BACKGROUND: The extent to which cognition in late midlife is influenced by lifetime obesity is unclear. OBJECTIVE: We examined the association between body mass index (BMI) over the adult life course and cognition in late midlife and assessed the cumulative effects of obesity and underweight. DESIGN: Data from the Whitehall II Study were examined. BMI at 25 y (early adulthood) was self-reported at phase 1 and was measured in early midlife (mean age = 44 y; phase 1) and in late midlife (mean age = 61 y; phase 7). Cognition (n = 5131) was assessed in late midlife (phase 7) by using the Mini-Mental State Examination and tests of memory and executive function, all of which were standardized to T scores (mean +/- SD: 50 +/- 10). RESULTS: Both underweight and obesity were associated with lower cognition in late midlife and with early adulthood, early midlife, and late midlife measures of BMI. Being obese at 2 or 3 occasions was associated with lower Mini-Mental State Examination scores and scores of memory and executive function in analyses adjusted for age, sex, and education difference (95 CI) in mean T scores compared with normal-weight group: -1.51 (-2.77, -0.25), -1.27 (-2.46, -0.07), and -1.35 (-2.45, -0.24), respectively. Participants who were underweight at > or =2 occasions from early adulthood to late midlife had lower executive function difference (95 CI) in mean T score: -4.57 (-6.94, -2.20). A large increase in BMI from early to late midlife was associated with lower executive function. CONCLUSIONS: Long-term obesity and long-term underweight in adulthood are associated with lower cognitive scores in late midlife. Public health messages should promote a healthy weight at all ages.
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