Number of Live Births, Age at the Time of Having a Child, Span of Births and Risk of Dementia: A Population-Based Cohort Study of 253,611 U.K. Women.

The association between birth-related factors and dementia is unclear. We aimed to investigate their association and subsequent risk of dementia in a large-scale follow-up prospective study. This population-based cohort study used data from U.K. Biobank (2006-2010), and the median follow-up was 12.0 years. Multivariable-adjusted Cox proportional hazard models were used to estimate the hazard ratios (HRs) and 95% confidence intervals (CIs) between number of children, age of first live birth, age of last live birth, span of births, and dementia. Restricted cubic spline models were used to quantify dose-response relationships. A total of 253,611 women with mean age (standard deviation) of 56.3 (8.0) years were included. Compared with women with no child, women who had three or more children and first birth at age before 25 years, had elevated risk of all-cause dementia (HR: 1.30, 95% CI: 1.10-1.54), Alzheimer's disease (AD; 1.21, 1.00-1.46), and vascular dementia (VD; 1.59, 1.19-2.13). Also, women with three or more children and the last birth at age before 30 years, had increased risk of all-cause dementia (1.33, 1.11-1.59), AD (1.27, 1.03-1.57), and VD (1.55, 1.12-2.13). Moreover, women who had three or more children in <7 years, had an increased risk of all-cause dementia (1.25, 1.04-1.49). Dose-response relationship showed a lowest risk of dementia at having two children, and having three or more children in 7-9 years. Number of children, age of births, and span of births were all related to risk of dementia. These findings may help developing fertility policies or dementia prevention programs.