The effect of number of siblings on adult mortality: Evidence from Swedish registers for cohorts born between 1938 and 1972

Sibling Availability, Sibling Sorting, and Subjective Health Among Chinese Adults

Despite rising numbers of only children in China, little is known about their family dynamics and well-being in adulthood-for example, how often they marry other only children and whether those in siblingless families have worse or better health than others. Theoretical expectations produce opposing predictions: siblings might provide social and emotional support and reduce parental caregiving pressures, but only children might receive more support from parents and grandparents. Using the 2010 China Family Panel Study, we examine marital sorting on Chinese adults' number of siblings and test whether sibling availability and sibling sorting are associated with subjective physical and mental health. Despite general perceptions that China has an exceedingly high prevalence of adults with no siblings that might produce very small families, results demonstrate a low prevalence of siblingless couples (i.e., both spouses are only children). Married adults with no siblings or siblings-in-law have better subjective physical health but similar levels of subjective mental health relative to their counterparts with siblings. The health advantages of siblingless marital unions are greater for rural and female adults. Declining sibling prevalence in China will shape future family demographic dynamics but appears less detrimental to population health than sometimes assumed.

Association of number of siblings with preclinical markers of cardiovascular disease. The cardiovascular risk in Young Finns study

To investigate the association of number of siblings with preclinical cardiovascular disease (CVD) markers in adulthood. The sample comprised 2776 participants (54 % female) from the Cardiovascular Risk in Young Finns Study who had CVD risk factor data measured in childhood in 1980 (aged 3-18 years) and markers of preclinical CVD measured in adulthood. Echocardiography was performed in 2011, and carotid intima-media thickness, carotid distensibility, brachial flow-mediated dilatation, and arterial pulse wave velocity were measured in 2001 or 2007. The association between the number of siblings and preclinical CVD was assessed using generalized linear and logistic regression models. Analyses were stratified by sex as associations differed between sexes. Women with 1 sibling had lower E/e'-ratio (4.9, [95%CI 4.8-5.0]) in echocardiography compared with those without siblings (5.1[4.9-5.2]) and those with ≥2 more siblings (5.1[5.0-5.2]) (P for trend 0.01). Men without siblings had the lowest E/A-ratio (1.4[1.3-1.5]) compared with those with 1 sibling (1.5[1.5-1.5]), or ≥2 siblings (1.5[1.5-1.5]) (P for trend 0.01). Women without siblings had highest left ventricular ejection fraction (59.2 %[58.6-59.7 %]) compared with those with 1 sibling (59.1 %[58.8-59.4 %]), or ≥2 siblings (58.4 %[58.1-58.8 %])(P for trend 0.01). In women, brachial flow-mediated dilatation, a measure of endothelial function, was the lowest among participants with ≥2 siblings (9.4 %[9.0-9.8 %]) compared with those with 1 sibling (10.0 %[9.6-10.3 %]) and those without siblings (10.4 %[9.7-11.0 %])(P for trend 0.03). We observed that number of siblings may be associated with increased risk of heart failure in women. As the associations were somewhat inconsistent in males and females, further research is warranted.

Defining and Identifying Only Children: A Research Note on the Concept and Measurement Illustrated With UK Survey Data

Despite increasing interest in the circumstances and outcomes of only children in the demographic literature, the conceptualization of this group has received limited scholarly attention. This research note argues for greater engagement by demographers and social scientists in the conceptualization and identification of only children by addressing three aims. First, we outline potential definitions of only children, present a framework to guide researchers' decisions, and evaluate whether only children can be reliably identified using the British birth cohort studies. Second, we show that the prevalence estimates are contingent on the timing of measurement in childhood, indicating the need for caution when deriving only-child status from cross-sectional household grid data. Third, we demonstrate that both the size and the characteristics of the only-child group may differ across definitions, highlighting that the accurate operationalization of some definitions is particularly restricted by survey designs that prioritize mothers for data collection on children and families. We argue that researchers interested in sole children's outcomes must choose the most appropriate measure for a given research question and, given that many datasets limit how accurately any indicator of only children can capture the chosen definition, reflect on how the operationalization of their measure might affect the results.

