Association of the number of offspring with risk of cardiovascular disease in men and women: the role of shared lifestyle characteristics

Abstract

BackgroundStudies of number of offspring and cardiovascular disease (CVD) among women report conflicting findings. An assessment of the association between number of offspring and CVD risk in both sexes could clarify whether the association reflects pregnancy-related cardiometabolic changes or shared lifestyle characteristics. We aimed to study the association between number of offspring and cardiovascular disease among both sexes in a large prospective cohort. MethodsWe used data from UK Biobank (180 626 women and 133 259 men without CVD at baseline) to assess the association between number of offspring and CVD (overall and subtypes). Information on CVD events came from national hospital and death registers. Analyses were conducted with Cox regression, adjusting for a large number of covariates including age at baseline. The UK Biobank data collection is approved by the National Health Service National Research Ethics Service (ref 11/NW/0382). FindingsThe number of person-years of follow-up was 1 064 386 for women (CVD rate 6 per 1000) and 774 310 for men (9 per 1000). Number of children was associated with risk of CVD in women (adjusted hazard ratio for one child compared with none 1·17, 95% CI 1·07–1·28; for two 1·10, 1·03–1·19; for three 1·15, 1·06–1·25; for four or more 1·21, 1·08–1·35) and in men (1·11, 1·02–1·21; 1·03, 0·96–1·11; 1·13, 1·04–1·22; 1·13, 1·01–1·26). There was no statistical evidence of heterogeneity in the sex-specific estimates (pinteraction=0·80). Associations were similar for CVD subgroups of ischaemic heart disease and hypertensive disorders. No associations between number of children and cerebrovascular disease were observed in either sex. InterpretationOur results suggest that the association between number of offspring and CVD among women might be largely explained by unmeasured behavioural and lifestyle characteristics, rather than a biological effect of repeated pregnancy. FundingMRC Integrative Epidemiology Unit. MCM and AF are funded by a UK Medical Research Council fellowship (MR/M009351/1). SI is funded by a UK Medical Research Council fellowship (MR/N015177/1).