A 35-Year Longitudinal Assessment of Cognition and Midlife Depression Symptoms: The Vietnam Era Twin Study of Aging

Objective To determine whether early adult cognitive ability is a risk factor for depressive symptoms in midlife and how genetic and environmental influences explain the association and to examine cross-sectional relationships between depressive symptoms and specific cognitive abilities at midlife. Design A 35-year longitudinal and cross-sectional twin study of cognitive aging. Setting Large multicenter study in the United States. Participants One thousand two hundred thirty-seven male twins aged 51 to 60 years. Measurements At the age of 20 years and midlife, participants completed the same version of a general cognitive ability test (Armed Forces Qualification Test [AFQT]). Midlife testing included an extensive neurocognitive protocol assessing processing speed, verbal memory, visual-spatial memory, working memory, executive function, and visual-spatial ability. Participants completed the Center for Epidemiologic Studies Depression Scale before cognitive testing and provided health and life style information during a medical history interview. Results Lower age 20 AFQT scores predicted higher levels of depressive symptoms at age 55 years (r = −0.16,p Conclusion Results suggest that low cognitive ability is a risk factor for depressive symptoms; this association is partly due to shared genetic influences. Crosssectional analyses indicate that the association between depressive symptoms and performance is not linked to specific cognitive domains.