Joint effect of hypertension and smoking on the risk of cerebral microbleeds among healthy individuals in Japan: The Kashima Scan Study
METHODS: A total of 893 adults were participated in the Kashima Scan Study, an ongoing population-based cohort study investigating age-related brain changes, between December 2005 and November 2010. They underwent 1.5-T brain magnetic resonance imaging and health examination, and answered self-administered questionnaire for lifestyle-related risk factors, including smoking status. After excluding subjects who had history of stroke (n=7), ischemic heart disease (n=26), we performed cross sectional-analysis using data of 860 adults (aged 33-84). Hypertension was defined as systolic blood pressure of >140mmHg and/or diastolic blood pressure of >90mmHg or use of antihypertensive medication. Subjects were divided into three groups (no MBs, deep MBs and lobar MBs), and associations between MBs and hypertension, smoking status, and their joint effects were assessed by logistic regression. Biologic interaction was estimated with the synergy index.
RESULTS : After adjustment for possible confounders, age and systolic and diastolic blood pressures were found to be associated with the presence of MBs in a dose-dependent manner, especially in the case of deep MBs. Current smoking status was significantly associated with deep MBs, and the odds ratio was 2.73 (95% confidence interval (CI) 1.15–6.48). We found that hypertension and current smoking status had joint effects on the risk of MBs with synergistic additive action (synergy index, 6.30; 95% CI 1.07–37.13).
CONCLUSIONS: These results suggest that approaches combining lowering blood pressure and smoking cessation may greatly reduce the risk of MBs and contribute to preventing stroke.