with poor perinatal outcomes (Conde-Agudelo et al., 2006). As a consequence, the World Health Organization (WHO) has issued recommendations for mothers wait at least 24 months before attempting to conceive again (WHO, 2005). Despite this almost overwhelming body of evidence, a pair of recent studies have cast doubt

• n whether the length of birth intervals is causally responsible for poor peri-natal outcomes

in high-income countries (Klebanoff, 2017). Analyses using data from Australia (Ball et al., 2014) and Canada (Hanley et al., 2017), have shown that when comparing siblings born to the same mother, the association between short birth spacing and the risk of preterm birth, low birth weight, and SGA is either completely removed, or substantially reduced. However, another pair

• f recent studies that also used a sibling-comparison design find that the association between

short intervals and an increased risk of preterm birth and low birth weight persisted (Shachar et al., 2016; Koullali et al., 2016). Partly in response to these new findings, a 2015 report from the Centers for Disease Control and Prevention (CDC) in the United States suggested that

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more research is needed to understand the impact of birth spacing on maternal and child health (Copen et al., 2015). Birth Intervals and Long-term Health: Potential Explanatory Processes. A previous re- view of potential explanatory mechanisms for a causal relationship between birth interval length and child health outcomes identified eight candidates: maternal nutrient depletion, folate deple- tion, cervical insufficiency, vertical transmission of infections, suboptimal lactation related to breastfeeding-pregnancy overlap, physiological regression, sibling competition, and transmis- sion of infectious diseases amongst siblings (Conde-Agudelo et al., 2012). The first six can be broadly categorised as physiological explanations related to prenatal conditions, while the latter two are better categorised in reference to social and environmental conditions within the family and household. A further important factor is the role of confounding and selection processes. In the following sections we consider each of these three groups of explanations in turn, and discuss the processes by which each might be linked to the long-run health outcomes that we study in this outcome: height, physical fitness, BMI, and mortality. Physiological Mechanisms. The maternal nutrient depletion hypothesis, in relation to birth in- tervals, describes how the health of the mother as well as the foetus can be affected if the mother suffers from nutrient depletion due to a short interval between pregnancies (Winkvist et al., 1992; King, 2003). Essentially a short birth interval, and post-partum activities such as breastfeeding, mean that the mother may not have completed the process of nutrient repletion, and this can lead to competition between the mother and foetus for resources, thereby affecting foetal growth. The folate depletion hypothesis is very similar, but applies specifically to the maternal repletion of folic acid, which is critical for foetal growth (Smits and Essed, 2001). The cervical insufficiency hypothesis describes how insufficient time between pregnancies can mean that muscles in the reproductive tissues do not fully recover, limiting the physical ability of the mother to retain the pregnancy (Haaga, 1988). Structural weaknesses in the cervix can lead to preterm birth (Ludmir and Sehdev, 2000). The vertical transmission of infections hypothesis concerns how pregnant women can attract infections during the pregnancy, which may continue to survive in or on their bodies for a limited period of time after giving birth (Goldenberg et al., 2005), increasing the risk of exposure for a foetus conceived after a short interval. These per- sistent maternal infections may be located in a physical region whereby the new foetus can be directly infected, or cause an infection that leads to preterm delivery (Cheng et al., 2008). These hypotheses primarily predict poor outcomes for the pregnancy following a short birth interval. The breastfeeding-pregnancy overlap hypothesis describes how continued breastfeeding dur- ing a subsequent pregnancy, relatively uncommon, due to lactational amenorrhea (Trussell, 2004), but not impossible, can lead to lower quality breastmilk due to the competing demands on

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the mother’s physical resources. However, this behaviour is probably very uncommon in Swe-

• den. Breastfeeding-pregnancy overlap would primarily affect the older child whose younger

sibling was conceived after a short interval. The physiological regression hypothesis has been proposed to explain why relatively long birth intervals, greater than 5 years, are also associated with worse peri-natal outcomes (Zhu et al., 1999). Pregnancy is associated with a number of physical changes in the female body, which first occur during the first pregnancy a woman expe-

• riences. A long birth interval may lead to a physical ‘regression’ to a state where the body is no

longer primed for childbearing. It has been suggested that this is why peri-natal outcomes for children born after long birth intervals are similarly poor to peri-natal outcomes for first-born children. Reviewing the evidence, Conde-Agudelo et al. (2012) assessed that there is indirect, though not direct, evidence to support the maternal depletion and physiological regression hypothe- ses, growing evidence to support the folate depletion hypothesis, emerging evidence to support the vertical transmission of infections and cervical insufficiency hypotheses, and only limited evidence to support the breastfeeding-pregnancy overlap hypothesis. In this study we examine health outcomes in adulthood rather than childhood, but a growing number of studies have linked peri-natal outcomes to long-term health. Low birth weight and and preterm birth are associated with an increased risk of cardiovascular disease in adulthood (Frankel et al., 1996; Rich-Edwards et al., 1997; Leon et al., 1998), mental and physical disabil- ity (Moster et al., 2008), higher mortality, lower fertility (Swamy et al., 2008), and lower height, IQ, and educational and socioeconomic attainment (Conley and Bennett, 2000; Behrman and Rosenzweig, 2004; Black et al., 2007; Derraik et al., 2017). Behrman and Rosenzweig (2004) report that birth weight is not associated with BMI, but other work has shown that preterm birth is associated with altered adiposity (Uthaya et al., 2005). Children born with low birth weight experience accelerated weight gain during infancy, and studies suggest that this may be linked to an increased risk of being overweight or obese in adulthood (Mathai et al., 2013), as well as a higher risk cardiovascular health profile (Posod et al., 2016). Since short birth intervals are also associated with worse maternal health (Conde-Agudelo et al., 2007), it is also possible that birth interval length affects the long-term health of the child through a negative impact on the health, and perhaps subsequently socioeconomic status, of the mother. Social and Environmental Mechanisms. Birth interval length may also influence social and environmental conditions during childhood, by diluting parental resources, and by affecting in- teraction dynamics between siblings. The sibling competition, or resource dilution, hypothesis (Blake, 1989) can be applied to birth spacing when one considers how short intervals mean that parental resources are split amongst their children, particularly during the earliest years of life,

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which recent research suggests may be a particularly sensitive development period (Campbell and Ramey, 1994; Campbell et al., 2001; Heckman, 2006; Knudsen et al., 2006). Even though the dilution of socioeconomic resources may not have a large impact in Sweden given the high level of human development, comprehensive welfare state, and extensive parental leave system, parental time is absolutely finite. There is some preliminary evidence that short birth intervals lead to less parental supervision in disadvantaged families (Crowne et al., 2012), and that in- tervals shorter than two years are associated with an increased risk of injuries amongst children (Nathens et al., 2000). Another potentially important theory here is the confluence hypothesis (Zajonc and Markus, 1975), which argues that short birth intervals mean that the average degree of intellectual stimu- lation in the household is more rapidly lowered by the arrival of an additional child. Thus, short birth intervals mean less time interacting with your cognitively mature parents, and more time interacting with your callow siblings. These processes could lead indirectly to worse health in adulthood by negatively affecting cognitive development and educational and socioeconomic achievement. The transmission of infectious disease hypothesis argues that the younger of any pair of sib- lings will be more exposed to infectious diseases than they would be without an older sibling, and particularly if the older sibling is roughly two years older - a common birth interval length, and an age where the older sibling is commonly carrying an infection (Conde-Agudelo et al., 2012). Alternatively, however, a theory dubbed the hygiene hypothesis has been proposed to ex- plain why children from larger families are less likely to develop allergies as early life exposure to disease can strengthen the capacities of the immune system (Strachan, 1989; Karmaus and Botezan, 2002). Indeed, in a high-income country like Sweden where disease exposure during childhood is rarely severe or life threatening, the more common mild respiratory infections that children experience may help to strengthen the immune system. Thus, the transmission of mild infectious diseases might be beneficial for long-term health rather than harmful. Selection and Confounding. While the hypothetical mechanisms linking birth intervals to long- term health that we have reviewed above assume that there is a genuine causal relationship, an alternative, non-causal, explanation is that any crude association between birth interval length and long-term health might be explained by confounding by factors related to the timing and spacing of births as well as child health. Such confounding factors might include maternal health, or parental education and socioeconomic conditions. If, for example, especially short or long birth intervals were more common amongst parents with low education or worse health, this could explain a negative association between birth interval length and long-term child

• health. For example, in the United States, interpregnancy intervals less than 18 months are

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more likely to be reported as mistimed or unwanted, but amongst those who did report short intervals, those who were older, more highly educated, and married were more likely to re- port them as intentional (Gemmill and Lindberg, 2013). The latter pattern seems to reflect a later age at first birth and an accelerated fertility schedule designed to achieve desired family size (Gemmill and Lindberg, 2013). Nevertheless, despite socioeconomic advantage, multiple closely spaced births amongst mothers of advanced reproductive age may exacerbate the harm- ful impact of the physiological mechanisms described above. Other factors, such as underlying maternal health, are more difficult to observe, and may also be associated with birth interval

• length. For example, a woman who has difficult getting pregnant because of an underlying

health issue will be more likely to have longer birth intervals; in turn, her health might affect her childrearing, or her children might inherit her health problems. It is difficult a priori to assess the extent to which previously research on birth spacing may have been affected by omitted variable bias. However, recent studies that have examined the association between birth interval length and both short- and long-term outcomes amongst sib- lings born to the same mother suggest that this may indeed be a prevalent issue. By comparing sibling born to the same mother it is possible to adjust for all factors that are shared amongst siblings but which might otherwise be difficult to observe and adjust for, such as maternal and paternal health, shared genetics, and unmeasured socioeconomic aspects of the shared home

• environment. As described above in the section on previous empirical research, several recent

studies have shown that after comparing siblings, the relationship between birth interval length and the risk of poor peri-natal outcomes such as preterm birth, low birth weight, and SGA is either completely removed, or reduced very substantially (Ball et al., 2014; Shachar et al., 2016; Hanley et al., 2017). Furthermore, another recent study has shown that when adopting the same approach, the negative effect of short birth spacing on medium- and long-term educational, cognitive, and socioeconomic outcomes, previously widely reported (e.g. Powell and Steelman, 1990, 1993; Buckles and Munnich, 2012), is also wiped out (Barclay and Kolk, 2017). Based upon the existing body of evidence, there are good reasons to believe that birth inter- vals should be related to long-term health outcomes, while a number of recent studies suggest that this association may be primarily driven by selection and confounding. In this study we apply a sibling fixed effects approach to assess the relationship between birth interval length and long-term health. DATA, AND METHODS

• Data. This study uses administrative register data on the full population of Sweden. Each indi-

vidual in Sweden has a unique personal identification number (PIN) that is universally used for administrative purposes. A key administrative register that we use in this study is the Swedish

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multigenerational register, which allows us to link individuals to their parents and siblings. We examine sibling groups where all of the children were born in Sweden in order to maximise the accuracy of the parent-child-sibling linkages. In this study we examine the relationship between birth intervals and five different outcome variables, which are height, physical fitness, being overweight or obese, being underweight or severely underweight, and mortality. Apart from mortality, information on all of the other out- come variables are drawn from the Swedish military conscription register. In Sweden men were universally required to report to military conscription tests between ages 17 to 20 to determine their physical and psychological suitability for military service. Data on height, physical fit- ness, and BMI are available for cohorts born 1962-1979. Only men were required to report to conscription tests in Sweden, so we do not have data on these measures for women. However, although the outcome measures are only available for men, the measures of birth spacing and

• ther characteristics of the sibling group are based upon the whole sibling groups, including

males and females. The other main register that we use is the Swedish mortality register, which contains detailed information on all deaths in Sweden between 1960 and 2012. Although the Swedish mortality register contains data over the period 1960 to 2012, the multigenerational registers that allow family members to be linked to one another are incomplete before the 1990s (SCB, 2011). In this study we focus on all-cause mortality over the period 1990-2012. We study mortality for Swedish men and women born 1938 to 1960. This means that we study mortality over the age range 52 to 74 for those born in 1938, and over the age range 30 to 54 for those born in 1960. This study is based upon a population of sibling groups where neither parent have any chil- dren with a third partner. This means that none of the individuals included in our analysis have any half-siblings. Although this reduces external validity, there are also distinct advantages such as increasing the degree of genetic similarity of the siblings, and increasing the likelihood that the children share the same childhood environment. We also exclude sibling groups with multiple births as it is not possible to distinguish the impact of birth interval from the presence

• f a twin on long-term outcomes in these families.

In our analyses we compare the results from within-family sibling fixed effect models and between-family linear regression models. We explain those models in detail in the following ‘Statistical Analyses’ section, but this modelling approach also has implications for our data

• selection. As the fixed effect approach requires variance in the groups in which the comparisons

are conducted, we necessarily exclude sibling groups with only one child, as well as sibling groups with two children, as these sibling groups only contain one birth interval. In studying the impact of birth intervals on each of the six outcomes that we address, we perform separate analyses examining the importance of the length of the preceding birth interval

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5 10 15 Percent 6

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6 > 9 6 Preceding Birth Interval

(a) Preceding Birth Interval

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(b) Subsequent Birth Interval

FIGURE 1. Birth Interval (months) Distribution in Sweden, 1938-1979. (the time in months between the birth of the older sibling and the birth of the index person), and the subsequent birth interval (the time in months between the birth of the index person and the birth of the younger sibling). In the analyses examining the importance of the preceding birth interval, we necessarily exclude first-born individuals, as there was no preceding interval. So

• ur analysis population for the analyses on the preceding birth interval is second and later-born

children in sibling groups with at least three children. In our analyses examining the importance

• f the subsequent birth interval, we necessarily exclude last-born individuals, as they do not

have any sibling born after them. Table S1, in the Supplementary Information, details how we reach our analytical sample. The measure for the birth interval that we use in this study is the length of the birth-to-birth interval, meaning the period of time in months from one live birth to another. We categorise the length of the birth interval into 16 different categories, which are 6 month periods from a min- imum of 6 months to 96 months or longer. In our analyses we choose a reference category for the preceding and subsequent birth interval of 25-30 months. The distribution of birth intervals in Sweden between 1938 and 1979 is shown in Figure 1. Outcome Variables.

• Height. Height is measured in centimetres. For our analyses we standardise height.

Physical Fitness. Our measure for physical fitness is based upon a measure of maximal working capacity, measured in watts (fysisk arbetsf¨

• rm˚

aga i watt). Maximal working capacity (MWC) is measured as the maximum resistance attained in watts when riding on a stationary bike during a time period of 5 to 10 minutes, and is closely related to maximal oxygen uptake (V02max), also known as maximal aerobic capacity. The correlation between these two variables has been

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reported in the literature as approximately 0.9 (Patton et al., 1982). The variable for MWC has been found to be an important predictor of mortality in adulthood amongst men (Sandvik et al., 1993). A stationary bike is one of the most effective ways of measuring aerobic fitness. Since a measure of MWC in watts is not intuitively easy to interpret, we standardise this outcome measure. BMI Categories. We use measures of height and weight to calculate body mass index (BMI)1 at the time of conscription test. Using the standard cutoff points we categorise BMI into over- weight or obese (25), normal (18.5-25), and underweight or severely underweight (18.5).

