Background and Purpose—The effect of smoking reduction on cardiovascular disease outcomes has not been studied in Asian populations.

Methods—A total of 475 734 Korean men aged 30 to 58 years, stratified into 9 groups based on smoking status at 2 different time points (1990 and 1992), were followed from 1992 to 2001 for the occurrence of stroke or myocardial infarction (MI) events.

Results—Compared with nonreducing heavy smokers (20 cigarettes/d), those who quit smoking showed significantly lower risks of ischemic stroke, subarachnoid hemorrhage, and MI with hazard ratios (95% confidence intervals [CI]) of 0.66 (0.55 to 0.79), 0.58 (0.38 to 0.90), and 0.43 (0.34 to 0.53), respectively. For hemorrhagic stroke, quitters showed lower risk compared with heavy smokers, but the difference was not statistically significant (hazard ratio 0.82, 95% CI: 0.64 to 1.06). Compared with nonreducing heavy smokers, the risks of all stroke combined and MI among reducers tended to decrease, although the reductions were not statistically significant. The risks of subarachnoid hemorrhage and MI in those who reduced from moderate to light smoking tended to be lower than in nonreducing moderate (10 to 19 cigarettes/d) smokers. The association between the reduction of smoking level and the risk of stroke and MI did not change significantly when the analysis was limited to those whose smoking status in 1992 was maintained up to 1994.

Conclusions—Smoking cessation was associated with a decrease in the risks of ischemic stroke, subarachnoid hemorrhage, and MI. More studies are needed to verify the likely health benefits of reducing smoking.