Methods: Prospective cohort study among 21414 US male physicians participating in the Physicians' Health Study. Incidence of total, ischemic, and hemorrhagic stroke was measured by self-report and confirmed by medical record review. We used Cox proportional hazards models to evaluate the association of body mass index (BMI), calculated as self-reported weight in kilograms divided by the square of the height in meters, with risk of total, ischemic, and hemorrhagic stroke.

Results: During 12.5 years of follow-up, 747 strokes (631 ischemic, 104 hemorrhagic, and 12 undefined) occurred. Compared with participants with BMIs less than 23, those with BMIs of 30 or greater had an adjusted relative risk of 2.00 (95% confidence interval [CI], 1.48-2.71) for total stroke, 1.95 (95% CI, 1.39-2.72) for ischemic stroke, and 2.25 (95% CI 1.01-5.01) for hemorrhagic stroke. When BMI was evaluated as a continuous variable, each unit increase of BMI was associated with a significant 6% increase in the adjusted relative risks of total (95% CI 4%-8%), ischemic (95% CI 3%-8%), and hemorrhagic stroke (95% CI 1%-12%). Additional adjustment for hypertension, diabetes mellitus, and hypercholesterolemia slightly attenuated the risks for total and ischemic (relative risk, 4%; 95% CI 2%-7%), but not hemorrhagic, stroke.

Conclusions: These prospective data indicate a significant increase in the relative risk of total stroke and its 2 major subtypes with each unit increase of BMI that is independent of the effects of hypertension, diabetes, and cholesterol. Because BMI is a modifiable risk factor, the prevention of stroke may be another benefit associated with preventing obesity in adults.