Cigarette smoking and risk of coronary heart disease incidence among middle-aged Japanese men and women: the JPHC Study Cohort I.

BACKGROUND: Few data have been available on the sex-specific magnitude of the smoking effect on the risk of coronary heart disease (CHD) in Asia. DESIGN AND METHODS: A population-based prospective cohort study of 19 782 men and 21 500 women aged 40-59 years between 1990-1992 and 2001 was conducted to examine the relationship between smoking status and the risk of CHD. RESULTS: A total of 260 incidences of CHD were confirmed among men, including 174 myocardial infarctions (MI). The numbers among women were 66 and 43, respectively. The multivariate relative risk 95% confidence interval (CI)] for current smokers versus never-smokers in men after adjustment for cardiovascular risk factors, several life style factors and public health centre was 2.85 (1.98, 4.12) for total CHD and 3.64 (2.27, 5.83) for MI. These respective risks in women were 3.07 (1.48, 6.40) and 2.90 (1.18, 7.18). Among men, a dose-dependent relationship was observed between the number of cigarettes and the risk of MI. The population-attributable risk per cent (95% CI) of CHD was 46% (34, 55) in men and 9% (0, 18) in women. Smoking cessation, however, led to a rapid decline in the CHD risk within 2 years. CONCLUSION: Smoking raises the risk of CHD significantly in both sexes of middle-aged Japanese, with large public health significance especially in men. Smoking cessation would have an immediate effect on risk reduction.