• Mortality. We study all-cause mortality for Swedish men and women born 1938 to 1960 over

the period 1990-2012. This means that, conditional upon survival to 1990, we study mortality

• ver the age range 52 to 74 for those born in 1938, and over the age range 30 to 54 for those

born in 1960.

• Covariates. In addition to our main explanatory variable, the length of birth intervals, we in-

clude several covariates in our models that are likely to be associated with both birth spacing as well as long-term health. Factors such as birth order, parental age at the time of birth, and birth year may be associated with birth interval length, and are also associated with long-term health outcomes. We include controls for birth order as both the confluence hypothesis and the resource dilution hypothesis predict independent effects of birth order and birth spacing, and previous research has indicated that birth order is related to height (Myrskyl¨ a, Silventoinen, Jelenkovic, Tynelius and Rasmussen, 2013), physical fitness (Barclay and Myrskyl¨ a, 2014), BMI (Jelenkovic et al., 2013), and mortality (Barclay and Kolk, 2015). Birth interval length is also likely to be associated with maternal age, and maternal age is associated with adult height (Myrskyl¨ a, Silventoinen, Tynelius and Rasmussen, 2013), physical fitness (Barclay and Myrskyl¨ a, 2016), and mortality (Smith et al., 2009). We adjust for maternal age using five-year

• categories. Previous studies have also shown that there are secular trends in height, obesity, and

mortality, with people becoming taller (Komlos and Lauderdale, 2007), heavier (Lissner et al., 2000), and living longer (Oeppen and Vaupel, 2002), so we also adjust our analyses for birth

• year. For the analyses drawn from the military conscription register we also adjust for age at

the time of conscription test, and the year of the conscription test. Statistical Analyses.

1BMI = masskg height2

m

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Military Conscription Data. To study the relationship between birth intervals and the four out- come variables drawn from the military conscription register, described above, we use fixed effects linear regression. Our outcome variables for physical fitness and height are continuous, but we study categorisation of being overweight or obese, and underweight or severely under- weight, as binary variables, treating each outcome as though it were independent. In these cases we also use linear regression, as a linear probability model using robust standard errors. The fixed effects are applied to the sibling group, meaning that we conduct a within-family

• comparison. The use of sibling fixed effects implicitly adjusts for all factors that remain constant

within the sibling group. This means that the within-family comparison adjusts for the size of the sibling group, as well as parental resources, to the degree that the latter remains constant. The fixed effects approach also inherently adjusts for factors that are difficult to observe and measure, such as all elements of shared socioeconomic background and general parenting style, to the extent that such factors are indeed shared by siblings. For each outcome variable we estimate four different models: one between-family compari- son and one within-family comparison examining the relationship between the preceding birth interval and the outcome variable, and one between-family comparison and one within-family comparison examining the relationship between the subsequent birth interval and the outcome variable, using a different population for the analyses on the preceding and subsequent intervals:

yi = β1PBIi +β2BirthOrderi +β3MatAgei +β4BirthYeari +β5ConAgei +β6ConYeari +β7Sizei +α +εi (1) yi j = β1PBIi j +β2BirthOrderi j +β3MatAgei j +β4BirthYeari j +β5ConAgei j +β6ConYeari j +α j +εi j (2) yi = β1SBIi +β2BirthOrderi +β3MatAgei +β4BirthYeari +β5ConAgei +β6ConYeari +β7Sizei +α +εi (3) yi j = β1SBIi j +β2BirthOrderi j +β3MatAgei j +β4BirthYeari j +β5ConAgei j +β6ConYeari j +α j +εi j (4)

where yij is the outcome for individual i in sibling group j on height, physical fitness, being

• verweight or obese, and underweight or severely underweight. In Model 1 we use a regular

linear regression, meaning a between-family comparison, to examine the relationship between PBIi, the length of the preceding birth interval, and control for birth order, maternal age, birth year, age at the time of the conscription test, year of the conscription test, and sibling group size. PBIi is entered into the model as a series of 16 dummy variables based on 6-month categories for the length of the preceding birth interval. In Model 1 our analysis population is second and later-born children in sibling groups with at least three children, meaning that we exclude first- borns as they have no value for the length of the preceding interval. In Model 2 we introduce the sibling fixed effect αj, and remove the control for sibling group size as that is adjusted for in

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the fixed effect approach. We use the sample analysis sample for Model 2 as that used in Model

• 1. Models 3 and 4 follow the same format, except we substitute the variable for the preceding

interval with SBI, a variable for the length of the subsequent interval. We regard Models 2 and 4 as an improvement on Models 1 and 3, respectively, as the sibling comparison approach that we use in Models 2 and 4 minimises residual confounding from unobserved factors that are shared by siblings. To this end we are much better able to isolate the net effect of birth intervals on the multiple long-term outcomes that we study. Mortality Data. To study mortality, we use survival analysis in the form of Cox proportional hazard regressions (Cox, 1972). The proportional hazards model is expressed as: h(t|X1,...,Xk) = h0(t) exp

• k

∑

j=1

βjXj(t)

• (5)

where h(t|X1,...,Xk) is the hazard rate for individuals with characteristics X1,...,Xk at time t, h0(t) is the baseline hazard at time t, and β j, j = 1,...,k are the estimated coefficients. Since the failure event in our analysis is the death of the individual, the baseline hazard of our model, h0(t), is age. Individuals are censored on first migration out of Sweden, at death, or in 2012; whichever comes first. To estimate a sibling comparison model we used stratified Cox models (Allison, 2009), stratified by the shared sibling group ID. The stratified Cox model takes the following form, where the hazard for an individual from stratum s is: hs(t|X1,...,Xk) = h0s(t) exp

• k

∑

j=1

βjXj(t)

• (6)

where h0s(t) is the baseline hazard for stratum s, s = 1,...,S. Each stratum, s, is a sibling

• group. In the standard Cox proportional hazard regression the baseline hazard h0 is common to

all individuals in the analysis. In the stratified Cox model, above, we allow the baseline hazard to differ between strata, based upon the assumption that there are unobserved factors particular to each sibling group that may confound the relationship between birth intervals and mortality in adulthood (Allison, 2009, chapter 5). As with the fixed effects approach applied to linear regression, these stratified Cox models adjust for all factors that are shared by siblings. We estimate the following models:

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logh(t) = β1PBIi +β2Sexi +β3BirthOrderi +β4MatAgei +β5BirthYeari +β6Sizei (7) logh(t) = β1PBIij +β2Sexij +β3BirthOrderij +β4MatAgeij +β5BirthYearij +α j (8) logh(t) = β1SBIi +β2Sexi +β3BirthOrderi +β4MatAgei +β5BirthYeari +β6Sizei (9) logh(t) = β1SBIij +β2Sexij +β3BirthOrderij +β4MatAgeij +β5BirthYearij +α j (10) where loghi(t) is the log hazard of mortality, α j is the fixed effect for sibling group j, and the index ij refers to the individual i in sibling group j. As with the linear regression analyses, PBIi is entered into the model as a series of 16 dummy variables based on 6-month categories for the length of the preceding birth interval. In Model 7 our analysis population is second and later-born children in sibling groups with at least three children, meaning that we exclude first- borns as they have no value for the length of the preceding interval. In Model 8 we introduce the sibling fixed effect αj, and remove the control for sibling group size as that is implicitly adjusted for. We use the sample analysis sample for Model 7 as that used in Model 6. In Models 9 and 10 we substitute the variable for the preceding interval with SBIi, a variable for the length

• f the subsequent interval. We regard Models 8 and 10 as an improvement on Models 7 and

9, respectively, as the stratified approach that we use in Models 8 and 10 minimises residual confounding from unobserved factors that are shared by siblings. RESULTS

• Descriptives. Table 1 displays summary statistics for the five outcomes variables that we study.

For physical fitness, height, being underweight or severely underweight, and being overweight

• r obese, we show the mean by categories of birth interval length in our analytical samples. For

mortality we show the number of deaths by birth interval length as well as the rate of mortality. For physical fitness we can see that those born before or after intervals of 25-36 months have the highest scores while both shorter and longer intervals are associated with lower fitness. For height we observe the same pattern by the length of the subsequent interval, but there appears to be little variation by the length of the preceding interval. Being underweight is less common at tail ends of the birth interval distribution, while the percentage of overweight individuals is higher amongst those born after a long preceding birth interval. Mortality rates are lower amongst those born after a long interval, but higher amongst those born before a long interval. More detailed descriptive information can be found in the Supplementary Information, in Tables S2 to S5.

• Height. The results for the relationship between birth interval length and height standardised

can be seen in Figure 2. One standard deviation for height in 6.5cm. The full tables of the

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TABLE 1. Summary Statistics: Mean of the Outcome Variables by the Length

• f Preceding and Subsequent Birth Intervals in Months.

Physical Fitness (watts) Height (cm) Underweight (%) Interval Preceding Subsequent Preceding Subsequent Preceding Subsequent 6-12 295.1 294.4 178.8 178.6 6.4 6.8 13-18 297.0 298.5 179.3 179.4 7.5 7.2 19-24 299.6 301.7 179.5 179.8 6.5 7.3 25-30 301.4 302.2 179.5 179.6 6.8 7.1 31-36 300.9 302.3 179.5 179.6 6.9 7.1 37-42 299.9 301.5 179.5 179.5 7.1 7.3 43-48 299.0 302.4 179.5 179.6 6.4 7.3 49-54 299.1 301.4 179.6 179.5 7.3 7.0 55-60 298.3 299.8 179.5 179.5 6.7 7.0 61-66 298.6 301.5 179.5 179.4 5.9 6.8 67-72 298.9 300.8 179.7 179.4 7.3 6.7 73-78 299.1 302.3 179.6 179.4 7.9 6.1 79-84 298.1 301.5 179.4 179.3 6.7 6.6 85-90 297.8 299.5 179.6 179.5 6.1 7.4 91-96 299.4 299.4 179.9 179.1 4.5 6.5 97+ 297.5 299.7 179.5 179.3 6.0 6.3 All 299.4 301.2 179.5 179.5 6.8 7.0 Overweight (%) Mortality Rate (10−3) Number of Deaths Interval Preceding Subsequent Preceding Subsequent Preceding Subsequent 6-12 9.5 11.7 1.22 1.25 659 624 13-18 10.2 10.9 1.20 1.32 6,322 6,352 19-24 9.9 10.3 1.18 1.37 7,366 7,658 25-30 9.8 10.8 1.25 1.41 6,230 6,287 31-36 11.0 10.5 1.23 1.46 5,038 5,374 37-42 11.0 10.9 1.24 1.49 3,982 4,337 43-48 11.3 10.8 1.21 1.56 3,269 3,758 49-54 11.5 11.2 1.22 1.52 2,586 2,943 55-60 13.0 10.7 1.12 1.60 2,041 2,606 61-66 13.2 10.8 1.16 1.61 1,659 2,125 67-72 13.9 10.3 1.16 1.59 1,349 1,689 73-78 14.1 11.4 1.09 1.58 1,026 1,398 79-84 15.3 10.4 1.06 1.64 822 1,215 85-90 15.4 11.3 1.00 1.66 596 980 91-96 17.1 10.8 0.95 1.63 477 843 97+ 18.0 11.1 0.84 1.68 1,635 3,820 All 11.5 10.8 1.18 1.47 45,057 52,009

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FIGURE 2. Height at ages 17 to 20 by preceding and subsequent birth intervals, Swedish men born 1962 to 1979. The analysis population for examining pre- ceding birth intervals consists of individuals in sibling groups with at least three male children, excluding the first-born. The analysis population for examining subsequent birth intervals consists of individuals in sibling groups with at least three male children, excluding the last-born. Error bars are 95% confidence in- tervals. results can be found in the Supplementary Information in Tables S6 and S7. The results for the length of the preceding birth interval can be seen in the left panel, and the results for the length

• f the subsequent interval can be seen in right panel. As can be seen, short preceding birth

intervals are not significantly associated with height in the between-family comparison model, but longer birth intervals are associated with lower height. Individuals born after an interval of 61-66 are 5% of a standard deviation shorter than those born after intervals of 25-30 months, while those born after intervals of 96 months or longer are 11% of a standard deviation shorter than the reference category. However, the results from the sibling comparison model show that there are no statistically significant differences in height by birth interval length.

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FIGURE 3. Physical fitness at ages 17 to 20 by preceding and subsequent birth intervals, Swedish men born 1962 to 1979. The analysis population for exam- ining preceding birth intervals consists of individuals in sibling groups with at least three male children, excluding the first-born. The analysis population for examining subsequent birth intervals consists of individuals in sibling groups with at least three male children, excluding the last-born. Error bars are 95% confidence intervals. The between-family analysis estimates for the association between the length of the subse- quent birth interval and height, in the right panel, show that individuals who experienced the birth of a sibling shortly after their own birth are estimated to be shorter. When the subsequent birth interval length was only 6-12 months, then individuals were 10% of a standard deviation shorter than if the birth interval had been 25-30 months. However, the within-family compar- ison analysis again suggests that this association may have been driven by unobserved factors associated with the timing and spacing of births as well as long-term health. In the sibling com- parison analysis there are no statistically significant associations between the subsequent birth interval length and height.

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Physical Fitness. The results for the relationship between birth interval length and physical fitness can be seen in Figure 3. The full tables of the results can be found in the Supplementary Information in Tables S8 and S9. The between-family analyses in the left panel show that being born after a long birth interval is associated with substantially lower physical fitness. Indeed, those born after an interval of 96 months or longer have a maximal working capacity that is also 20% of a standard deviation lower than the reference category. In general the results from the within-family comparison analysis do not show a particularly clear pattern in the association, but there is some indication that being born after a birth interval length of 31-54 months, and being born after a birth interval of 13-24 months, decreases physical fitness by about 5% of a standard deviation in comparison to the reference category of 25-30 months. The results for the relationship between the length of the subsequent interval and physical fitness are shown in the right panel. The between-family analyses generally show that there is no statistically significant relationship, but a very short subsequent interval of 6-12 months is associated with having a maximal working capacity 7% of a standard deviation lower. The re- sults from the within-family comparison, however, indicate that neither a very short subsequent interval nor any other subsequent interval length are associated with differences in physical fitness in early adulthood. Overweight or Obese. The results for the probability of being overweight or obese are shown in Figure 4. The full tables of the results can be found in the Supplementary Information in Tables S10 and S11. Since these analyses were conducted using linear probability models the y-axis shows the predicted probability of high BMI in relation to birth interval length. The results for the length of the preceding interval, shown in the left panel of Figure 4, indicate that being born after an interval of 31 months or longer is associated with a greater probability of being overweight or obese in early adulthood, and this probability increases the longer the birth interval was. In this case, we find that the results from the within-family sibling comparison model are relatively consistent with the results from the between-family comparison model. The results for the association between the subsequent interval length and the predicted probability

• f being overweight or obese are shown in the right panel of Figure 4. Both the between-

family and within-family comparison analyses indicate that there are no statistically significant associations between subsequent interval length and the probability of being overweight or

• bese in early adulthood.

