Declining Incident Dementia Rates Across Four Population-Based Birth Cohorts

Abstract

Abstract Background Incidence rates of dementia appear to be declining in high-income countries according to several large epidemiological studies. We aimed to describe declining incident dementia rates across successive birth cohorts in a U.S. population-based sample and to explore the influences of sex and education on these trends. Methods We pooled data from two community-sampled prospective cohort studies with similar study aims and contiguous sampling regions: the Monongahela Valley Independent Elders Survey (1987–2001) and the Monongahela-Youghiogheny Healthy Aging Team (2006–Ongoing). We identified four decade-long birth cohorts spanning birth years 1902–1941. In an analysis sample of 3,010 participants (61% women, mean baseline age = 75.7 years, mean follow-up = 7.1 years), we identified 257 cases of incident dementia indicated by a Clinical Dementia Rating of 1.0 or higher. We used Poisson regression to model incident dementia rates by birth cohort, age, sex, education, and interactions of Sex × Cohort and Sex × Education. We further examined whether cohort effects varied by education, testing a Cohort × Education interaction and stratifying the models by education. Results Compared to the earliest birth cohort (1902–1911), each subsequent cohort had a significantly lower incident dementia rate (1912–1921: incidence rate ratio [IRR] = 0.655, 95% confidence interval [95% CI] = 0.477–0.899; 1922–1931: IRR = 0.387, 95% CI = 0.265–0.564; 1932–1941: IRR = 0.233, 95% CI = 0.121–0.449). We observed no significant interactions of either sex or education with birth cohort. Conclusions A decline in incident dementia rates was observed across successive birth cohorts independent of sex, education, and age.