Abstract P142: Number Of Children Three Or More And Having First Child Before Age 22 Are Linked To Increased Risk Of All-cause Dementia

Abstract

Introduction: Evidence on the association between number of children and risk of all-cause dementia has been discordant, and whether timing of birth and span of birth are related to the risk of dementia is unclear. Hypothesis: Estrogen level maintains high during pregnancy and declines dramatically after giving birth. More times of giving birth means more times of drastic fluctuations of endogenous estrogen. We hypothesized that the times of dramatic estrogen fluctuations in a woman’s life course (indicated by number of children) might be associated with risk of dementia. Methods: We used cohort data from UK Biobank, a large population-based prospective cohort study that recruited 502 649 individuals ages 40– 69, between 2006 and 2010. Cox proportional hazards models were used to estimate hazard ratios (HRs) and 95% confidence intervals (CI) for the associations between number of children (categorized as zero, one, two, three or more) and incident all-cause dementia. We also examined the role of timing of birth and span of birth in the association with dementia. Timing of birth included age of first birth (categorized as <22, 22-25, 26-29, and ≥30 years) and age of last birth (categorized as <26, 26-29, 30-33, ≥34 yeas). Span of birth (the span between age of first birth and age of last birth) was categorized as ≤2, 3-4, 5-6, and >6 years). All HRs were adjusted for race/ethnicity, education level, income, body mass index, smoking status, physical activities, number of leisure activities, hypertension status, diabetes status and baseline age. Results: Overall, 253 169 women were included, and we identified 2426 women with dementia. The median follow-up was 11.9 years. Compared to women with no child, the HRs (95% CI) with incident dementia in women with one, two, three or more children were 0.97 (0.83, 1.13), 0.95 (0.84, 1.07) and 1.17 (1.03, 1.33) respectively. Compared to women who had their first child after age 30 years, those first birth before age 22 years had elevated risk of dementia (HR: 1.25, 95%CI: 1.09-1.44), even after parity was further adjusted (1.19, 1.03-1.37). No association was observed between age of last child, span of birth and incident dementia. Nevertheless, subgroup analysis found that the elevated risk between number of three or more children and dementia was only observed in women with age of last birth less than 30 years (1.31, 1.12-1.53), or span of birth less than seven years (1.24, 1.07-1.44). Conclusions: Women with three or more children was linked to 17% higher risk of dementia compared to those with no child, and women who had their first child before age 22 years had around 20% higher risk of dementia compared to those with first child after age 30. Age of last child and span of birth may moderate the relationship between number of children and risk of dementia.