Underweight or Severely Underweight. The estimates for the relationship between birth in- terval length and the predicted probability of being underweight or severely underweight can be seen in Figure 5. The full tables of the results can be found in the Supplementary Information in Tables S12 and S13. Being underweight or severely underweight is less common than being

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FIGURE 4. Predicted probability of being overweight or obese by preceding and subsequent birth intervals, Swedish men born 1962 to 1979. The analysis pop- ulation for examining preceding birth intervals consists of individuals in sibling groups with at least three male children, excluding the first-born. The analysis population for examining subsequent birth intervals consists of individuals in sibling groups with at least three male children, excluding the last-born. Error bars are 95% confidence intervals.

• verweight or obese in our data, which is unsurprising given that our data is based on males aged

17-20, and we find few clear patterns in the association between birth interval lengths and being underweight or severely underweight. This applies to both the length of the preceding and the subsequent birth interval. The only statistically significant pattern that can be observed is that the between-family estimates indicate that those born after a long birth interval of 91 months or longer are less likely to be underweight. However, the association between birth interval length and the probability of being underweight is not visible in the within-family comparison model that adjusts for factors shared by siblings.

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FIGURE 5. Predicted probability of being underweight by preceding and subse- quent birth intervals, Swedish men born 1962 to 1979. The analysis population for examining preceding birth intervals consists of individuals in sibling groups with at least three male children, excluding the first-born. The analysis popu- lation for examining subsequent birth intervals consists of individuals in sibling groups with at least three male children, excluding the last-born. Error bars are 95% confidence intervals.

• Mortality. Finally, the results for the association between birth interval length and the hazard
• f mortality in adulthood are shown in Figure 6. The full tables of the results can be found in

the Supplementary Information in Tables S14 and S15. The between-family analysis presented in the left panel, showing the risk of mortality in relation to the length of the preceding interval, indicates that those born after a short birth interval, or a particularly long birth interval of 91 months or longer, have lower mortality than those born after an interval of 25-30 months. This is somewhat surprising given that previous research has typically indicated that short and long birth intervals are likely to have negative consequences. However, in the within-family compar- ison model we find that the length of the preceding birth interval is not significantly associated

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FIGURE 6. Hazard of mortality by preceding and subsequent birth intervals, Swedish men and women born 1938 to 1960. The analysis population for exam- ining preceding birth intervals consists of individuals in sibling groups with at least three children, excluding the first-born. The analysis population for exam- ining subsequent birth intervals consists of individuals in sibling groups with at least three children, excluding the last-born. Error bars are 95% confidence in- tervals. with the hazard of mortality in adulthood. The results in the right hand panel, for the length of the subsequent interval, are far more pronounced. The results from the between-family analysis show that a longer subsequent birth interval is almost monotonically associated with a greater hazard of mortality in adulthood. Again, however, in the within-family comparison model, which adjusts for factors unobserved but shared by siblings, there is no statistically significant relationship between subsequent birth interval length and mortality in adulthood, though the point estimates may indicate a higher hazard for the longest birth intervals. Robustness Checks. We have also conducted a series of robustness checks using different op- erationalizations of the birth interval length to examine whether this produces different results.

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We have re-run our models using two different binary specifications for the length of the pre- ceding and subsequent birth interval, indicating whether the interval was 18 months or longer,

• r 24 months or longer, and in the within-family comparison models we find no statistically sig-

nificant effects of birth interval length on long-term outcomes. We have also run our analyses using linear and quadratic terms for birth interval length, and again find that when comparing siblings who share the same biological mother and father, birth interval length does not have a significant effect on long-term health outcomes. Those results can be seen in the Supplementary Information, in Tables S16 and S17. For our analyses of mortality we have also investigated whether there is a significant interaction between gender and birth interval length, but we found no statistically significant differences. DISCUSSION In this study we are one of the first to examine the relationship between birth interval length and long-term health outcomes. Although a previous study using historical data has shown that a preceding birth interval shorter than two years was associated with substantially higher mor- tality at ages 55 to 74 (Campbell and Lee, 2009), we are not aware of other research examining how birth interval length is related to long-term physical health in contemporary populations. When reducing residual confounding as much as possible by comparing siblings who share the same biological parents, we found that birth interval length was not significantly associated with height, physical fitness, or the probability of being underweight or severely underweight amongst men, or mortality amongst men and women. However, we did find some evidence to suggest that a long preceding birth interval was associated with a significantly higher probabil- ity of being overweight or obese amongst men aged 17-20. Given that a large body of previous research has shown that short and long birth intervals are associated with an increased risk of poor peri-natal outcomes and poor long-term educational and socioeconomic outcomes, there was good reason to believe that this might also translate into worse long-term health. Overall, however, this study suggests that in a high income country such as Sweden, even birth intervals as short as 6-12 months do not have much of a long-term impact on overall health. The pattern that we observe for the probability of being overweight or obese in early adult- hood is intriguing. When the preceding birth interval is 97 months or longer, the index person is, relative to the baseline, 34% more likely to be overweight or obese – a substantial effect size. Previous research has suggested that preterm birth can affect adiposity (Uthaya et al., 2005), which can in turn affect the risk of becoming overweight or obese later in childhood and adult- hood (Mathai et al., 2013). Furthermore, short and long birth intervals have been shown to be related to the risk of preterm birth (Conde-Agudelo et al., 2006). This is a possible explanation for the association that we observe between birth interval length and the probability of being

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• verweight or obese in early adulthood, but if it is the explanation then it surprising that we do

not find that short birth intervals are also associated with an increased risk of becoming over- weight or obese. The true explanation is unclear. One speculative explanation for our findings

• n being overweight is that birth spacing could be related to how the changing family environ-

ment is related to eating habits in childhood, where a child born after a long birth interval is exposed to different food, and consumes more calories. For example, it might be the case that the parents prepare the same dishes and a similar food portion size for all of their children; for a sibling born after a long birth interval this might mean that they are served a portion of food more suitable for a child several years older than them, or food that would generally only be in- troduced to older children, leading to higher calorific consumption through childhood. Indeed, a review of studies indicates that the eating patterns of children are strongly influenced by family and the social environment, and children model the behaviours of those around them (Patrick and Nicklas, 2005). Furthermore, like adults (Wansink et al., 2005), children will generally eat what is put in front of them; larger portions lead to greater consumption (Fisher and Kral, 2008). Ultimately, however, a definitive explanation for our finding remains elusive. Although the sibling comparison approach that we implement in this study has the advantage

• f eliminating confounding from factors shared amongst siblings, it is possible that we fail to

adequately capture the influence of confounding factors that vary amongst siblings. We have attempted to address this issue by adjusting for plausible potential confounding factors such as birth year, maternal age, and birth order, as well as age at conscription test attendance and the year of the conscription test. While residual confounding may remain, we consider this to be a relatively small problem given that we observe almost no statistically significant associations between birth interval length and health and mortality in adulthood. That is, our results are not being driven by omitted variable bias, because we do not observe that birth intervals have much

• f an effect on long-term health. Another limitation of our study is that we do not adjust for the

peri-natal outcomes that we heavily discuss as potential mediating factors for the relationship between birth interval length and the long-term health outcomes that we study. The reason for this is that we do not have access to these variables in the population registers that we have access to. Nevertheless, these peri-natal outcomes are a consequence of the birth interval length and not a confounding factor, so the failure to include these variables in our models does not bias the estimates that we have produced for the effect of birth interval length on health in

• adulthood. Furthermore, again, apart from a higher probability of being overweight we do not
• bserve any negative effect of birth intervals on long-term health, even without adjusting for

these theoretically important mediating factors. A perhaps more important limitation of our study is that the sibling comparison design that we implement is based upon sibling groups with at least three children, as there is no variance

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in birth interval length in a two-child sibling group. It is possible that the effect of birth intervals

• n long-term health is different in two-child sibling groups, the most common family size in

Sweden (Andersson, 1999), than it is in larger sibling groups. However, we think this unlikely. The various theoretical hypotheses that have been proposed to explain a potential relationship between birth interval length and maternal and child health, as well as resource dilution in the household, should all be operating at a more severe level in larger sibling groups than in smaller sibling groups. Larger sibling groups would mean heavier dilution of resources. One would also expect that maternal nutrient depletion, folate depletion, cervical insufficiency, and the transmission of infections would be worse in larger sibling groups. Research on the relationship between birth interval length and child outcomes in the short- and long-term has received a great deal of attention, but the received wisdom on the negative effects of short, and very long, birth intervals (e.g. Powell and Steelman, 1990, 1993; Conde- Agudelo et al., 2006, 2007) has recently been challenged by a series of studies using data from high-income countries that challenge whether birth intervals actually do influence perinatal out- comes (Ball et al., 2014; Hanley et al., 2017), or educational and socioeconomic outcomes (Barclay and Kolk, 2017). This study adds to this literature by showing that in a high-income country, birth interval length does not seem to influence long-term health, with the exception

• f a possible link to becoming overweight or obese. However, as the US Centers for Disease

Control and Prevention has noted (Copen et al., 2015), more research is needed on this topic before a new consensus can be reached. In particular we encourage others with high quality population or state-level data to emulate recent research, including this study, using a within- mother or sibling-comparison design (Ball et al., 2014; Koullali et al., 2016; Shachar et al., 2016; Hanley et al., 2017; Barclay and Kolk, 2017), to evaluate the effect of birth spacing on short- and long-term child outcomes. REFERENCES Adams, M., Delaney, K., Stupp, P., McCarthy, B. and Rawlings, J. (1997), ‘The relationship of interpregnancy interval to infant birthweight and length of gestation among low-risk women, georgia’, Paediatric and Perinatal Epidemiology 11(S1), 48–62. Allison, P. D. (2009), Fixed Effects Regression Models, Vol. 160., SAGE Publications. Andersson, G. (1999), ‘Childbearing trends in sweden, 1961-1997’, European Journal of Pop- ulation 15(1), 1–24. Arafa, M. A., Alkhouly, A. and Youssef, M. E. (2004), ‘Influence of inter-pregnancy interval

• n preterm delivery’, Paediatric and Perinatal Epidemiology 18(4), 248–252.

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Armstrong, N. and Welsman, J. R. (2007), Aerobic fitness: what are we measuring?, in G. R. Tomkinson and T. S. Olds, eds, ‘Pediatric Fitness. Secular Trends and Geographic Variabil- ity.’, Karger, Basel. Bakewell, J., Stockbauer, J. and Schramm, W. (1997), ‘Factors associated with repetition

• f low birthweight: Missouri longitudinal study’, Paediatric and Perinatal Epidemiology

11(S1), 119–129. Ball, S. J., Pereira, G., Jacoby, P., de Klerk, N. and Stanley, F. J. (2014), ‘Re-evaluation of link between interpregnancy interval and adverse birth outcomes: retrospective cohort study matching two intervals per mother’, BMJ 349, g4333. Baranowska-Rataj, A., Barclay, K. and Kolk, M. (2017), ‘The effect of number of siblings on adult mortality: Evidence from swedish registers for cohorts born between 1938 and 1972’, Population Studies 71(1), 43–63. Barclay, K. and Kolk, M. (2015), ‘Birth order and mortality: A population-based cohort study’, Demography 52(2), 613–639. Barclay, K. and Kolk, M. (2017), ‘The long-term cognitive and socioeconomic consequences

• f birth intervals: A within-family sibling comparison using swedish register data’, Demog-

raphy 54(2), 459–484. Barclay, K. and Myrskyl¨ a, M. (2014), ‘Birth order and physical fitness in early adulthood: Evidence from swedish military conscription data’, Social Science & Medicine 123, 141– 148. Barclay, K. and Myrskyl¨ a, M. (2016), ‘Advanced maternal age and offspring outcomes: Re- productive aging and counterbalancing period trends’, Population and Development Review 42(1), 69–94. Barros, F. C., Huttly, S. R., Victora, C. C., Kirkwood, B. R. and Vaughan, J. P. (1992), ‘Com- parison of the causes and consequences of prematurity and intrauterine growth retardation: a longitudinal study in southern brazil’, Pediatrics 90(2), 238–244. Basso, O., Olsen, J., Knudsen, L. B. and Christensen, K. (1998), ‘Low birth weight and preterm birth after short interpregnancy intervals’, American Journal of Obstetrics and Gynecology 178(2), 259–263. Behrman, J. R. and Rosenzweig, M. R. (2004), ‘Returns to birthweight’, Review of Economics and Statistics 86(2), 586–601. Black, S. E., Devereux, P. J. and Salvanes, K. G. (2005), ‘The more the merrier? the effect

• f family size and birth order on children’s education’, Quarterly Journal of Economics

120(2), 669–700. Black, S. E., Devereux, P. J. and Salvanes, K. G. (2007), ‘From the cradle to the labor mar- ket? the effect of birth weight on adult outcomes’, The Quarterly Journal of Economics

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SLIDE 32

SUPPLEMENTARY MATERIALS TABLE S1. Sample Exclusion Process

Preceding Interval 1962-1979 1938-1960 N N excluded N N excluded Total born in Sweden 1,951,202 2,491,059 ID for both parents 1,927,677 23,525 2,210,012 281,047 All siblings born in Sweden 1,893,446 34,231 2,193,609 16,403 No multiple births 1,846,327 47,119 1,980,743 212,866 No half-siblings 1,347,819 498,508 1,735,140 245,603 Sibling group size >2 570,595 777,224 871,081 864,059 Males only 294,808 275,787

• Outmigration or death before 1990
• 836,583

34,498 No first-borns 209,361 85,447 596,833 239,750 Cohort cut 125,340 84,021 581,544 15,289 Within-group variance in mortality

• 159,554

421,990 No missing values on model variables

∼105,000

20,340 159,554 Final

∼105,000

159,554 Subsequent Interval 1962-1979 1938-1960 N N excluded N N excluded Total born in Sweden 1,951,202 2,491,059 ID for both parents 1,927,677 23,525 2,210,012 281,047 All siblings born in Sweden 1,893,446 34,231 2,193,609 16,403 No multiple births 1,846,327 47,119 1,980,743 212,866 No half-siblings 1,347,819 498,508 1,735,140 245,603 Sibling group size >2 570,595 777,224 871,081 864,059 Males only 294,808 275,787

• Outmigration or death before 1990
• 836,583

34,498 No last-borns 198,431 96,377 639,628 196,955 Cohort cut 132,618 65,813 606,515 33,113 Within-group variance in mortality

• 150,907

455,608 No missing values on model variables

∼110,000

22,618 150,907 Final

∼110,000

150,907

Note: Final sample for 1962-1979 cohorts varies slightly by outcome variable.

SLIDE 33

TABLE S2. Descriptive Statistics: Length of the Preceding Birth Interval in Relation to Physical Fitness, Height, and Being Underweight or Severely Underweight at Ages 17-20.

