Previous studies have shown that risk factors commonly associated with coronary disease, stroke, and other vascular disorders also predict dementia. We investigated the longitudinal relationship between body mass index (BMI, calculated as weight in kilograms divided by the square of height in meters) and risk of hospital discharge or death certificate diagnosis of dementia.
A total of 7402 men who were 47 to 55 years old in 1970 to 1973, without prior stroke or myocardial infarction, derived from a population sample of 9998 men were prospectively followed up until 1998. Two hundred fifty-four men (3.4%) had a hospital discharge diagnosis or a death certificate diagnosis of dementia: 176 with a primary diagnosis or cause of death and 78 with a secondary diagnosis.
The relationship between BMI and dementia as a primary diagnosis was J-shaped, and men with a BMI between 20.00 and 22.49 had the lowest risk. Subsequently, after adjustment for smoking, blood pressure, serum cholesterol level, diabetes mellitus, and social class, the risk increased linearly in men who had a BMI of 22.50 to 24.99 (multiple-adjusted hazard ratio [HR], 1.73; 95% confidence interval [CI], 0.92-3.25), 25.00 to 27.49 (HR, 1.93; 95% CI, 1.03-3.63), 27.50 to 29.99 (HR, 2.30; 95% CI, 1.18-4.47), and 30.00 or greater (HR, 2.54; 95% CI, 1.20-5.36) (P for linear trend = .03). Men with a BMI less than 20.00 had a nonsignificantly elevated risk (HR, 2.19; 95% CI, 0.77-6.25).
A J-shaped relationship was observed between BMI and dementia, such that a BMI less than 20 and an increasing BMI of 22.5 or greater were associated with increased risk from midlife to old age of a primary hospital diagnosis of dementia. Overweight and obesity could be major preventable factors in the development of dementia.