RESUMO
Background: Environmental exposures in early life explain variability in many physiological and behavioural traits in adulthood. Recently, we showed that exposure to a composite marker of low maternal capital explained the clustering of adverse behavioural and physical traits in adult daughters in a Brazilian birth cohort. These associations were strongly mediated by whether or not the daughter had reproduced by the age of 18 years. Using evolutionary life history theory, we attributed these associations to trade-offs between competing outcomes, whereby daughters exposed to low maternal capital prioritised investment in reproduction and defence over maintenance and growth. However, little is known about such trade-offs in sons. Methods: We investigated 2,024 mother-son dyads from the same birth cohort. We combined data on maternal height, body mass index, income, and education into a composite "maternal capital" index. Son outcomes included reproductive status at the age of 18 years, growth trajectory, adult anthropometry, body composition, cardio-metabolic risk, educational attainment, work status, and risky behaviour (smoking, violent crime). We tested whether sons' early reproduction and exposure to low maternal capital were associated with adverse outcomes and whether this accounted for the clustering of adverse outcomes within individuals. Results: Sons reproducing early were shorter, less educated, and more likely to be earning a salary and showing risky behaviour compared to those not reproducing, but did not differ in foetal growth. Low maternal capital was associated with a greater likelihood of sons' reproducing early, leaving school, and smoking. High maternal capital was positively associated with sons' birth weight, adult size, and staying in school. However, the greater adiposity of high-capital sons was associated with an unhealthier cardio-metabolic profile. Conclusion: Exposure to low maternal investment is associated with trade-offs between life history functions, helping to explain the clustering of adverse outcomes in sons. The patterns indicated future discounting, with reduced maternal investment associated with early reproduction but less investment in growth, education, or healthy behaviour. However, we also found differences compared to our analyses of daughters, with fewer physical costs associated with early reproduction. Exposure to intergenerational "cycles of disadvantage" has different effects on sons vs. daughters, hence interventions may have sex-specific consequences.
Assuntos
Coorte de Nascimento , Núcleo Familiar , Adolescente , Adulto , Brasil/epidemiologia , Feminino , Humanos , Masculino , Estudos Prospectivos , Reprodução/fisiologiaRESUMO
Previous research has found that the presence of grandparents, particularly grandmothers, is often positively associated with child survival. Little research has explored the potential mechanisms driving these associations. We use data from rural Guatemala to test whether contact with and direct investment (advice and financial) from grandparents is associated with child health, proxied by height. Our results demonstrate the complexity of family relationships and their influence on child health, suggesting that both cooperative and competitive relationships exist within the family. The clearest evidence we find for grandparental influence is that having a living paternal grandmother tends to be negatively associated with child height. By contrast, contact with maternal kin appears broadly to be beneficial for child height, although these relationships are weaker. These patterns are mirrored in maternal body mass index, suggesting grandparental influence acts partly through maternal health. These findings support the hypotheses that, under conditions of limited resources, family relationships may be competitive within the family lineage which shares the same resource base, but cooperative when there are few costs to cooperation. Finally, financial assistance from maternal grandfathers is positively correlated with infant length but negatively with the height of older children, perhaps because the receipt of financial support is an indication of need. The provision of advice shows no associations with child height.