Influence of smoking combined with another risk factor on the risk of mortality from coronary heart disease and stroke: pooled analysis of 10 Japanese cohort studies.

BACKGROUND: In spite of the importance of a multifactorial approach to preventing cardiovascular disease in smokers, most information on the combined adverse effects of smoking and hypertension or high serum cholesterol on cardiovascular disease has been derived from Western populations, and coronary heart disease was often used as the only endpoint. Therefore, the present large-scale pooled analysis attempted to provide reliable information on the adverse effects of the coexistence of smoking and hypertension or high serum cholesterol on the risk of mortality from coronary heart disease and stroke in both, individuals and the entire population in Japan.

METHODS: A total of 27,385 male and 39,207 female participants aged 40-89 years were enrolled from 10 well-qualified Japanese cohort studies with a mean follow-up of 10.1 years. Hazard ratios and their corresponding 95% confidence intervals in smokers who had hypertension or high serum cholesterol were estimated for men and women separately using a Cox proportional hazards regression model that included age, body mass index, cohort and either serum total cholesterol or systolic blood pressure as covariates. Fractions of deaths attributable to the coexistence of these risk factors were also calculated.

RESULTS: The multivariate-adjusted hazard ratios in male and female current smokers with hypertension, compared with those with neither factor were 2.57 (95% confidence intervals, 1.51-4.38) and 6.14 (3.49-10.79) for coronary heart disease, and 3.28 (1.89-5.71) and 1.61 (0.81-3.18) for cerebral infarction, respectively. The fractions of deaths attributable to the coexistence of current smoking and hypertension in men and women were 24.6 and 9.6% for coronary heart disease and 28.1 and 2.0% for cerebral infarction, respectively. Smokers with high serum cholesterol were broadly comparable to hypertensive smokers only with respect to coronary mortality risk; the hazard ratios, compared with those with neither factor were 4.19 (2.33-7.53) for men and 3.90 (1.57-9.67) for women. The fraction of coronary deaths attributable to the coexistence of current smoking and high serum cholesterol was 6.3% in men and 2.2% in women. There was no interaction between smoking habit and blood pressure or serum total cholesterol for these two subtypes in both men and women.

CONCLUSIONS: Particular attention should be given to smokers who have concomitant hypertension or high serum cholesterol for preventing deaths due to cardiovascular disease. From a public health perspective in Japan, priority should be given to hypertensive smokers, since this group makes a large contribution to the burden of both coronary and cerebral infarction deaths.