The Relationship Between Fertility History and Incident Dementia in the U.S. Health and Retirement Study.

OBJECTIVES: An emerging literature suggests that fertility history, which includes measures of parity and birth timing, may influence cognitive health in older ages, especially among women given their differential exposure to pregnancy and sex hormones. Yet, few studies have examined associations between measures of fertility history and incident dementia in population-based samples.

METHOD: We examined the associations between parity, younger age at first birth, and older age at last birth with incident dementia over a 16-year period in a prospective sample of 15,361 men and women aged 51-100 years at baseline drawn from the Health and Retirement Study. We used Cox regression and the Fine and Gray model to obtain cause-specific hazard ratios (csHRs) and subdistribution hazard ratios for incident dementia from gender-stratified models, with the latter method accounting for the semicompeting risk of death.

RESULTS: During the follow-up period (median 13.0 years), the crude incidence rate for dementia was 16.6 and 19.9 per 1,000 person-years for men and women, respectively. In crude models estimating csHRs, higher parity (vs parity 2) and younger age at first birth were associated with increased risk of dementia for both genders. These associations did not persist after adjusting for sociodemographic characteristics, smoking status, and health conditions, with much of the attenuation in estimates occurring after adjustment for sociodemographic characteristics.

DISCUSSION: In this population-based, multiethnic cohort, we observed limited evidence for an association between measures of fertility history and incident dementia among men and women after adjusting for potential confounders.