Preceding Birth Interval 6-12 13-18 19-24 25-30 31-36 37-42 43-48 49-54 55-60 61-66 67-72 73-78 79-84 85-90 91-96 >96 Everyone Physical N 1,148 8,522 13,550 14,266 13,648 10,784 8,575 6,733 5,461 4,016 3,142 2,521 2,061 1,520 1,135 3,565 100,647 Fitness (watts) Mean fitness 295.1 297.0 299.6 301.4 300.9 299.9 299.0 299.1 298.3 298.6 298.9 299.1 298.1 297.8 299.4 297.5 299.4 Birth order Mean 2.6 2.7 2.6 2.5 2.6 2.7 2.8 2.9 3.0 3.1 3.1 3.1 3.2 3.2 3.2 3.2 2.8 Maternal age Mean 24.9 26.3 26.7 27.0 27.5 28.1 28.8 29.6 30.3 30.8 31.3 31.7 32.3 32.8 33.3 34.8 28.5 Birth year Mean 1969.6 1969.9 1970.4 1970.8 1970.9 1970.9 1970.9 1971.0 1971.0 1971.2 1971.4 1971.7 1971.9 1972.3 1972.5 1973.1 1970.9 Sibling group size Mean 3.8 3.8 3.6 3.5 3.4 3.4 3.5 3.5 3.5 3.5 3.5 3.4 3.5 3.5 3.4 3.5 3.5 Fitness by birth year 1962-1964 245.9 258.2 262.2 258.5 267.9 262.4 263.8 256.2 256.7 276.3 310.7 242.5 198.0 287.5 252.0 261.2 261.3 1965-1969 290.5 291.1 293.1 294.6 295.0 293.4 293.3 292.3 291.8 293.1 294.5 293.1 298.3 295.4 295.0 288.3 293.3 1970-1974 303.7 303.4 305.4 307.3 304.3 304.9 301.8 303.1 302.9 301.5 299.8 301.1 297.7 297.7 299.7 300.6 303.5 1975-1979 294.3 304.8 306.6 306.3 307.0 304.4 305.4 304.6 301.9 301.5 303.7 302.7 298.8 300.2 302.5 297.0 304.4 Height (cm) N 1,184 8,906 14,266 15,156 14,538 11,540 9,191 7,228 5,875 4,321 3,416 2,730 2,227 1,659 1,246 4,027 107,510 Mean height 178.8 179.3 179.5 179.5 179.5 179.5 179.5 179.6 179.5 179.5 179.7 179.6 179.4 179.6 179.9 179.5 179.5 Birth order Mean 2.6 2.7 2.6 2.5 2.6 2.7 2.8 2.9 3.0 3.1 3.1 3.1 3.2 3.2 3.2 3.2 2.8 Maternal age Mean 24.9 26.3 26.7 27.0 27.5 28.1 28.8 29.6 30.3 30.8 31.3 31.8 32.3 32.8 33.3 34.8 28.5 Birth year Mean 1969.8 1970.2 1970.7 1971.1 1971.3 1971.3 1971.3 1971.4 1971.4 1971.6 1971.9 1972.1 1972.3 1972.7 1972.9 1973.5 1971.3 Sibling group size Mean 3.8 3.8 3.6 3.5 3.4 3.4 3.5 3.5 3.5 3.5 3.5 3.4 3.5 3.5 3.5 3.5 3.5 Fitness by birth year 1962-1964 176.7 178.1 179.3 178.6 180.5 178.2 180.8 179.5 179.3 180.6 181.7 177.0 175.0 179.0 179.0 180.2 179.1 1965-1969 178.4 179.0 179.2 179.2 179.3 179.1 179.3 179.4 179.1 179.2 179.7 179.3 178.9 179.4 179.3 179.0 179.2 1970-1974 179.5 179.6 179.8 179.6 179.5 179.7 179.4 179.6 179.8 179.5 179.5 179.7 179.4 179.6 180.0 179.5 179.6 1975-1979 178.8 179.6 179.7 179.9 179.7 179.8 179.6 179.8 179.4 179.8 180.1 179.8 179.8 179.6 180.2 179.6 179.7 Underweight N 1,132 8,530 13,643 14,422 13,813 10,957 8,698 6,852 5,571 4,086 3,197 2,555 2,091 1,561 1,143 3,749 102,000

• r Severely

% 6.4 7.5 6.5 6.8 6.9 7.1 6.4 7.3 6.7 5.9 7.3 7.9 6.7 6.1 4.5 6.0 6.8 Underweight Birth order Mean 2.7 2.6 2.6 2.5 2.6 2.7 2.8 2.9 3.0 3.1 3.1 3.1 3.2 3.2 3.2 3.2 2.7 Maternal age Mean 25.0 26.3 26.7 27.0 27.5 28.2 28.8 29.6 30.3 30.8 31.3 31.7 32.4 32.8 33.3 34.8 28.6 Birth year Mean 1969.7 1970.1 1970.6 1971.0 1971.2 1971.2 1971.2 1971.3 1971.3 1971.5 1971.8 1971.9 1972.2 1972.6 1972.8 1973.4 1971.2 Sibling group size Mean 3.8 3.8 3.6 3.5 3.4 3.4 3.5 3.5 3.5 3.5 3.5 3.4 3.5 3.5 3.5 3.5 3.5 % by birth year 1962-1964 0.0 5.3 6.3 8.5 3.7 9.0 7.5 7.1 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 6.2 1965-1969 6.4 7.9 6.9 7.4 7.6 8.0 6.7 8.0 7.1 6.6 8.1 10.1 8.3 4.3 4.3 5.3 7.4 1970-1974 6.6 7.9 6.8 6.7 7.1 7.2 7.0 7.3 7.0 5.9 7.5 7.4 6.8 7.3 5.9 6.5 7.0 1975-1979 6.1 5.9 5.3 5.9 5.8 5.6 5.1 6.2 5.7 4.9 6.2 6.3 5.0 5.6 2.9 5.7 5.6

SLIDE 34

TABLE S3. Descriptive Statistics: Length of the Preceding Birth Interval in Relation to Being Overweight or Obese at Ages 17-20, and Mortality at Ages 30-74.

Preceding Birth Interval 6-12 13-18 19-24 25-30 31-36 37-42 43-48 49-54 55-60 61-66 67-72 73-78 79-84 85-90 91-96 >96 Everyone Overweight N 1,132 8,530 13,643 14,422 13,813 10,957 8,698 6,852 5,571 4,086 3,197 2,555 2,091 1,561 1,143 3,749 102,000

• r Obese

% 9.5 10.2 9.9 9.8 11.0 11.0 11.3 11.5 13.0 13.2 13.9 14.1 15.3 15.4 17.1 18.0 11.5 Birth order Mean 2.7 2.6 2.6 2.5 2.6 2.7 2.8 2.9 3.0 3.1 3.1 3.1 3.2 3.2 3.2 3.2 2.7 Maternal age Mean 25.0 26.3 26.7 27.0 27.5 28.2 28.8 29.6 30.3 30.8 31.3 31.7 32.4 32.8 33.3 34.8 28.6 Birth year Mean 1969.7 1970.1 1970.6 1971.0 1971.2 1971.2 1971.2 1971.3 1971.3 1971.5 1971.8 1971.9 1972.2 1972.6 1972.8 1973.4 1971.2 Sibling group size Mean 3.8 3.8 3.6 3.5 3.4 3.4 3.5 3.5 3.5 3.5 3.5 3.4 3.5 3.5 3.5 3.5 3.5 % by birth year 1962-1964 7.7 9.6 7.7 7.7 13.6 4.5 5.7 2.4 10.0 0.0 0.0 0.0 0.0 25.0 0.0 33.3 8.0 1965-1969 8.1 9.7 8.8 8.5 9.9 9.8 10.0 9.8 12.5 11.5 12.0 10.8 13.3 15.4 16.9 16.6 10.0 1970-1974 11.2 9.3 9.7 10.0 10.8 10.9 11.1 11.8 12.0 13.5 14.5 13.7 14.8 13.7 17.1 17.3 11.5 1975-1979 10.2 13.1 12.7 11.7 12.6 13.1 13.8 13.5 15.0 14.9 15.1 17.9 18.0 17.9 17.2 19.1 13.9 Mortality Mortality rate (10−3) 1.22 1.20 1.18 1.25 1.23 1.24 1.21 1.22 1.12 1.16 1.16 1.09 1.06 1.00 0.95 0.84 1.18 Deaths 659 6,322 7,366 6,230 5,038 3,982 3,269 2,586 2,041 1,659 1,349 1,026 822 596 477 1,635 45,057 Person-time % 1.4 13.8 16.2 13.0 10.7 8.4 7.0 5.5 4.8 3.7 3.0 2.5 2.0 1.6 1.3 5.1 100.0 Sex % 47.0 46.5 48.0 46.1 46.8 46.5 46.6 46.9 47.1 46.2 46.9 48.2 46.5 48.1 46.3 47.2 46.9 Birth order Mean 3.1 3.3 3.3 3.3 3.2 3.2 3.2 3.2 3.2 3.2 3.2 3.3 3.3 3.3 3.3 3.3 3.2 Maternal age Mean 26.8 28.0 29.2 29.9 30.3 30.8 31.3 31.7 32.3 32.9 33.1 33.7 34.2 34.6 35.1 36.8 30.8 Birth year Mean 1947.0 1946.6 1946.8 1947.2 1947.7 1948.0 1948.4 1948.7 1949.2 1949.4 1949.7 1950.2 1950.7 1951.2 1951.6 1953.5 1948.2 Sibling group size Mean 5.0 4.9 4.8 4.6 4.4 4.3 4.2 4.1 4.1 4.0 3.9 3.9 3.9 3.8 3.8 3.6 4.4 Rate by birth year 1938-1940 1.50 1.73 1.93 2.16 2.31 2.46 2.48 2.58 2.63 2.85 2.66 2.70 3.04 2.98 2.59 2.76 2.12 1941-1945 1.45 1.31 1.30 1.41 1.42 1.48 1.52 1.73 1.59 1.85 1.87 2.01 2.16 2.01 2.39 2.58 1.47 1946-1950 1.09 1.04 1.00 1.06 1.06 1.09 1.06 1.03 0.96 1.08 1.09 1.04 1.07 1.17 1.06 1.29 1.05 1951-1955 0.97 0.87 0.88 0.94 0.91 0.89 0.89 0.84 0.84 0.78 0.83 0.81 0.73 0.75 0.68 0.65 0.85 1956-1960 0.97 1.00 0.88 0.91 0.88 0.89 0.86 0.83 0.70 0.56 0.65 0.53 0.62 0.49 0.61 0.54 0.77

SLIDE 35

TABLE S4. Descriptive Statistics: Length of the Subsequent Birth Interval in Relation to Physical Fitness, Height, and Being Underweight or Severely Underweight at Ages 17-20.

Subsequent Birth Interval 6-12 13-18 19-24 25-30 31-36 37-42 43-48 49-54 55-60 61-66 67-72 73-78 79-84 85-90 91-96 >96 Everyone Physical Fitness N 1,017 7,658 12,646 13,724 13,474 10,691 8,793 6,950 5,771 4,607 3,600 3,013 2,585 2,119 1,718 7,576 105,942 Mean fitness 294.4 298.5 301.7 302.2 302.3 301.5 302.4 301.4 299.8 301.5 300.8 302.3 301.5 299.5 299.4 299.7 301.2 Birth order Mean 1.6 1.6 1.5 1.5 1.5 1.6 1.7 1.8 1.9 2.0 2.1 2.1 2.1 2.1 2.2 2.2 1.7 Maternal age Mean 23.9 25.1 24.9 24.8 24.7 24.9 25.1 25.2 25.4 25.6 25.5 25.6 25.5 25.6 25.6 25.2 25.1 Birth year Mean 1969.4 1970.0 1970.6 1970.9 1971.0 1971.0 1971.1 1971.0 1971.0 1971.2 1971.0 1971.1 1971.2 1971.2 1971.5 1971.4 1970.9 Sibling group size Mean 3.8 3.7 3.6 3.5 3.4 3.4 3.4 3.4 3.4 3.4 3.4 3.4 3.4 3.4 3.4 3.4 3.5 Fitness by birth year 1962-1964 250.6 261.1 260.5 269.3 274.5 272.8 258.6 262.1 265.1 258.1 256.2 267.4 239.1 240.5 270.0 256.6 264.0 1965-1969 290.4 291.2 294.7 295.6 296.7 293.7 297.3 294.8 294.1 295.6 294.7 296.3 294.3 295.3 292.6 291.7 294.7 1970-1974 302.2 307.0 307.5 308.1 306.6 307.8 306.7 306.4 304.6 306.3 305.6 307.0 305.2 301.5 303.6 304.3 306.5 1975-1979 291.0 305.5 307.6 305.3 305.6 305.8 305.4 305.8 303.2 304.8 304.9 305.8 308.9 304.0 301.8 303.8 305.4 Height (cm) N 1,043 8,025 13,464 14,639 14,422 11,457 9,423 7,450 6,182 4,966 3,869 3,246 2,787 2,260 1,861 8,156 113,250 Mean height 178.6 179.4 179.8 179.6 179.6 179.5 179.6 179.5 179.5 179.4 179.4 179.4 179.3 179.5 179.1 179.3 179.5 Birth order Mean 1.6 1.6 1.5 1.5 1.5 1.6 1.7 1.8 1.9 2.0 2.0 2.1 2.1 2.1 2.2 2.2 1.7 Maternal age Mean 23.9 25.1 25.0 24.8 24.7 24.9 25.1 25.3 25.5 25.6 25.6 25.6 25.6 25.6 25.6 25.2 25.1 Birth year Mean 1969.6 1970.3 1971.0 1971.3 1971.4 1971.4 1971.5 1971.4 1971.4 1971.6 1971.5 1971.5 1971.6 1971.6 1972.0 1971.8 1971.3 Sibling group size Mean 3.8 3.7 3.6 3.5 3.4 3.4 3.4 3.4 3.4 3.4 3.4 3.4 3.4 3.4 3.4 3.4 3.5 Fitness by birth year 1962-1964 177.9 178.3 179.7 179.3 180.1 179.2 179.1 179.0 181.0 180.1 179.3 181.5 179.1 178.0 182.5 179.1 179.4 1965-1969 178.3 179.2 179.4 179.4 179.3 179.1 179.3 179.2 179.4 179.1 179.2 179.1 178.9 179.3 179.1 178.9 179.2 1970-1974 178.9 179.8 179.8 179.8 179.8 179.7 179.7 179.6 179.4 179.5 179.7 179.6 179.5 179.9 179.2 179.5 179.7 1975-1979 179.1 179.4 180.1 179.8 179.8 179.8 179.7 179.7 179.8 179.6 179.5 179.4 179.3 179.5 179.1 179.3 179.7 Underweight N 997 7,688 12,885 14,012 13,782 10,973 8,965 7,082 5,907 4,727 3,653 3,070 2,648 2,142 1,772 7,721 108,024

• r Severely

% 6.8 7.2 7.3 7.1 7.1 7.3 7.3 7.0 7.0 6.8 6.7 6.1 6.6 7.4 6.5 6.3 7.0 Underweight Birth order Mean 1.6 1.6 1.5 1.5 1.5 1.6 1.7 1.8 1.9 2.0 2.1 2.1 2.1 2.1 2.2 2.2 1.7 Maternal age Mean 24.0 25.1 25.0 24.8 24.8 24.9 25.1 25.3 25.5 25.6 25.6 25.6 25.6 25.6 25.7 25.2 25.1 Birth year Mean 1969.5 1970.2 1970.9 1971.2 1971.3 1971.3 1971.4 1971.3 1971.3 1971.5 1971.3 1971.4 1971.5 1971.5 1971.9 1971.7 1971.2 Sibling group size Mean 3.8 3.7 3.6 3.5 3.4 3.4 3.4 3.4 3.4 3.4 3.4 3.4 3.4 3.4 3.4 3.4 3.5 % by birth year 1962-1964 12.5 11.7 10.6 2.7 5.5 7.7 10.0 0.0 8.9 8.0 12.5 12.5 11.1 20.0 0.0 7.0 7.7 1965-1969 6.1 8.5 7.9 7.4 7.2 8.0 7.4 8.3 7.0 7.9 7.2 6.4 6.6 7.0 6.6 7.2 7.5 1970-1974 7.9 6.7 7.4 7.2 7.5 7.5 7.2 7.5 8.4 6.4 7.1 6.6 7.5 9.4 5.7 6.5 7.3 1975-1979 6.4 4.6 6.3 6.6 6.4 6.2 7.1 5.1 5.4 5.9 5.4 5.1 5.8 5.2 7.4 5.0 6.0

SLIDE 36

TABLE S5. Descriptive Statistics: Length of the Subsequent Birth Interval in Relation to Being Overweight or Obese at Ages 17-20, and Mortality at Ages 30-74.

