Effects of smoking on the mortality of lung cancer in Korean men.

Few studies have examined the effects of smoking on the morbidity and mortality of lung cancer in Korean men. In Korea, where the prevalence of smoking is among the highest in the world, the morbidity and mortality of lung cancer are rapidly escalating. The objectives of this study were to prospectively examine the effects of smoking on lung cancer and to determine the combined effects of the amount, duration and age that smoking was started. The design was a prospective cohort study with a follow-up period of six years (1993-1998). The subjects included a total of 305,687 Korean men from 35 to 64 years of age who received health insurance from the Korea Medical Insurance Corporation and who had biennial medical evaluations in 1992. The main outcome measures were deaths from lung cancer. As a baseline, 58.2% were current cigarette smokers. Between 1993 and 1998, 891 lung cancer events (34.4/100,000 people per year) occurred. In multivariate Cox proportional hazards models controlling for age, exercise and alcohol use, current smoking increased the risk of lung cancer (risk ratio [RR], 5.6; 95% confidence interval [CI], 4.2 - 7.3). There were significant dose-response relationships to the amount, duration of smoking and age that smoking was started. Compared with nonsmokers, the RR from current smokers who smoked 20 cigarettes per day for over 30 years was 8.2 (5.9 - 11.3), the RR from current smokers who smoked for over 30 years and were less then 19 years of age when they started smoking was 7.8 (5.2 - 11.9), and the RR for those who smoke 20 cigarettes per day and were less than 19 years of age when they started smoking was 8.3 (5.9 -11.6). This study demonstrates that in Korea smoking is a major independent risk factor for lung cancer, and that the risk increases with an increased amount, longer duration, and younger starting age.