Background  Overweight and obesity are epidemic in Western societies and constitute a major public health problem because of adverse effects on vascular health. Vascular factors may play a role in the development of a rapidly growing disease of late life, Alzheimer disease (AD). Using body mass index (BMI, calculated as weight in kilograms divided by the square of height in meters), we examined whether overweight is a risk factor for dementia and AD.

Methods  The relationship between BMI and dementia risk was investigated in a representative cohort of 392 nondemented Swedish adults who were followed up from age 70 to 88 years, with the use of neuropsychiatric, anthropometric, and other measurements. Multivariate Cox proportional hazards regression analyses included BMI, blood pressure, cardiovascular disease, cigarette smoking, socioeconomic status, and treatment for hypertension.

Results:  During the 18-year follow-up (4184.8 risk-years), 93 participants were diagnosed as having dementia. Women who developed dementia between ages 79 and 88 years were overweight, with a higher average BMI at age 70 years (27.7 vs 25.7; P = .007), 75 years (27.9 vs 25.0; P<.001), and 79 years (26.9 vs 25.1; P = .02) compared with nondemented women. A higher degree of overweight was observed in women who developed AD at 70 years (29.3; P = .009), 75 years (29.6; P<.001), and 79 years (28.2; P = .003) compared with nondemented women. For every 1.0 increase in BMI at age 70 years, AD risk increased by 36%. These associations were not found in men.

Conclusions  Overweight is epidemic in Western societies. Our data suggest that overweight at high ages is a risk factor for dementia, particularly AD, in women. This may have profound implications for dementia prevention.