Subsequent Birth Interval 6-12 13-18 19-24 25-30 31-36 37-42 43-48 49-54 55-60 61-66 67-72 73-78 79-84 85-90 91-96 >96 Everyone Overweight N 997 7,688 12,885 14,012 13,782 10,973 8,965 7,082 5,907 4,727 3,653 3,070 2,648 2,142 1,772 7,721 108,024

• r Obese

% 11.7 10.9 10.3 10.8 10.5 10.9 10.8 11.2 10.7 10.8 10.3 11.4 10.4 11.3 10.8 11.1 10.8 Birth order Mean 1.6 1.6 1.5 1.5 1.5 1.6 1.7 1.8 1.9 2.0 2.1 2.1 2.1 2.1 2.2 2.2 1.7 Maternal age Mean 24.0 25.1 25.0 24.8 24.8 24.9 25.1 25.3 25.5 25.6 25.6 25.6 25.6 25.6 25.7 25.2 25.1 Birth year Mean 1969.5 1970.2 1970.9 1971.2 1971.3 1971.3 1971.4 1971.3 1971.3 1971.5 1971.3 1971.4 1971.5 1971.5 1971.9 1971.7 1971.2 Sibling group size Mean 3.8 3.7 3.6 3.5 3.4 3.4 3.4 3.4 3.4 3.4 3.4 3.4 3.4 3.4 3.4 3.4 3.5 % by birth year 1962-1964 0.0 5.8 6.2 10.9 7.3 7.7 8.0 14.3 13.3 8.0 0.0 18.8 0.0 0.0 20.0 11.6 8.4 1965-1969 10.9 9.6 9.3 9.6 9.6 9.7 9.8 9.4 8.8 9.1 8.9 9.9 9.1 9.6 9.6 9.9 9.5 1970-1974 12.9 11.1 9.8 10.9 10.0 10.3 9.9 11.7 9.9 10.8 10.0 10.0 9.6 11.3 10.3 10.4 10.4 1975-1979 12.8 14.2 12.8 12.6 12.6 13.3 13.2 13.0 14.1 13.0 13.0 14.8 13.0 13.7 12.3 13.4 13.1 Mortality Mortality rate (10−3) 1.25 1.32 1.37 1.41 1.46 1.49 1.56 1.52 1.60 1.61 1.59 1.58 1.64 1.66 1.63 1.68 1.47 Deaths 624 6,352 7,658 6,287 5,374 4,337 3,758 2,943 2,606 2,125 1,689 1,398 1,215 980 843 3,820 52,009 Person-time % 1.4 13.6 15.9 12.6 10.4 8.2 6.8 5.5 4.6 3.7 3.0 2.5 2.1 1.7 1.5 6.4 100.0 Sex % 49.5 47.3 46.5 46.7 47.2 46.3 45.9 45.3 43.4 45.6 44.4 46.5 45.4 45.2 46.4 45.8 46.3 Birth order Mean 2.0 2.2 2.3 2.3 2.2 2.2 2.2 2.3 2.3 2.4 2.4 2.5 2.5 2.5 2.5 2.5 2.285 Maternal age Mean 25.6 26.5 27.2 27.5 27.4 27.6 27.6 27.6 27.7 27.9 27.7 27.8 27.7 27.7 27.7 27.1 27.338 Birth year Mean 1946.5 1945.8 1945.7 1945.8 1946.0 1946.0 1946.1 1946.3 1946.4 1946.4 1946.6 1946.7 1946.9 1946.9 1947.0 1947.1 1946.121 Sibling group size Mean 4.9 4.8 4.7 4.5 4.4 4.2 4.1 4.1 4.0 4.0 3.9 3.9 3.9 3.8 3.8 3.7 4.346 Rate by birth year 1938-1940 1.65 1.73 1.79 1.89 1.98 2.02 2.27 2.31 2.51 2.48 2.57 2.50 2.68 2.87 2.65 3.07 2.08 1941-1945 1.31 1.39 1.44 1.51 1.55 1.60 1.61 1.60 1.73 1.78 1.79 1.73 1.84 1.87 1.95 1.94 1.57 1946-1950 1.32 1.11 1.20 1.17 1.30 1.28 1.31 1.27 1.30 1.33 1.26 1.30 1.37 1.20 1.17 1.28 1.24 1951-1955 0.87 1.10 1.07 1.12 1.12 1.16 1.19 1.11 1.22 1.13 1.09 1.20 1.16 1.22 1.23 1.31 1.14 1956-1960 0.85 1.07 1.07 1.07 1.14 1.13 1.28 1.18 1.14 1.10 1.17 1.14 1.19 1.43 1.24 1.28 1.14

SLIDE 37

TABLE S6. Results: Relationship Between Preceding Birth Interval and Physi- cal Fitness for Swedish Men Born 1962-1979. Estimates for Age at Conscription Test and Year of Conscription Test Not Shown.

Within-family Between-family Beta SE 95% CI Beta SE 95% CI Preceding 6-12

• 0.013

0.047

• 0.105, 0.079
• 0.010

0.029

• 0.067, 0.047

Interval Length 13-18

• 0.054

0.022

• 0.096, -0.011
• 0.015

0.013

• 0.041, 0.011

19-24

• 0.054

0.019

• 0.092, -0.016
• 0.003

0.012

• 0.026, 0.020

25-30 (ref) 0.000 0.000 31-36

• 0.061

0.020

• 0.100, -0.022
• 0.034

0.012

• 0.057, -0.011

37-42

• 0.048

0.021

• 0.090, -0.006
• 0.058

0.012

• 0.082, -0.034

43-48

• 0.061

0.023

• 0.106, -0.016
• 0.078

0.013

• 0.104, -0.052

49-54

• 0.053

0.025

• 0.103, -0.004
• 0.083

0.015

• 0.112, -0.055

55-60

• 0.041

0.028

• 0.095, 0.013
• 0.102

0.015

• 0.132, -0.071

61-66

• 0.112

0.031

• 0.174, -0.051
• 0.109

0.017

• 0.143, -0.075

67-72

• 0.067

0.036

• 0.137, 0.004
• 0.126

0.020

• 0.165, -0.087

73-78

• 0.075

0.039

• 0.152, 0.002
• 0.140

0.021

• 0.182, -0.099

79-84

• 0.073

0.044

• 0.160, 0.014
• 0.168

0.024

• 0.214, -0.121

85-90

• 0.070

0.050

• 0.168, 0.028
• 0.177

0.026

• 0.228, -0.126

91-96 0.011 0.058

• 0.102, 0.125
• 0.154

0.030

• 0.213, -0.095

97+

• 0.040

0.044

• 0.126, 0.045
• 0.190

0.020

• 0.228, -0.151

Birth Order 2 (ref) 0.000 0.000 3

• 0.066

0.020

• 0.105, -0.026
• 0.116

0.007

• 0.131, -0.102

4

• 0.056

0.039

• 0.133, 0.021
• 0.189

0.014

• 0.215, -0.162

5

• 0.136

0.060

• 0.254, -0.018
• 0.264

0.025

• 0.312, -0.215

6

• 0.189

0.083

• 0.352, -0.026
• 0.310

0.037

• 0.383, -0.236

7+

• 0.129

0.109

• 0.342, 0.084
• 0.291

0.048

• 0.385, -0.198

Maternal Age 15-19

• 0.099

0.065

• 0.227, 0.028
• 0.336

0.033

• 0.402, -0.271

20-24 0.006 0.021

• 0.035, 0.048
• 0.157

0.009

• 0.174, -0.140

25-29 (ref) 0.000 0.000 30-34 0.002 0.021

• 0.038, 0.043

0.102 0.008 0.085, 0.118 35-39

• 0.029

0.040

• 0.106, 0.049

0.122 0.013 0.097, 0.147 40-44

• 0.091

0.070

• 0.228, 0.047

0.098 0.026 0.047, 0.150 45+ 0.042 0.194

• 0.337, 0.421

0.057 0.109

• 0.156, 0.270

Birth Year 1962

• 0.924

0.764

• 2.421, 0.574
• 0.338

0.208

• 0.747, 0.070

1963

• 1.197

0.250

• 1.686, -0.707
• 0.804

0.134

• 1.067, -0.542

1964

• 0.771

0.166

• 1.097, -0.445
• 0.472

0.093

• 0.655, -0.290

1965

• 0.576

0.144

• 0.860, -0.293
• 0.354

0.083

• 0.517, -0.191

1966

• 0.330

0.119

• 0.563, -0.096
• 0.205

0.071

• 0.344, -0.065

1967

• 0.253

0.100

• 0.448, -0.057
• 0.170

0.060

• 0.288, -0.053

1968

• 0.310

0.076

• 0.458, -0.161
• 0.253

0.046

• 0.343, -0.163

1969

• 0.091

0.054

• 0.197, 0.014
• 0.133

0.034

• 0.200, -0.067

1970 (ref) 0.000 0.000 1971

• 0.072

0.049

• 0.168, 0.023
• 0.095

0.032

• 0.158, -0.032

1972 0.014 0.068

• 0.119, 0.147
• 0.036

0.044

• 0.123, 0.051

1973

• 0.017

0.085

• 0.183, 0.149
• 0.026

0.054

• 0.133, 0.080

1974 0.006 0.101

• 0.191, 0.204
• 0.014

0.063

• 0.138, 0.109

1975 0.199 0.116

• 0.028, 0.426

0.196 0.071 0.056, 0.336 1976 0.344 0.133 0.084, 0.604 0.388 0.080 0.231, 0.545 1977 0.527 0.156 0.222, 0.832 0.570 0.090 0.393, 0.746 1978 0.683 0.181 0.328, 1.038 0.770 0.102 0.570, 0.970 1979 0.841 0.225 0.400, 1.283 0.813 0.120 0.578, 1.048 Sibling 3 (ref) 0.000 Group Size 4

• 0.038

0.009

• 0.056, -0.020

5

• 0.100

0.017

• 0.133, -0.068

6

• 0.105

0.027

• 0.157, -0.053

7

• 0.154

0.034

• 0.221, -0.087

N 100,647 100,647

SLIDE 38

TABLE S7. Results: Relationship Between Subsequent Birth Interval and Phys- ical Fitness for Swedish Men Born 1962-1979. Estimates for Age at Conscrip- tion Test and Year of Conscription Test Not Shown.

Within-family Between-family Beta SE 95% CI Beta SE 95% CI Subsequent 6-12 0.016 0.046

• 0.074, 0.107
• 0.072

0.032

• 0.135, -0.008

Interval Length 13-18 0.016 0.022

• 0.027, 0.058
• 0.020

0.014

• 0.047, 0.007

19-24 0.014 0.018

• 0.022, 0.050

0.007 0.012

• 0.016, 0.030

25-30 (ref) 0.000 0.000 31-36 0.001 0.018

• 0.035, 0.037
• 0.005

0.012

• 0.028, 0.018

37-42 0.009 0.020

• 0.029, 0.048
• 0.016

0.012

• 0.040, 0.008

43-48 0.008 0.022

• 0.034, 0.051
• 0.003

0.013

• 0.029, 0.023

49-54 0.004 0.024

• 0.042, 0.051
• 0.009

0.014

• 0.037, 0.019

55-60

• 0.008

0.025

• 0.058, 0.042
• 0.031

0.015

• 0.061, -0.001

61-66 0.037 0.027

• 0.017, 0.091
• 0.007

0.017

• 0.040, 0.026

67-72 0.018 0.031

• 0.042, 0.078
• 0.014

0.018

• 0.050, 0.022

73-78 0.011 0.033

• 0.052, 0.075

0.007 0.020

• 0.031, 0.046

79-84 0.036 0.035

• 0.033, 0.105

0.006 0.021

• 0.035, 0.048

85-90 0.011 0.038

• 0.065, 0.086
• 0.037

0.023

• 0.082, 0.008

91-96 0.021 0.041

• 0.059, 0.100
• 0.043

0.024

• 0.091, 0.004

97+

• 0.001

0.024

• 0.048, 0.046
• 0.033

0.014

• 0.061, -0.005

Birth Order 1 0.000 0.021

• 0.041, 0.041

0.069 0.007 0.055, 0.082 2 (ref) 0.000 0.000 3

• 0.024

0.024

• 0.072, 0.024
• 0.083

0.012

• 0.107, -0.059

4 0.021 0.048

• 0.074, 0.116
• 0.161

0.024

• 0.208, -0.113

5

• 0.072

0.078

• 0.225, 0.081
• 0.214

0.043

• 0.298, -0.130

6

• 0.074

0.113

• 0.297, 0.148
• 0.235

0.059

• 0.351, -0.119

Maternal Age 15-19

• 0.006

0.033

• 0.070, 0.059
• 0.256

0.013

• 0.282, -0.230

20-24 0.009 0.017

• 0.024, 0.042
• 0.139

0.007

• 0.153, -0.125

25-29 (ref) 0.000 0.000 30-34

• 0.002

0.022

• 0.046, 0.041

0.034 0.010 0.014, 0.055 35-39 0.051 0.059

• 0.065, 0.166

0.001 0.024

• 0.045, 0.048

40-44 0.291 0.197

• 0.096, 0.678
• 0.054

0.083

• 0.217, 0.109

45+

• 0.075

0.032

• 0.139, -0.012

Birth Year 1962

• 0.272

0.824

• 1.886, 1.343
• 0.040

0.232

• 0.494, 0.415

1963

• 1.312

0.260

• 1.822, -0.801
• 0.894

0.123

• 1.136, -0.652

1964

• 0.677

0.157

• 0.984, -0.370
• 0.477

0.088

• 0.650, -0.303

1965

• 0.727

0.133

• 0.987, -0.466
• 0.388

0.079

• 0.543, -0.233

1966

• 0.432

0.108

• 0.644, -0.221
• 0.228

0.068

• 0.362, -0.094

1967

• 0.337

0.086

• 0.506, -0.169
• 0.186

0.057

• 0.298, -0.074

1968

• 0.436

0.066

• 0.566, -0.306
• 0.292

0.046

• 0.381, -0.203

1969

• 0.190

0.047

• 0.282, -0.098
• 0.140

0.034

• 0.206, -0.074

1970 (ref) 0.000 0.000 1971

• 0.056

0.044

• 0.142, 0.030
• 0.108

0.031

• 0.169, -0.047

1972 0.093 0.061

• 0.027, 0.212
• 0.011

0.043

• 0.095, 0.073

1973 0.068 0.075

• 0.080, 0.215
• 0.007

0.052

• 0.108, 0.094

1974 0.106 0.090

• 0.070, 0.283

0.015 0.061

• 0.103, 0.134

1975 0.345 0.104 0.142, 0.548 0.189 0.069 0.055, 0.324 1976 0.489 0.118 0.257, 0.721 0.418 0.076 0.269, 0.567 1977 0.639 0.137 0.370, 0.908 0.623 0.085 0.456, 0.790 1978 0.885 0.159 0.573, 1.198 0.862 0.096 0.673, 1.051 1979 1.015 0.200 0.622, 1.407 0.914 0.113 0.693, 1.135 Sibling 3 (ref) 0.000 Group Size 4

• 0.056

0.009

• 0.074, -0.038

5

• 0.132

0.017

• 0.165, -0.100

6

• 0.133

0.028

• 0.188, -0.079

7

• 0.171

0.035

• 0.241, -0.102

N 105,942 105,942

SLIDE 39

TABLE S8. Results: Relationship Between Preceding Birth Interval and Height for Swedish Men Born 1962-1979. Estimates for Age at Conscription Test and Year of Conscription Test Not Shown.

