Fertility histories, social capital, and physiological health: Unravelling the long-term health impacts of reproductive patterns

Population aging and declining fertility rates pose significant challenges to healthcare systems worldwide. This study examines the association between fertility histories and physiological “wear and tear” in post-reproductive adults and investigates whether social capital moderates this relationship.

Methods
Using data from Understanding Society, a UK longitudinal household study, we analysed 5,413 adults (2,808 women and 2,605 men) who provided blood samples during the 2010-2012 Nurse Health Assessment. Participants included women and men aged over 50 years who had completed their fertility histories. Fertility characteristics included the number of children, age at first and last childbirth, and births within a two-year period. Physiological “wear and tear” was measured using the Biological Health Score (BHS) – a composite index incorporating biomarkers from the endocrine, metabolic, cardiovascular, inflammatory/immune, liver, and kidney systems. Social capital was modelled using indicators of social support and social strain from partner, relatives and friends. Sex-stratified generalised additive models tested (1) the association between each fertility history indicator and BHS and (2) interaction between fertility indicators and social capital in predicting BHS

Findings
Among men, parity was not associated with BHS. Among women, we observed a linear association between parity and BHS with higher parity being correlated with worse BHS. Early primiparity (<20 years) and compressed birth intervals (<2 years) are expected to be associated with worse BHS due to increased physiological strain. Better social capital is anticipated to be associated with better BHS and to buffer the effects of fertility characteristics on BHS.

Conclusions

This study contributes to empirical research on how reproductive patterns shape biological ageing and underline the importance of considering sex-specific life course processes when developing public health strategies for ageing populations.