Health outcomes of only children across the life course: An investigation using Swedish register data

Only children (with no full biological siblings) are a growing subgroup in many high-income settings. Previous studies have largely focused on the short-term developmental outcomes of only children, but there is limited evidence on their health outcomes. Using Swedish population register data for cohorts born 1940-75, we compare the health of only children with that of children from multi-child sibling groups, taking into account birth order, family size, and presence of half-siblings. Only children showed lower height and fitness scores, were more likely to be overweight/obese in late adolescence, and experienced higher later-life mortality than those with one or two siblings. However, only children without half-siblings were consistently healthier than those with half-siblings, suggesting that parental disruption confers additional disadvantages. The health disadvantage was attenuated but not fully explained by adjustment for parental characteristics and after using within-family maternal cousin comparison designs.

Sibling group size and BMI over the life course: Evidence from four British cohort studies

Only children, here defined as individuals growing up without siblings, are a small but growing demographic subgroup. Existing research has consistently shown that, on average, only children have higher body mass index (BMI) than individuals who grow up with siblings. How this difference develops with age is unclear and existing evidence is inconclusive regarding the underlying mechanisms. We investigate BMI trajectories for only children and those with siblings up to late adolescence for four British birth cohorts and across adulthood for three cohorts. We use data on BMI from ages 2-63 years (cohort born 1946); 7-55 years (born 1958); 10-46 (born 1970) and 3-17 years (born 2000-2002). Using mixed effects regression separately for each cohort, we estimate the change in BMI by age comparing only children and those with siblings. The results show higher average BMI among only children in each cohort, yet the difference is substantively small and limited to school age and adolescence. The association between sibling status and BMI at age 10/11 is not explained by differential health behaviours (physical activity, inactivity and diet) or individual or family background characteristics in any of the cohorts. Although persistent across cohorts, and despite the underlying mechanism remaining unexplained, the substantively small magnitude of the observed difference and the convergence of the trajectories by early adulthood in all cohorts raises doubts about whether the difference in BMI between only children and siblings in the UK context should be of research or clinical concern. Future research could usefully be directed more at whether only children experience elevated rates of disease, for which high BMI is a risk factor, at different stages of the life course and across contexts.

Association between Number of Siblings and Cardiovascular Risk Factors in Childhood and in Adulthood: The Cardiovascular Risk in Young Finns Study

OBJECTIVE

To determine the association of number of siblings on cardiovascular risk factors in childhood and in adulthood.

STUDY DESIGN

In total, 3554 participants (51% female) from the Cardiovascular Risk in Young Finns Study with cardiovascular disease risk factor data at baseline 1980 (age 3-18 years) and 2491 participants with longitudinal risk factor data at the 2011 follow-up. Participants were categorized by number of siblings at baseline (0, 1, or more than 1). Risk factors (body mass index, physical activity, hypertension, dyslipidemia, and overweight, and metabolic syndrome) in childhood and in adulthood were used as outcomes. Analyses were adjusted for age and sex.

RESULTS

In childhood, participants without siblings had higher body mass index (18.2 kg/m², 95% CI 18.0-18.3) than those with 1 sibling (17.9 kg/m², 95% CI 17.8-18.0) or more than 1 sibling (17.8 kg/m², 95% CI 17.7-17.9). Childhood physical activity index was lower among participants without siblings (SD -0.08, 95% CI -0.16-0.00) compared with participants with 1 sibling (SD 0.06, 95%CI 0.01-0.11) or more than 1 sibling (SD -0.02, 95% CI -0.07-0.03). OR for adulthood hypertension was lower among participants with 1 sibling (OR 0.73, 95% CI 0.54-0.98) and more than 1 sibling (OR 0.71, 95% CI 0.52-0.97) compared with participants with no siblings. OR for obesity was lower among participants with 1 sibling (OR 0.72, 95% CI 0.54-0.95) and more than 1 sibling (OR 0.75, 95% CI 0.56-1.01) compared with those with no siblings.

CONCLUSIONS

Children without siblings had poorer cardiovascular risk factor levels in childhood and in adulthood. The number of siblings could help identify individuals at increased risk that might benefit from early intervention.

Sibling rank and sibling number in relation to cardiovascular disease and mortality risk: a nationwide cohort study

BACKGROUND

The number and rank order of siblings could be of importance for risk of cardiovascular disease and mortality. Previous studies have used only fatal events for risk prediction. We, therefore, aimed to use also non-fatal coronary and cardiovascular events in fully adjusted models.

METHODS

From the Multiple-Generation Register in Sweden, data were used from 1.36 million men and 1.32 million women (born 1932-1960), aged 30-58 years at baseline and with follow-up from 1990 to 2015. Mean age at follow-up was 67 years (range 55-83 years). Fatal and non-fatal events were retrieved from national registers.

