Objective: To examine the associations of body mass index (BMI) and weight change with risk of stroke in women.
Setting and design: Prospective cohort study among US female registered nurses participating in the Nurses' Health Study.
Participants: A total of 116759 women aged 30 to 55 years in 1976 who were free from diagnosed coronary heart disease, stroke, and cancer.
Main outcome measure: Incidence of ischemic stroke, hemorrhagic stroke (subarachnoid or intraparenchymal hemorrhage), and total stroke.
Results: During 16 years of follow-up, 866 total strokes (including 403 ischemic strokes and 269 hemorrhagic strokes) were documented. In multivariate analyses adjusted for age, smoking, postmenopausal hormone use, and menopausal status, women with increased BMI (> or =27 kg/m2) had significantly increased risk of ischemic stroke, with relative risks (RRs) of 1.75 (95% confidence interval [CI], 1.17-2.59) for BMI of 27 to 28.9 kg/m2; 1.90 (95% CI, 1.28-2.82) for BMI of 29 to 31.9 kg/m2; and 2.37 (95% CI, 1.60-3.50) for BMI of 32 kg/m2 or more (P for trend<.001), as compared with those with a BMI of less than 21 kg/m2. For hemorrhagic stroke there was a nonsignificant inverse relation between obesity and hemorrhagic stroke, with the highest risk among women in the leanest BMI category (P for trend=.20). For total stroke the RRs were somewhat attenuated compared with those for ischemic stroke but remained elevated for women with higher BMI (P for trend<.001). In multivariate analyses that also adjusted for BMI at age 18 years, weight gain from age 18 years until 1976 was associated with an RR for ischemic stroke of 1.69 (95% CI, 1.26-2.29) for a gain of 11 to 19.9 kg and 2.52 (95% CI, 1.80-3.52) for a gain of 20 kg or more (P for trend<.001), as compared with women who maintained stable weight (loss or gain <5 kg). Although weight change was not related to risk of hemorrhagic stroke (P for trend=.20), a direct relationship was observed between weight gain and total stroke risk (P for trend<.001).
Conclusions: These prospective data indicate that both obesity and weight gain in women are important risk factors for ischemic and total stroke but not hemorrhagic stroke. The relationship between obesity and total stroke depends on the distribution of stroke subtypes in the population.