Number of Offspring and Cardiovascular Disease Risk in Men and Women: The Role of Shared Lifestyle Characteristics

Background: Previous studies of number of offspring and cardiovascular disease
(CVD) report conflicting findings. We re-examined this association in both sexes to clarify the role of the cardiometabolic changes which women experience during
pregnancy versus shared lifestyle characteristics.
Methods: We studied 180,626 women and 133,259 men participating in the UK
Biobank cohort who were free of CVD at baseline. CVD events were obtained from
hospital and death registers. Analyses were conducted using Cox proportional hazards
regression.
Results: The incidence rates of overall CVD was 6 per 1,000 person years for women and 9 per 1,000 person years for men. Number of children showed an association with risk of CVD among women, where the adjusted HR (95% CI) was 1.17 (1.07, 1.28) for one, 1.10 (1.03, 1.19) for two, 1.15 (1.06, 1.25) for three and 1.21 (1.08, 1.35) for four or more as compared to none. Number of children was also associated with CVD among men, where the adjusted HR (95% CI) was 1.11 (1.02, 1.21) for one, 1.03 (0.96, 1.11) for two, 1.13 (1.04, 1.22) for three and 1.13 (1.01, 1.26) for four or more as compared to none. There was no evidence of heterogeneity in the associations between sexes (p-value interaction 0.80). Number of offspring showed similar associations with ischaemic heart disease and hypertensive disorders in both sexes.
Conclusions: We observed similar associations between number of offspring and CVD in both sexes. The association among women might therefore be largely explained by unobserved behavioural and life-style characteristics.