Stroke Risk Due to Smoking Characterized by Sex Differences in Japan: The Jichi Medical School Cohort Study

Abstract

Objectives: Smoking is a risk factor for stroke. The relationship between smoking and the risk of different subtypes of stroke has not been fully elucidated. We investigated the relationship between smoking and the incidence of stroke in the Japanese population.

Materials and methods: This prospective, population-based cohort study included 11,324 participants (4447 men; 6877 women) from 12 districts in Japan, between April 1992 and July 1995. Participants were stratified according to smoking status (non-smoker [never smoked]/ex-smoker/current smoker). Male current smokers were further stratified according to the number of cigarettes smoked per day (1-14, 15-29, or ≥ 30). The non-smoking group was used as a reference. Cox proportional hazards analysis was used to determine the risk of stroke due to smoking.

Results: Four hundred and seventeen new stroke events (212 men; 205 women) were recorded during a mean follow-up of 10.7 years, including 95 intracerebral hemorrhages (48 men; 47 women), 267 cerebral infarctions (152 men; 115 women), and 54 subarachnoid hemorrhages (12 men; 42 women). In multivariable analysis, the hazard ratios (95% confidence intervals) for male current smokers (≥ 30 cigarettes/day) were 1.89 (1.08-3.31) and 3.41 (1.22-9.57) for all strokes and intracerebral hemorrhages, respectively; those for female current smokers were 2.78 (1.62-4.74), 3.14 (1.51-6.54), and 4.03 (1.64-9.93) for all strokes, cerebral infarctions, and subarachnoid hemorrhages, respectively.

Conclusions: Smoking ≥ 30 cigarettes/day is a risk factor for stroke, especially intracerebral hemorrhage in men. Furthermore, smoking increases the risk of cerebral infarction and subarachnoid hemorrhage in women.

Keywords: Cohort Study; Japanese population; Proportional hazards model; Risk factor; Smoking; Stroke.