Within-family Between-family Beta SE 95% CI Beta SE 95% CI Preceding 6-12

• 0.033

0.038

• 0.107, 0.042
• 0.030

0.030

• 0.088, 0.028

Interval Length 13-18

• 0.011

0.017

• 0.045, 0.024

0.006 0.013

• 0.020, 0.031

19-24

• 0.004

0.016

• 0.034, 0.027

0.015 0.011

• 0.007, 0.037

25-30 (ref) 0.000 0.000 31-36

• 0.015

0.016

• 0.047, 0.016
• 0.016

0.011

• 0.038, 0.006

37-42

• 0.018

0.017

• 0.052, 0.016
• 0.029

0.012

• 0.052, -0.005

43-48

• 0.012

0.018

• 0.048, 0.024
• 0.035

0.013

• 0.060, -0.010

49-54 0.020 0.020

• 0.020, 0.059
• 0.027

0.014

• 0.054, 0.001

55-60 0.013 0.022

• 0.030, 0.057
• 0.051

0.015

• 0.080, -0.021

61-66 0.016 0.025

• 0.033, 0.065
• 0.055

0.017

• 0.088, -0.022

67-72 0.011 0.028

• 0.044, 0.067
• 0.024

0.019

• 0.061, 0.014

73-78

• 0.009

0.031

• 0.069, 0.052
• 0.057

0.021

• 0.097, -0.016

79-84

• 0.008

0.035

• 0.077, 0.061
• 0.092

0.023

• 0.137, -0.047

85-90

• 0.011

0.039

• 0.088, 0.066
• 0.070

0.025

• 0.118, -0.022

91-96 0.075 0.045

• 0.013, 0.163
• 0.026

0.029

• 0.082, 0.031

97+ 0.011 0.034

• 0.056, 0.077
• 0.112

0.018

• 0.148, -0.076

Birth Order 2 (ref) 0.000 0.000 3

• 0.048

0.016

• 0.079, -0.017
• 0.070

0.007

• 0.083, -0.057

4

• 0.074

0.031

• 0.135, -0.013
• 0.140

0.013

• 0.166, -0.115

5

• 0.108

0.048

• 0.202, -0.014
• 0.184

0.023

• 0.229, -0.138

6

• 0.098

0.066

• 0.228, 0.032
• 0.225

0.036

• 0.295, -0.155

7 0.031 0.087

• 0.139, 0.202
• 0.286

0.052

• 0.388, -0.185

Maternal Age 15-19

• 0.025

0.053

• 0.128, 0.079
• 0.340

0.034

• 0.408, -0.273

20-24 0.013 0.017

• 0.021, 0.046
• 0.142

0.008

• 0.158, -0.125

25-29 (ref) 0.000 0.000 30-34

• 0.009

0.017

• 0.041, 0.024

0.110 0.008 0.095, 0.126 35-39

• 0.028

0.032

• 0.090, 0.034

0.156 0.013 0.131, 0.181 40-44

• 0.064

0.056

• 0.173, 0.046

0.154 0.025 0.105, 0.203 45+

• 0.064

0.152

• 0.363, 0.234

0.182 0.092 0.002, 0.362 Birth Year 1962 0.213 0.640

• 1.041, 1.467

0.654 0.352

• 0.037, 1.344

1963

• 0.064

0.208

• 0.471, 0.344

0.298 0.152 0.001, 0.596 1964

• 0.014

0.136

• 0.281, 0.253

0.447 0.094 0.263, 0.631 1965 0.072 0.118

• 0.159, 0.304

0.423 0.082 0.262, 0.584 1966 0.025 0.098

• 0.167, 0.217

0.318 0.069 0.182, 0.453 1967 0.016 0.082

• 0.144, 0.176

0.275 0.059 0.160, 0.389 1968

• 0.016

0.062

• 0.138, 0.106

0.225 0.045 0.136, 0.314 1969

• 0.020

0.044

• 0.107, 0.067

0.108 0.034 0.041, 0.174 1970 (ref) 0.000 0.000 1971 0.022 0.040

• 0.056, 0.100

0.010 0.031

• 0.052, 0.071

1972

• 0.021

0.055

• 0.129, 0.087
• 0.118

0.042

• 0.202, -0.035

1973

• 0.074

0.068

• 0.208, 0.060
• 0.204

0.052

• 0.306, -0.102

1974

• 0.096

0.081

• 0.255, 0.063
• 0.273

0.060

• 0.391, -0.155

1975

• 0.116

0.093

• 0.298, 0.066
• 0.338

0.068

• 0.471, -0.204

1976

• 0.081

0.106

• 0.288, 0.127
• 0.330

0.076

• 0.479, -0.181

1977

• 0.047

0.122

• 0.285, 0.192
• 0.367

0.085

• 0.533, -0.200

1978 0.085 0.137

• 0.183, 0.353
• 0.275

0.093

• 0.457, -0.093

1979 0.082 0.158

• 0.228, 0.392
• 0.309

0.104

• 0.512, -0.105

Sibling 3 (ref) 0.000 Group Size 4

• 0.026

0.009

• 0.044, -0.008

5

• 0.056

0.017

• 0.089, -0.024

6

• 0.082

0.026

• 0.133, -0.031

7

• 0.084

0.036

• 0.155, -0.013

N 107,510 107,510

SLIDE 40

TABLE S9. Results: Relationship Between Subsequent Birth Interval and Height for Swedish Men Born 1962-1979. Estimates for Age at Conscription Test and Year of Conscription Test Not Shown.

Within-family Between-family Beta SE 95% CI Beta SE 95% CI Subsequent 6-12

• 0.062

0.038

• 0.136, 0.011
• 0.103

0.031

• 0.164, -0.041

Interval Length 13-18

• 0.025

0.017

• 0.059, 0.009
• 0.022

0.014

• 0.049, 0.005

19-24

• 0.007

0.015

• 0.036, 0.022

0.025 0.012 0.002, 0.048 25-30 (ref) 0.000 0.000 31-36

• 0.011

0.015

• 0.039, 0.018
• 0.001

0.011

• 0.024, 0.021

37-42

• 0.006

0.016

• 0.036, 0.025
• 0.012

0.012

• 0.036, 0.012

43-48 0.017 0.017

• 0.017, 0.050
• 0.004

0.013

• 0.030, 0.021

49-54 0.000 0.019

• 0.037, 0.037
• 0.011

0.014

• 0.038, 0.016

55-60 0.003 0.020

• 0.036, 0.042
• 0.005

0.015

• 0.035, 0.024

61-66

• 0.022

0.022

• 0.065, 0.020
• 0.021

0.016

• 0.052, 0.011

67-72

• 0.029

0.024

• 0.076, 0.018
• 0.012

0.018

• 0.047, 0.023

73-78

• 0.014

0.026

• 0.065, 0.036
• 0.026

0.019

• 0.064, 0.011

79-84

• 0.050

0.028

• 0.105, 0.004
• 0.039

0.021

• 0.079, 0.001

85-90

• 0.015

0.030

• 0.075, 0.044

0.001 0.022

• 0.042, 0.045

91-96

• 0.018

0.032

• 0.081, 0.045
• 0.056

0.024

• 0.104, -0.009

97+

• 0.020

0.019

• 0.057, 0.017
• 0.027

0.014

• 0.054, 0.000

Birth Order 1 0.033 0.016 0.001, 0.065 0.055 0.007 0.042, 0.068 2 (ref) 0.000 0.000 3

• 0.024

0.019

• 0.061, 0.014
• 0.065

0.011

• 0.087, -0.042

4

• 0.014

0.038

• 0.089, 0.061
• 0.151

0.023

• 0.197, -0.105

5

• 0.088

0.061

• 0.207, 0.032
• 0.165

0.041

• 0.245, -0.084

6

• 0.119

0.089

• 0.294, 0.056
• 0.273

0.061

• 0.393, -0.154

Maternal Age 15-19 0.021 0.026

• 0.030, 0.072
• 0.240

0.013

• 0.266, -0.213

20-24

• 0.006

0.014

• 0.033, 0.020
• 0.124

0.007

• 0.137, -0.110

25-29 (ref) 0.000 0.000 30-34 0.025 0.017

• 0.009, 0.059

0.079 0.010 0.059, 0.099 35-39 0.015 0.046

• 0.074, 0.105

0.068 0.024 0.022, 0.115 40-44 0.028 0.153

• 0.272, 0.329

0.012 0.083

• 0.150, 0.175

45+ 0.200 0.034 0.134, 0.267 Birth Year 1962 0.219 0.687

• 1.127, 1.565

0.647 0.381

• 0.099, 1.393

1963 0.112 0.215

• 0.310, 0.534

0.090 0.139

• 0.182, 0.362

1964 0.211 0.129

• 0.041, 0.463

0.450 0.089 0.275, 0.625 1965 0.180 0.109

• 0.034, 0.394

0.386 0.078 0.233, 0.540 1966 0.111 0.089

• 0.063, 0.284

0.318 0.066 0.189, 0.448 1967 0.140 0.071 0.002, 0.279 0.257 0.056 0.147, 0.367 1968 0.052 0.055

• 0.055, 0.160

0.171 0.045 0.084, 0.258 1969 0.003 0.039

• 0.073, 0.079

0.085 0.033 0.020, 0.151 1970 (ref) 0.000 0.000 1971 0.035 0.036

• 0.036, 0.106
• 0.047

0.031

• 0.107, 0.014

1972

• 0.012

0.050

• 0.110, 0.086
• 0.132

0.042

• 0.213, -0.050

1973

• 0.042

0.061

• 0.162, 0.078
• 0.196

0.050

• 0.295, -0.097

1974

• 0.022

0.073

• 0.164, 0.121
• 0.246

0.059

• 0.362, -0.131

1975

• 0.015

0.083

• 0.178, 0.147
• 0.325

0.067

• 0.457, -0.194

1976 0.035 0.094

• 0.149, 0.219
• 0.286

0.074

• 0.431, -0.141

1977 0.033 0.106

• 0.176, 0.242
• 0.320

0.082

• 0.480, -0.160

1978 0.081 0.119

• 0.153, 0.314
• 0.226

0.089

• 0.400, -0.051

1979 0.034 0.139

• 0.238, 0.307
• 0.245

0.100

• 0.441, -0.050

Sibling 3 (ref) 0.000 Group Size 4

• 0.025

0.009

• 0.043, -0.007

5

• 0.043

0.017

• 0.077, -0.009

6

• 0.094

0.028

• 0.148, -0.040

7

• 0.061

0.037

• 0.134, 0.013

N 113,250 113,250

SLIDE 41

TABLE S10. Results: Relationship Between Preceding Birth Interval and Being Overweight or Obese for Swedish Men Born 1962-1979. Estimates for Age at Conscription Test and Year of Conscription Test Not Shown.

Within-family Between-family Beta SE 95% CI Beta SE 95% CI Preceding 6-12

• 0.015

0.017

• 0.048, 0.018
• 0.008

0.009

• 0.026, 0.010

Interval Length 13-18

• 0.001

0.008

• 0.016, 0.014

0.002 0.004

• 0.006, 0.010

19-24 0.004 0.007

• 0.010, 0.017

0.001 0.004

• 0.006, 0.008

25-30 (ref) 0.000 0.000 31-36 0.014 0.007 0.000, 0.028 0.012 0.004 0.005, 0.019 37-42 0.014 0.008

• 0.001, 0.029

0.013 0.004 0.005, 0.020 43-48 0.004 0.008

• 0.012, 0.020

0.016 0.004 0.008, 0.024 49-54 0.000 0.009

• 0.017, 0.018

0.018 0.005 0.009, 0.027 55-60 0.021 0.010 0.002, 0.040 0.033 0.005 0.023, 0.043 61-66 0.017 0.011

• 0.005, 0.039

0.036 0.006 0.024, 0.047 67-72 0.034 0.013 0.009, 0.059 0.042 0.007 0.029, 0.055 73-78 0.027 0.014

• 0.001, 0.054

0.044 0.007 0.030, 0.059 79-84 0.062 0.016 0.031, 0.093 0.057 0.008 0.040, 0.073 85-90 0.020 0.018

• 0.015, 0.054

0.057 0.010 0.038, 0.076 91-96 0.022 0.020

• 0.018, 0.062

0.075 0.011 0.052, 0.097 97+ 0.039 0.015 0.009, 0.068 0.084 0.007 0.070, 0.098 Birth Order 2 (ref) 0.000 0.000 3 0.007 0.007

• 0.007, 0.021

0.023 0.002 0.019, 0.028 4 0.021 0.014

• 0.007, 0.048

0.050 0.005 0.041, 0.059 5 0.017 0.021

• 0.025, 0.059

0.073 0.008 0.056, 0.089 6 0.041 0.030

• 0.017, 0.099

0.090 0.013 0.064, 0.115 7 0.001 0.039

• 0.075, 0.077

0.122 0.017 0.090, 0.154 Maternal Age 15-19

• 0.011

0.024

• 0.058, 0.036

0.028 0.011 0.006, 0.050 20-24

• 0.006

0.008

• 0.021, 0.009

0.032 0.003 0.027, 0.038 25-29 (ref) 0.000 0.000 30-34

• 0.003

0.007

• 0.017, 0.012
• 0.020

0.003

• 0.025, -0.015

35-39

• 0.004

0.014

• 0.032, 0.024
• 0.026

0.004

• 0.034, -0.018

40-44

• 0.034

0.025

• 0.082, 0.015
• 0.042

0.008

• 0.059, -0.025

45+ 0.101 0.070

• 0.035, 0.238
• 0.063

0.032

• 0.126, 0.000

Birth Year 1962 0.015 0.272

• 0.519, 0.549
• 0.127

0.138

• 0.398, 0.145

1963 0.052 0.094

• 0.133, 0.236
• 0.120

0.048

• 0.215, -0.025

1964

• 0.015

0.060

• 0.132, 0.103
• 0.122

0.028

• 0.178, -0.067

1965

• 0.020

0.052

• 0.122, 0.082
• 0.093

0.026

• 0.143, -0.043

1966 0.002 0.043

• 0.083, 0.086
• 0.064

0.022

• 0.108, -0.021

1967

• 0.023

0.036

• 0.094, 0.047
• 0.056

0.019

• 0.093, -0.020

1968

• 0.019

0.027

• 0.073, 0.035
• 0.043

0.014

• 0.071, -0.015

1969

• 0.020

0.019

• 0.058, 0.018
• 0.031

0.010

• 0.051, -0.011

1970 (ref) 0.000 0.000 1971 0.017 0.018

• 0.018, 0.051

0.031 0.010 0.012, 0.049 1972 0.036 0.024

• 0.012, 0.084

0.054 0.013 0.027, 0.080 1973 0.020 0.030

• 0.039, 0.080

0.059 0.017 0.027, 0.092 1974 0.042 0.036

• 0.029, 0.112

0.080 0.020 0.042, 0.118 1975 0.050 0.041

• 0.031, 0.130

0.098 0.022 0.054, 0.141 1976 0.054 0.047

• 0.038, 0.146

0.098 0.025 0.049, 0.147 1977 0.110 0.054 0.004, 0.217 0.107 0.028 0.052, 0.163 1978 0.127 0.061 0.007, 0.248 0.106 0.031 0.044, 0.167 1979 0.084 0.072

• 0.057, 0.226

0.110 0.036 0.040, 0.181 Sibling 3 (ref) 0.000 Group Size 4

• 0.005

0.003

• 0.010, 0.001

5

• 0.009

0.005

• 0.019, 0.001

6

• 0.018

0.008

• 0.035, -0.002

7

• 0.039

0.010

• 0.060, -0.019

N 102,000 102,000

SLIDE 42

TABLE S11. Results: Relationship Between Subsequent Birth Interval and Be- ing Overweight or Obese for Swedish Men Born 1962-1979. Estimates for Age at Conscription Test and Year of Conscription Test Not Shown.

