Different effects of blood pressure on mortality from stroke subtypes depending on BMI levels: a 19-year cohort study in the Japanese general population--NIPPON DATA80.

To evaluate the relationship between blood pressure and cerebrovascular death depending on body mass index (BMI) levels, we analysed a database of 9338 subjects from the National Integrated Project for Prospective Observation of Non-communicable Disease and its Trends in the Aged, which was originally conducted a baseline survey in 1980 and followed up in 1999. Relative risk (RR) and a 95% confidence interval (CI) of death from total stroke, cerebral infarction, and intracerebral haemorrhage after adjusting for age, sex, serum cholesterol, albumin, glucose, the use of antihypertensive agents, a past history of diabetes, BMI, smoking, and drinking were estimated with the Cox-proportional hazard model in the BMI tertile groups of a representative Japanese population. Cutoff points of BMI tertiles are 21.2 and 23.8 kg/m2. The results indicated that a 10 mmHg systolic blood pressure (SBP) increase was associated with mortality from intracerebral haemorrhage at low and middle BMI groups (RR= 1.38 and 1.23; 95% CI=1.17-1.62 and 1.03-1.47, respectively). SBP was positively associated with mortality from cerebral infarction in middle and high BMI groups (RR=1.19 and 1.21; 95% CI=1.06-1.33 and 1.06-1.38, respectively). The effects of diastolic blood pressure on intracerebral haemorrhage and infarction had the same tendency as those of SBP. These results suggested that the causal effect of blood pressure on stroke subtypes might be modified by BMI.