Body mass index and stroke incidence in Japanese community residents: The Jichi Medical School (JMS) Cohort Study

BACKGROUND: High body mass index (BMI) has been reported as a risk factor for cardiovascular events in Western countries, while low BMI has been reported as a risk factor for cardiovascular death in Asian countries, including Japan. Although stroke is a major cause of death and disability in Japan, few cohort studies have examined the association between BMI and stroke incidence in Japan. This study aimed to examine the association between BMI and stroke incidence using prospective data from Japanese community residents. METHODS: Data were analyzed from 12,490 participants in the Jichi Medical School Cohort Study. Participants were categorized into five BMI groups: ≤18.5, 18.6–21.9, 22.0–24.9, 25.0–29.9, and ≥30.0 kg/m(2). Multivariate-adjusted hazard ratios (HRs) and 95% confidence intervals (CIs) were calculated using the Cox proportional hazard model. The group with a BMI of 22.0–24.9 kg/m(2) was used as the reference category. RESULTS: During mean follow-up of 10.8 years, 395 participants (207 men and 188 women) experienced stroke, including 249 cerebral infarctions and 92 cerebral hemorrhages. Men with a BMI ≤18.5 kg/m(2) (HR 2.11; 95% CI, 1.17–3.82) and women with a BMI ≥30.0 kg/m(2) (HR 2.25; 95% CI, 1.28–5.08) were at significantly higher risk for all-stroke. Men with a BMI ≤18.5 kg/m(2) were at significantly higher risk for cerebral infarction (HR 2.15; 95% CI, 1.07–4.33). CONCLUSIONS: The association between BMI and stroke incidence observed in this population was different than those previously reported: low BMI was a risk factor for all-stroke and cerebral infarction in men, while high BMI was a risk factor for all-stroke in women.