Combined Effects of Smoking and Hypercholesterolemia on the Risk of Stroke and Coronary Heart Disease in Japanese: The Hisayama Study

Background: Cigarette smoking is an established risk factor for stroke and coronary heart disease (CHD) in Western countries. However, it is uncertain whether or not smoking raises the risk of stroke in Japanese. We examined the influence of smoking on the development of stroke and CHD and the effects of interactions between smoking and hypercholesterolemia on these outcomes in a general Japanese population. Methods: A total of 2,421 community-dwelling Japanese individuals, aged 40-79 years, with no history of cardiovascular disease, were followed up for 14 years. Results: During the follow-up, 194 total stroke and 112 CHD events occurred. Compared with never smokers, the multivariate-adjusted hazard ratios for the occurrence of total stroke were 1.53 (95% confidence interval = 0.90-2.61) in former smokers, 1.90 (1.18-3.06) in current light smokers (<20 cigarettes/day) and 2.01 (1.11-3.65) in current heavy smokers (>= 20 cigarettes/day). The multivariate-adjusted hazard ratios for the development of CHD were 1.10 (0.56-2.15), 1.88 (1.02-3.47) and 2.31 (1.17-4.57), respectively. In regard to stroke subtypes, current smoking was an independently significant risk factor for ischemic stroke and subarachnoid hemorrhage. Furthermore, the combination of smoking and hypercholesterolemia synergistically increased the risks of total stroke and CHD (all p for interaction <0.05). Conclusion: Our findings suggest that smoking raises the risks of ischemic stroke, subarachnoid hemorrhage and CHD occurrence in the Japanese population, and that this effect is strengthened by hypercholesterolemia. Copyright (C) 2011 S. Karger AG, Basel