An Early and Unequal Decline: Life Course Trajectories of Cognitive Aging in the United States.

Cognitive aging is a lifelong process with implications for Alzheimer's disease and dementia. This study aims to fill major gaps in research on the natural history of and social disparities in aging-related cognitive decline over the life span. We conducted integrative data analysis of four large U.S. population-based longitudinal studies of individuals aged 12 to 105 followed over two decades and modeled age trajectories of cognitive function in multiple domains. We found evidence for the onset of cognitive decline in the 4 decade of life, varying gender differences with age, and persistent disadvantage among non-Hispanic Blacks, Hispanics, and those without college education. We further found improvement in cognitive function across 20 century birth cohorts but widening social inequalities in more recent cohorts. These findings advance an understanding of early life origins of dementia risk and invite future research on strategies for promoting cognitive health for all Americans.