RESULTS

Compared with men with no siblings, those with 1-2 siblings had a lower, and those with four or more siblings had a higher adjusted risk of cardiovascular events. Again, compared with men with no siblings, those with more than one sibling had a lower total mortality risk, and those with three or more siblings had an increased risk of coronary events.Correspondingly, compared with women with no siblings those women with three siblings or more had an increased risk of cardiovascular events, and those with two siblings or more had an increased risk of coronary events. Women with one sibling or more were at lower total mortality risk, following full adjustment.

CONCLUSION

Being first born is associated with a favourable effect on non-fatal cardiovascular and coronary events for both men and women. The underlying biological mechanisms for this should be studied in a sociocultural context.

Impact of maternal reproductive factors on cancer risks of offspring: A systematic review and meta-analysis of cohort studies

Background

A number of studies have reported on associations between reproductive factors, such as delivery methods, number of birth and breastfeeding, and incidence of cancer in children, but systematic reviews addressing this issue to date have important limitations, and no reviews have addressed the impact of reproductive factors on cancer over the full life course of offspring.

Methods

We performed a comprehensive search in MEDLINE, and Embase up to January 2020 and Web of Science up to 2018 July, including cohort studies reporting the association between maternal reproductive factors of age at birth, birth order, number of births, delivery methods, and breastfeeding duration and cancer in children. Teams of two reviewers independently extracted data and assessed risk of bias. We conducted random effects meta-analyses to estimate summary relative estimates, calculated absolute differences between those with and without risk factors, and used the GRADE approach to evaluate the certainty of evidence.

Results

For most exposures and most cancers, we found no suggestion of a causal relation. We found low to very low certainty evidence of the following very small possible impact: higher maternal age at birth with adult multiple myeloma and lifetime uterine cervix cancer incidence; lower maternal age at birth with childhood overall cancer mortality (RR = 1.15, 95% CI = 1.01–1.30; AR/10,000 = 1, 95% CI = 0 to 2), adult leukemia and lifetime uterine cervix cancer incidence; higher birth order with adult melanoma, cervix uteri, corpus uteri, thyroid cancer incidence, lifetime lung, corpus uteri, prostate, testis, sarcoma, thyroid cancer incidence; larger number of birth with childhood brain (RR = 1.27, 95% CI = 1.06–1.52; AR/10,000 = 1, 95% CI = 0 to 2), leukemia (RR = 2.11, 95% CI = 1.62–2.75; AR/10,000 = 9, 95% CI = 5 to 14), lymphoma (RR = 4.66, 95% CI = 1.40–15.57; AR/10,000 = 11, 95% CI = 1 to 44) incidence, adult stomach, corpus uteri cancer incidence and lung cancer mortality, lifetime stomach, lung, uterine cervix, uterine corpus, multiple myeloma, testis cancer incidence; Caesarean delivery with childhood kidney cancer incidence (RR = 1.25, 95% CI = 1.01–1.55; AR/10,000 = 0, 95% CI = 0 to 1); and breastfeeding with adult colorectal cancer incidence.

Conclusion

Very small impacts existed between a number of reproductive factors and cancer incidence and mortality in children and the certainty of evidence was low to very low primarily due to observational design.

Is the Family Size of Parents and Children Still Related? Revisiting the Cross-Generational Relationship Over the Last Century

In most developed countries, the fertility levels of parents and children are positively correlated. This article analyzes the strength of the intergenerational transmission of family size over the last century, including a focus on this reproduction in large and small families. Using the large-scale French Family Survey (2011), we show a weak but significant correlation of approximately 0.12–0.15, which is comparable with levels in other Western countries. It is stronger for women than men, with a gender convergence across cohorts. A decrease in intergenerational transmission is observed across birth cohorts regardless of whether socioeconomic factors are controlled, supporting the idea that the family of origin has lost implicit and explicit influence on fertility choices. As parents were adopting the two-child family norm, the number of siblings lost its importance for having two children, but it continues to explain lower parity and, above all, three-child families. This suggests that the third child has increasingly become an “extra child” (beyond the norm) favored by people from large families.

