Body Mass Index and Incidence of Subarachnoid Hemorrhage in Japanese Community Residents: The Jichi Medical School Cohort Study.

Background: Whereas high body mass index (BMI) is reportedly a risk factor for cardiovascular events in Western countries, low BMI has been reported as a risk factor for cardiovascular death in Asia, including Japan. Although subarachnoid hemorrhage (SAH) is a highly fatal disease and common cause of disability, few cohort studies have examined the associations between BMI and SAH in Japan. This study investigated the associations between BMI and incidence of SAH 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 5 BMI groups: ≤18.5, 18.6-21.9, 22.0-24.9, 25.0-29.9, and ≥30.0 kg/m. Multivariate-adjusted hazard ratios (HR) and 95% confidence intervals (CI) were calculated using Cox proportional hazard model with BMI of 22.0-24.9 kg/m as the reference category.

Results: During the mean follow-up period of 10.8 years, 55 participants (13 men, 42 women) experienced SAH. BMI ≥30.0 kg/m was associated with significantly higher risk for SAH (HR, 5.98; 95% CI, 2.25-15.87). BMI ≤18.5 kg/m showed a nonsignificant tendency toward high risk of SAH (HR, 2.51; 95% CI, .81-7.79).

Conclusions: High BMI was a significant risk factor for SAH. Lower BMI showed a nonsignificant tendency toward higher risk of SAH. Our results suggest a J-shaped association between BMI and risk of SAH incidence.