Within-family Between-family Beta SE 95% CI Beta SE 95% CI Subsequent 6-12 0.014 0.016

• 0.018, 0.045

0.010 0.011

• 0.010, 0.031

Interval Length 13-18

• 0.007

0.007

• 0.021, 0.008

0.005 0.004

• 0.004, 0.013

19-24

• 0.008

0.006

• 0.021, 0.004
• 0.004

0.004

• 0.012, 0.003

25-30 (ref) 0.000 0.000 31-36

• 0.004

0.006

• 0.016, 0.009
• 0.004

0.004

• 0.011, 0.003

37-42

• 0.008

0.007

• 0.021, 0.006
• 0.001

0.004

• 0.009, 0.007

43-48

• 0.001

0.007

• 0.015, 0.013
• 0.002

0.004

• 0.011, 0.006

49-54 0.012 0.008

• 0.004, 0.028

0.002 0.005

• 0.007, 0.012

55-60

• 0.008

0.009

• 0.025, 0.009
• 0.003

0.005

• 0.013, 0.006

61-66 0.000 0.009

• 0.018, 0.019
• 0.002

0.005

• 0.013, 0.008

67-72

• 0.014

0.010

• 0.034, 0.007
• 0.007

0.006

• 0.018, 0.005

73-78 0.012 0.011

• 0.010, 0.033

0.004 0.006

• 0.009, 0.016

79-84

• 0.009

0.012

• 0.032, 0.014
• 0.008

0.007

• 0.021, 0.005

85-90 0.006 0.013

• 0.019, 0.032

0.002 0.007

• 0.012, 0.017

91-96 0.010 0.014

• 0.017, 0.036
• 0.005

0.008

• 0.020, 0.011

97+ 0.000 0.008

• 0.016, 0.016
• 0.002

0.005

• 0.012, 0.007

Birth Order 1 0.023 0.007 0.009, 0.037

• 0.006

0.002

• 0.010, -0.001

2 (ref) 0.000 0.000 3

• 0.004

0.008

• 0.020, 0.012

0.025 0.004 0.017, 0.033 4

• 0.003

0.016

• 0.035, 0.029

0.040 0.008 0.024, 0.055 5

• 0.018

0.026

• 0.069, 0.033

0.051 0.014 0.023, 0.078 6 0.005 0.038

• 0.069, 0.080

0.072 0.020 0.032, 0.111 Maternal Age 15-19 0.012 0.011

• 0.010, 0.034

0.065 0.005 0.056, 0.074 20-24 0.007 0.006

• 0.004, 0.018

0.030 0.002 0.026, 0.034 25-29 0.000 0.000 30-34

• 0.007

0.007

• 0.021, 0.008
• 0.007

0.003

• 0.013, -0.001

35-39

• 0.029

0.020

• 0.067, 0.010

0.004 0.008

• 0.011, 0.019

40-44

• 0.019

0.065

• 0.145, 0.108

0.017 0.030

• 0.041, 0.075

45+

• 0.085

0.006

• 0.097, -0.074

Birth Year 1962

• 0.071

0.279

• 0.619, 0.476
• 0.024

0.157

• 0.332, 0.284

1963

• 0.093

0.091

• 0.270, 0.085
• 0.035

0.045

• 0.123, 0.053

1964

• 0.023

0.054

• 0.128, 0.083
• 0.053

0.027

• 0.106, 0.001

1965

• 0.002

0.046

• 0.091, 0.087
• 0.026

0.025

• 0.075, 0.023

1966 0.017 0.037

• 0.056, 0.089
• 0.021

0.021

• 0.063, 0.021

1967 0.017 0.030

• 0.041, 0.075
• 0.009

0.018

• 0.045, 0.027

1968 0.016 0.023

• 0.029, 0.061
• 0.008

0.014

• 0.036, 0.020

1969 0.030 0.016

• 0.002, 0.062

0.010 0.011

• 0.012, 0.031

1970 (ref) 0.000 0.000 1971 0.002 0.015

• 0.027, 0.032

0.016 0.009

• 0.002, 0.035

1972 0.010 0.021

• 0.031, 0.052

0.025 0.013

• 0.001, 0.051

1973 0.021 0.026

• 0.030, 0.072

0.044 0.016 0.013, 0.075 1974 0.035 0.031

• 0.025, 0.095

0.065 0.019 0.028, 0.101 1975 0.053 0.035

• 0.015, 0.122

0.081 0.021 0.040, 0.122 1976 0.055 0.040

• 0.022, 0.133

0.067 0.024 0.020, 0.113 1977 0.059 0.045

• 0.030, 0.148

0.071 0.027 0.018, 0.123 1978 0.060 0.051

• 0.040, 0.160

0.069 0.029 0.012, 0.127 1979 0.064 0.060

• 0.054, 0.181

0.053 0.034

• 0.013, 0.119

Sibling 3 (ref) 0.000 Group Size 4

• 0.004

0.003

• 0.010, 0.001

5

• 0.004

0.005

• 0.014, 0.006

6

• 0.004

0.009

• 0.021, 0.014

7

• 0.033

0.010

• 0.053, -0.013

N 108,024 108,024

SLIDE 43

TABLE S12. Results: Relationship Between Preceding Birth Interval and Be- ing Underweight or Severely Underweight for Swedish Men Born 1962-1979. Estimates for Age at Conscription Test and Year of Conscription Test Not Shown.

Within-family Between-family Beta SE 95% CI Beta SE 95% CI Preceding 6-12

• 0.015

0.014

• 0.042, 0.012
• 0.007

0.008

• 0.021, 0.008

Interval Length 13-18

• 0.006

0.006

• 0.018, 0.007

0.005 0.004

• 0.002, 0.012

19-24

• 0.003

0.006

• 0.014, 0.008
• 0.004

0.003

• 0.009, 0.002

25-30 (ref) 0.000 0.000 31-36

• 0.001

0.006

• 0.013, 0.010

0.001 0.003

• 0.005, 0.007

37-42 0.003 0.006

• 0.010, 0.015

0.003 0.003

• 0.004, 0.009

43-48

• 0.001

0.007

• 0.014, 0.012
• 0.005

0.003

• 0.011, 0.002

49-54 0.000 0.007

• 0.015, 0.014

0.004 0.004

• 0.004, 0.011

55-60 0.010 0.008

• 0.006, 0.025
• 0.002

0.004

• 0.010, 0.006

61-66

• 0.005

0.009

• 0.023, 0.013
• 0.011

0.004

• 0.020, -0.003

67-72 0.004 0.010

• 0.017, 0.024

0.003 0.005

• 0.007, 0.013

73-78 0.015 0.011

• 0.008, 0.037

0.009 0.006

• 0.003, 0.020

79-84 0.017 0.013

• 0.008, 0.042
• 0.003

0.006

• 0.015, 0.009

85-90 0.003 0.014

• 0.026, 0.031
• 0.009

0.007

• 0.022, 0.004

91-96 0.004 0.017

• 0.028, 0.037
• 0.025

0.007

• 0.038, -0.012

97+ 0.003 0.013

• 0.021, 0.028
• 0.011

0.005

• 0.020, -0.002

Birth Order 2 (ref) 0.000 0.000 3 0.010 0.006

• 0.002, 0.021
• 0.002

0.002

• 0.006, 0.002

4 0.006 0.011

• 0.016, 0.028
• 0.008

0.004

• 0.015, -0.001

5

• 0.004

0.018

• 0.038, 0.031
• 0.025

0.007

• 0.038, -0.012

6 0.003 0.024

• 0.044, 0.051
• 0.032

0.011

• 0.054, -0.011

7 0.000 0.032

• 0.063, 0.062
• 0.054

0.014

• 0.081, -0.026

Maternal Age 15-19 0.000 0.019

• 0.038, 0.038
• 0.013

0.009

• 0.030, 0.005

20-24

• 0.005

0.006

• 0.017, 0.007
• 0.005

0.002

• 0.009, 0.000

25-29 (ref) 0.000 0.000 30-34 0.006 0.006

• 0.005, 0.018

0.003 0.002

• 0.001, 0.008

35-39 0.021 0.012

• 0.002, 0.044

0.013 0.003 0.006, 0.019 40-44 0.070 0.020 0.031, 0.110 0.026 0.007 0.012, 0.040 45+ 0.083 0.057

• 0.029, 0.195

0.006 0.024

• 0.042, 0.054

Birth Year 1962 0.000 0.223

• 0.437, 0.438
• 0.080

0.028

• 0.135, -0.026

1963

• 0.052

0.077

• 0.203, 0.099

0.009 0.039

• 0.067, 0.084

1964

• 0.057

0.049

• 0.153, 0.040
• 0.016

0.024

• 0.063, 0.030

1965

• 0.021

0.043

• 0.105, 0.062
• 0.012

0.021

• 0.053, 0.029

1966

• 0.026

0.035

• 0.095, 0.043
• 0.010

0.018

• 0.045, 0.025

1967

• 0.034

0.029

• 0.092, 0.024
• 0.016

0.015

• 0.045, 0.014

1968

• 0.038

0.022

• 0.082, 0.006
• 0.008

0.012

• 0.031, 0.015

1969

• 0.008

0.016

• 0.039, 0.023

0.001 0.009

• 0.016, 0.019

1970 (ref) 0.000 0.000 1971 0.009 0.014

• 0.019, 0.037

0.009 0.008

• 0.007, 0.024

1972 0.003 0.020

• 0.036, 0.043

0.020 0.011 0.000, 0.041 1973 0.010 0.025

• 0.039, 0.058

0.022 0.013

• 0.003, 0.047

1974 0.011 0.029

• 0.047, 0.068

0.012 0.015

• 0.017, 0.042

1975 0.019 0.034

• 0.047, 0.085

0.009 0.017

• 0.024, 0.042

1976 0.018 0.039

• 0.058, 0.093

0.002 0.019

• 0.034, 0.039

1977 0.001 0.044

• 0.086, 0.088

0.001 0.021

• 0.040, 0.042

1978 0.013 0.050

• 0.086, 0.112

0.016 0.023

• 0.028, 0.060

1979 0.031 0.059

• 0.085, 0.147

0.031 0.025

• 0.019, 0.080

Sibling 3 (ref) 0.000 Group Size 4 0.001 0.002

• 0.003, 0.006

5 0.020 0.004 0.012, 0.029 6 0.022 0.007 0.008, 0.036 7 0.048 0.010 0.027, 0.068 N 102,000 102,000

SLIDE 44

TABLE S13. Results: Relationship Between Subsequent Birth Interval and Be- ing Underweight or Severely Underweight for Swedish Men Born 1962-1979. Estimates for Age at Conscription Test and Year of Conscription Test Not Shown.

Within-family Between-family Beta SE 95% CI Beta SE 95% CI Subsequent 6-12 0.010 0.014

• 0.017, 0.036
• 0.006

0.008

• 0.022, 0.011

Interval Length 13-18

• 0.003

0.006

• 0.015, 0.009
• 0.001

0.004

• 0.008, 0.006

19-24 0.004 0.005

• 0.006, 0.014

0.002 0.003

• 0.005, 0.008

25-30 (ref) 0.000 0.000 31-36

• 0.005

0.005

• 0.015, 0.006

0.000 0.003

• 0.006, 0.006

37-42

• 0.001

0.006

• 0.013, 0.010

0.004 0.003

• 0.003, 0.010

43-48

• 0.006

0.006

• 0.018, 0.007

0.004 0.004

• 0.003, 0.011

49-54

• 0.011

0.007

• 0.024, 0.002

0.002 0.004

• 0.005, 0.009

55-60

• 0.006

0.007

• 0.020, 0.009

0.002 0.004

• 0.006, 0.010

61-66

• 0.011

0.008

• 0.026, 0.005

0.001 0.004

• 0.008, 0.009

67-72

• 0.005

0.009

• 0.023, 0.012
• 0.001

0.005

• 0.010, 0.008

73-78

• 0.015

0.009

• 0.034, 0.003
• 0.006

0.005

• 0.016, 0.003

79-84

• 0.008

0.010

• 0.028, 0.012
• 0.001

0.005

• 0.011, 0.010

85-90 0.003 0.011

• 0.019, 0.025

0.007 0.006

• 0.005, 0.019

91-96

• 0.010

0.012

• 0.032, 0.013
• 0.002

0.006

• 0.014, 0.010

97+

• 0.010

0.007

• 0.024, 0.003
• 0.004

0.004

• 0.011, 0.003

Birth Order 1

• 0.013

0.006

• 0.025, -0.002

0.007 0.002 0.003, 0.011 2 (ref) 0.000 0.000 3 0.023 0.007 0.009, 0.036 0.004 0.003

• 0.003, 0.011

4 0.031 0.014 0.004, 0.058 0.007 0.007

• 0.006, 0.021

5 0.031 0.022

• 0.012, 0.075
• 0.008

0.011

• 0.031, 0.014

6 0.056 0.032

• 0.007, 0.120
• 0.017

0.018

• 0.052, 0.019

Maternal Age 15-19 0.005 0.010

• 0.014, 0.024
• 0.008

0.003

• 0.015, -0.002

20-24 0.003 0.005

• 0.007, 0.012
• 0.002

0.002

• 0.005, 0.002

25-29 (ref) 0.000 0.000 30-34

• 0.004

0.006

• 0.016, 0.009

0.005 0.003

• 0.001, 0.010

35-39

• 0.016

0.017

• 0.049, 0.016

0.004 0.007

• 0.009, 0.017

40-44 0.082 0.055

• 0.026, 0.190

0.036 0.028

• 0.019, 0.090

45+

• 0.072

0.003

• 0.078, -0.065

Birth Year 1962 0.066 0.239

• 0.402, 0.535
• 0.052

0.026

• 0.104, -0.001

1963

• 0.046

0.078

• 0.198, 0.106

0.023 0.034

• 0.044, 0.090

1964 0.013 0.046

• 0.077, 0.103

0.011 0.023

• 0.034, 0.056

1965 0.012 0.039

• 0.064, 0.089
• 0.002

0.020

• 0.041, 0.037

1966 0.026 0.032

• 0.036, 0.088

0.007 0.018

• 0.027, 0.042

1967 0.019 0.025

• 0.031, 0.068

0.000 0.015

• 0.029, 0.029

1968 0.017 0.020

• 0.021, 0.055

0.003 0.012

• 0.020, 0.026

1969 0.024 0.014

• 0.003, 0.051

0.013 0.009

• 0.005, 0.031

1970 (ref) 0.000 0.000 1971 0.005 0.013

• 0.021, 0.030

0.016 0.007 0.001, 0.030 1972

• 0.011

0.018

• 0.047, 0.024

0.017 0.010

• 0.003, 0.038

1973

• 0.019

0.022

• 0.062, 0.025

0.029 0.012 0.005, 0.053 1974

• 0.025

0.026

• 0.077, 0.026

0.023 0.015

• 0.006, 0.051

1975

• 0.028

0.030

• 0.087, 0.031

0.011 0.017

• 0.022, 0.043

1976

• 0.030

0.034

• 0.097, 0.036

0.015 0.018

• 0.021, 0.051

1977

• 0.026

0.039

• 0.102, 0.050

0.009 0.020

• 0.030, 0.049

1978

• 0.036

0.044

• 0.122, 0.049

0.015 0.022

• 0.028, 0.058

1979

• 0.057

0.051

• 0.157, 0.044

0.038 0.025

• 0.010, 0.086

Sibling 3 (ref) 0.000 Group Size 4

• 0.001

0.002

• 0.005, 0.004

5 0.012 0.004 0.004, 0.021 6 0.007 0.007

• 0.006, 0.021

7 0.029 0.010 0.009, 0.049 N 108,024 108,024

SLIDE 45

TABLE S14. Results: Relationship Between Preceding Birth Interval and Mor- tality for Swedish Men and Women Born 1938-1960.