Adolescent social isolation and premature mortality in a Swedish birth cohort

Research shows consistently that social ties are important for longevity, and they may be particularly important during adolescence. An absence of social ties, or social isolation, during adolescence may adversely affect long-term health and wellbeing. While prior research has examined associations between isolation from friends and long-term health, and having no siblings and mortality, no study (of which we are aware) considers jointly both the role of having no friends and no siblings, nor more generally with whom adolescents spend time, and the risk of premature mortality. This paper extends the literature by drawing on data from the Stockholm Birth Cohort Study to examine the association between different types of social isolation during adolescence (i.e., an absence of friends, siblings, and time with other adolescents) and the risk of premature mortality by midlife. Results suggest that having no siblings, being unliked at school, and spending (mostly) no time with other adolescents, increases the risk of premature mortality. The association between being unliked and premature mortality was attenuated by demographic and adolescent characteristics. Consistent with our expectations, net of a robust set of covariates, adolescents who had no siblings and mostly spent no time with other adolescents (i.e., isolates) were the group most vulnerable to premature mortality by midlife. However, this was only true for females.

Companionship Patterns and Emotional States During Social Interactions for Adolescents With and Without Siblings

For decades, researchers and the general public have debated whether children without siblings differ from children with siblings in ways that are meaningful for development. One area that is underexplored in the literature on only children versus children with siblings concerns time use and emotional states in alone time and in social interactions. Resource dilution theory and the prior literature suggests that adolescent only children and adolescents with siblings may differ in some social interactions, such as in time with parents, but not in others, such as in time alone, due to offsetting effects or the universality of certain experiences among adolescents. This study tested these arguments by comparing companionship patterns and four emotional states (happiness, sadness, stress, and meaningfulness) among adolescents (ages 15-18) without siblings (N= 465) and adolescents with siblings (N= 2513) in the nationally representative American Time Use Survey (2003-2017). Relative to adolescents with siblings, adolescents without siblings spent more time alone, similar amounts of time with peers, and more time exclusively with parents. Only children were not as happy when spending time alone and with peers as adolescents with siblings, but their emotions in these settings were not more negative or less meaningful. In most other social interactions, emotional states were similar between adolescents with and without siblings. These findings show that adolescents with and without siblings differed mainly in their companionship patterns within the household and in their levels of happiness when alone and with peers.

Birth Intervals and Health in Adulthood: A Comparison of Siblings Using Swedish Register Data

A growing body of research has examined whether birth intervals influence perinatal 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 between birth-to-birth intervals and a variety of health outcomes in adulthood: for men, height, physical fitness, and the probability of falling into different body mass index categories; and for men and women, mortality. In models that 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 obese, 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, although 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.

Environmental risk factors associated with low birth weight: The case study of the Haifa Bay Area in Israel

BACKGROUND

Low birth weight (LBW) is known to be associated with infant mortality and postnatal health complications. Previous studies revealed strong relationships between LBW rate and several socio-demographic factors, including ethnicity, maternal age, and family income. However, studies of association between LBW rate and environmental risk factors remain infrequent.

STUDY METHODS

We retrieved a geo-referenced data set, containing 7216 individual records of children born in 2015 in the Haifa Bay Area in Israel. Using this dataset, we analysed factors affecting LBW prevalence by applying two alternative techniques: analysis of LBW rates in small census area (SCAs) and more recently developed double kernel density (DKD) relative risk (RR) estimates.

RESULTS

In the SCA models, LBW rate was found to be associated with proximity to petrochemical industries (B=-0.26, 95%CI=-0.30, -0.22), road density (B=0.05, 95%CI=0.02, 0.08), distance to the seashore (B=0.17, 95%CI=0.14, 0.22), PM_2.5 (B=0.06, 95%CI=0.04, 0.09) and NO_x (B=0.10, 95%CI=0.06, 0.13) exposure estimates. Although similar factors emerged in the DKD models as well, in most cases, the effects of these factors in the latter models were found to be stronger: proximity to petrochemical industries (B=-0.48, 95%CI= -0.51, -0.30), road density (B=0.05, 95%CI=0.02, 0.08), distance to the seashore (B=0.24, 95%CI=0.21, 0.27), PM_2.5 (B=0.08, 95%CI=0.05, 0.10) and NO_x (B=0.20, 95%CI=0.17, 0.23) exposure estimates. In addition, elevation above the sea level was found to be statistically significant in spatial dependence models estimated for both DKD and SCA rates (P < 0.01).

CONCLUSION

The analysis revealed an excess LBW rate in residential areas located close to petrochemical industries and a protective effect of seashore proximity and elevation above the sea level on the LBW rate. We attribute the latter finding to the moderating effect of elevated seashore locations on outdoor temperatures during the hot summer season.