Within-family Between-family RR SE 95% CI RR SE 95% CI Preceding 6-12 1.01 0.06 0.90-1.14 0.97 0.04 0.89-1.05 Interval Length 13-18 0.96 0.03 0.91-1.02 0.94 0.02 0.91-0.98 19-24 0.97 0.03 0.92-1.02 0.95 0.02 0.92-0.98 25-30 (ref) 1.00 1.00 31-36 0.95 0.03 0.90-1.01 0.98 0.02 0.95-1.02 37-42 0.99 0.03 0.93-1.05 1.00 0.02 0.96-1.04 43-48 1.01 0.03 0.95-1.08 0.98 0.02 0.94-1.02 49-54 1.04 0.04 0.96-1.11 1.01 0.02 0.97-1.06 55-60 0.93 0.04 0.86-1.01 0.94 0.03 0.89-0.99 61-66 0.99 0.04 0.91-1.08 1.00 0.03 0.94-1.05 67-72 1.01 0.05 0.92-1.11 0.99 0.03 0.94-1.05 73-78 0.94 0.05 0.84-1.04 0.97 0.03 0.91-1.04 79-84 0.91 0.06 0.81-1.02 0.98 0.04 0.91-1.05 85-90 0.89 0.07 0.78-1.02 0.93 0.04 0.85-1.01 91-96 0.96 0.08 0.82-1.11 0.90 0.05 0.82-0.98 97+ 0.94 0.05 0.85-1.04 0.85 0.03 0.80-0.90 Gender Men (ref) 1.00 0.00 1.00-1.00 1.00 0.00 1.00-1.00 Women 0.65 0.01 0.63-0.67 0.68 0.01 0.67-0.70 Birth Order 2 (ref) 1.00 0.00 1.00-1.00 1.00 0.00 1.00-1.00 3 1.03 0.02 0.99-1.07 0.91 0.01 0.89-0.93 4 0.98 0.03 0.92-1.05 0.83 0.02 0.80-0.86 5 1.00 0.05 0.91-1.10 0.82 0.03 0.78-0.86 6 1.01 0.06 0.89-1.14 0.80 0.04 0.74-0.87 7 1.04 0.08 0.89-1.21 0.73 0.04 0.67-0.80 Maternal Age 15-19 1.08 0.11 0.87-1.33 1.16 0.06 1.04-1.30 20-24 1.01 0.03 0.95-1.07 1.04 0.01 1.01-1.07 25-29 (ref) 1.00 0.00 1.00-1.00 1.00 0.00 1.00-1.00 30-34 0.97 0.03 0.92-1.03 0.96 0.01 0.94-0.99 35-39 0.97 0.04 0.89-1.06 0.95 0.01 0.93-0.98 40-44 1.07 0.07 0.94-1.21 1.01 0.02 0.97-1.05 45+ 1.03 0.13 0.81-1.33 0.98 0.07 0.85-1.12 Cohort 1938-1940 1.03 0.04 0.94-1.12 0.88 0.02 0.85-0.91 1941-1945 1.03 0.03 0.98-1.09 0.89 0.01 0.87-0.92 1946-1950 (ref) 1.00 0.00 1.00-1.00 1.00 0.00 1.00-1.00 1951-1955 0.98 0.03 0.93-1.04 1.26 0.02 1.22-1.30 1956-1960 0.92 0.05 0.83-1.01 1.75 0.02 1.68-1.82 Sibling 3 (ref) 1.00 0.00 1.00-1.00 Group Size 4 0.83 0.01 0.81-0.84 5 0.72 0.01 0.70-0.74 6 0.64 0.02 0.62-0.66 7 0.55 0.02 0.53-0.58 N 159,554 159,554

SLIDE 46

TABLE S15. Results: Relationship Between Subsequent Birth Interval and Mortality for Swedish Men and Women Born 1938-1960.

Within-family Between-family RR SE 95% CI RR SE 95% CI Subsequent 6-12 1.02 0.06 0.91-1.14 0.92 0.04 0.85-1.00 Interval Length 13-18 1.03 0.03 0.98-1.08 0.95 0.02 0.92-0.99 19-24 1.03 0.03 0.98-1.08 0.98 0.02 0.95-1.02 25-30 (ref) 1.00 0.00 1.00-1.00 1.00 0.00 1.00-1.00 31-36 1.00 0.03 0.95-1.06 1.02 0.02 0.99-1.06 37-42 1.02 0.03 0.96-1.09 1.03 0.02 0.99-1.07 43-48 1.03 0.03 0.97-1.10 1.07 0.02 1.03-1.12 49-54 0.98 0.04 0.91-1.05 1.05 0.02 1.00-1.09 55-60 1.03 0.04 0.95-1.10 1.12 0.02 1.07-1.17 61-66 1.00 0.04 0.93-1.09 1.13 0.03 1.08-1.19 67-72 0.91 0.05 0.84-1.00 1.11 0.03 1.05-1.17 73-78 0.96 0.05 0.88-1.06 1.13 0.03 1.06-1.19 79-84 1.08 0.05 0.98-1.20 1.17 0.03 1.10-1.24 85-90 1.09 0.06 0.98-1.23 1.18 0.03 1.11-1.27 91-96 1.07 0.06 0.95-1.21 1.17 0.04 1.09-1.25 97+ 1.05 0.03 0.98-1.12 1.22 0.02 1.17-1.27 Gender Men (ref) 1.00 0.00 1.00-1.00 1.00 0.00 1.00-1.00 Women 0.64 0.01 0.62-0.66 0.69 0.01 0.68-0.70 Birth Order 1 1.01 0.02 0.97-1.05 1.15 0.01 1.12-1.18 2 (ref) 1.00 0.00 1.00-1.00 1.00 0.00 1.00-1.00 3 1.03 0.02 0.99-1.07 0.92 0.02 0.89-0.95 4 1.00 0.04 0.93-1.07 0.81 0.02 0.78-0.85 5 1.05 0.05 0.94-1.16 0.77 0.03 0.72-0.83 6 1.07 0.07 0.93-1.23 0.72 0.05 0.65-0.80 Maternal Age 15-19 0.97 0.05 0.88-1.07 1.11 0.02 1.06-1.15 20-24 0.99 0.02 0.94-1.04 1.05 0.01 1.03-1.07 25-29 (ref) 1.00 0.00 1.00-1.00 1.00 0.00 1.00-1.00 30-34 0.97 0.03 0.92-1.02 0.98 0.01 0.96-1.01 35-39 0.97 0.05 0.89-1.07 1.01 0.02 0.97-1.04 40-44 1.23 0.10 1.02-1.49 1.19 0.04 1.11-1.29 45+ 0.49 1.13 0.05-4.48 0.53 0.73 0.13-2.20 Cohort 1938-1940 1.12 0.04 1.03-1.21 0.71 0.01 0.69-0.73 1941-1945 1.08 0.03 1.03-1.14 0.80 0.01 0.78-0.82 1946-1950 (ref) 1.00 0.00 1.00-1.00 1.00 0.00 1.00-1.00 1951-1955 0.95 0.03 0.90-1.01 1.46 0.02 1.41-1.50 1956-1960 0.91 0.05 0.82-1.01 2.23 0.02 2.14-2.32 Sibling 3 (ref) 1.00 0.00 1.00-1.00 Group Size 4 0.82 0.01 0.80-0.84 5 0.73 0.01 0.71-0.75 6 0.66 0.02 0.64-0.68 7 0.60 0.02 0.57-0.62 N 150,907 150,907

SLIDE 47

TABLE S16. Preceding Birth Interval: Robustness Checks Using Alternative Specifications of Birth Interval Variable.

Fitness Height Between-family Within-family Between-family Within-family Beta 95% CI Beta 95% CI Beta 95% CI Beta 95% CI Binary 0-24 months (ref) 0.000 0.00 0.000 0.000 >24 months

• 0.051
• 0.066, -0.036

0.011

• 0.015, 0.036
• 0.035
• 0.050, -0.021

0.001

• 0.019, 0.022

Binary 0-18 months (ref) 0.000 0.000 0.000 0.000 >18 months

• 0.032
• 0.053, -0.012

0.005

• 0.028, 0.039
• 0.019
• 0.039, 0.001

0.007

• 0.020, 0.035

Continuous Interval (months)

• 0.002
• 0.002, -0.002

0.000

• 0.001, 0.000
• 0.001
• 0.001, -0.001

0.000 0.000, 0.001 Quadratic Interval (months)

• 0.003
• 0.005, -0.002
• 0.003
• 0.007, 0.001
• 0.002
• 0.003, -0.001

0.000

• 0.004, 0.003

Interval squared 0.000 0.000, 0.000 0.000 0.000, 0.000 0.000 0.000, 0.000 0.000 0.000, 0.000 Underweight Overweight Between-family Within-family Between-family Within-family Beta 95% CI Beta 95% CI Beta 95% CI Beta 95% CI Binary 0-24 months (ref) 0.000 0.00 0.000 0.000 >24 months 0.000

• 0.004, 0.004

0.005

• 0.003, 0.012

0.016 0.011, 0.021 0.006

• 0.003, 0.015

Binary 0-18 months (ref) 0.000 0.000 0.000 0.000 >18 months

• 0.004
• 0.010, 0.001

0.006

• 0.004, 0.016

0.013 0.006, 0.019 0.009

• 0.003, 0.021

Continuous Interval (months) 0.000 0.000, 0.000 0.000 0.000, 0.000 0.001 0.001, 0.001 0.000 0.000, 0.001 Quadratic Interval (months) 0.000 0.000, 0.000 0.000

• 0.001, 0.002

0.000 0.000, 0.001 0.000

• 0.002, 0.001

Interval squared 0.000 0.000, 0.000 0.000 0.000, 0.000 0.000 0.000, 0.000 0.000 0.000, 0.000 Mortality Between-family Within-family RR 95% CI RR 95% CI Binary 0-24 months (ref) 1.00 1.00 >24 months 1.04 1.02-1.06 1.02 0.98-1.05 Binary 0-18 months (ref) 1.00 1.00 >18 months 1.03 1.00-1.06 1.01 0.97-1.05 Continuous Interval (months) 1.00 1.00-1.00 1.00 1.00-1.00 Quadratic Interval (months) 1.00 1.00-1.00 1.00 1.00-1.00 Interval squared 1.00 1.00-1.00 1.00 1.00-1.00

SLIDE 48

TABLE S17. Subsequent Birth Interval: Robustness Checks Using Alternative Specifications of Birth Interval Variable.

Fitness Height Between-family Within-family Between-family Within-family Beta 95% CI Beta 95% CI Beta 95% CI Beta 95% CI Binary 0-24 months (ref) 0.000 0.00 0.000 0.000 >24 months

• 0.003
• 0.018, 0.012
• 0.011
• 0.037, 0.016
• 0.011
• 0.026, 0.004

0.011

• 0.011, 0.032

Binary 0-18 months (ref) 0.000 0.000 0.000 0.000 >18 months 0.019

• 0.003, 0.041
• 0.009
• 0.044, 0.026

0.028 0.007, 0.050 0.024

• 0.004, 0.052

Continuous Interval (months) 0.000 0.000, 0.000 0.000 0.000, 0.000 0.000 0.000, 0.000 0.000 0.000, 0.000 Quadratic Interval (months) 0.000

• 0.001, 0.000

0.000

• 0.001, 0.001

0.000

• 0.001, 0.000

0.000

• 0.001, 0.001

Interval squared 0.000 0.000, 0.000 0.000 0.000, 0.000 0.000 0.000, 0.000 0.000 0.000, 0.000 Underweight Overweight Between-family Within-family Between-family Within-family Beta 95% CI Beta 95% CI Beta 95% CI Beta 95% CI Binary 0-24 months (ref) 0.000 0.00 0.000 0.000 >24 months 0.001

• 0.003, 0.005
• 0.005
• 0.013, 0.002
• 0.001
• 0.006, 0.004

0.005

• 0.004, 0.014

Binary 0-18 months (ref) 0.000 0.000 0.000 0.000 >18 months 0.003

• 0.003, 0.008

0.001

• 0.009, 0.011
• 0.007
• 0.014, 0.000

0.000

• 0.012, 0.012

Continuous Interval (months) 0.000 0.000, 0.000 0.000 0.000, 0.000 0.000 0.000, 0.000 0.000 0.000, 0.000 Quadratic Interval (months) 0.000 0.000, 0.000 0.000

• 0.001, 0.000

0.000 0.000, 0.000 0.000 0.000, 0.001 Interval squared 0.000 0.000, 0.000 0.000 0.000, 0.000 0.000 0.000, 0.000 0.000 0.000, 0.000 Mortality Between-family Within-family RR 95% CI RR 95% CI Binary 0-24 months (ref) 1.00 1.00 >24 months 1.10 1.08-1.12 0.98 0.95-1.01 Binary 0-18 months (ref) 1.00 1.00 >18 months 1.10 1.07-1.12 0.99 0.95-1.03 Continuous Interval (months) 1.00 1.00-1.00 1.00 1.00-1.00 Quadratic Interval (months) 1.00 1.00-1.00 1.00 1.00-1.00 Interval squared 1.00 1.00-1.00 1.00 1.00-1.00