Purpose: To determine the association between cigarette smoking and the incidence of type 2 diabetes mellitus.
Subjects and methods: We studied 21,068 US male physicians aged 40 to 84 years in the Physicians' Health Study who were initially free of diagnosed diabetes mellitus, cardiovascular disease, and cancer. Information about cigarette smoking and other risk indicators was obtained at baseline. The primary outcome was reported diagnosis of type 2 diabetes mellitus.
Results: During 255,830 person-years of follow-up, 770 new cases of type 2 diabetes mellitus were identified. Smokers had a dose-dependent increased risk of developing type 2 diabetes mellitus: compared with never smokers, the age-adjusted relative risk was 2.1 (95% confidence interval [CI]: 1.7 to 2.6) for current smokers of > or = 20 cigarettes per day, 1.4 (95% CI: 1.0 to 2.0) for current smokers of <20 cigarettes per day, and 1.2 (95% CI: 1.0 to 1.4) for past smokers. After multivariate adjustment for body mass index, physical activity, and other risk factors, the relative risks were 1.7 (95% CI: 1.3 to 2.3) for current smokers of > or = 20 cigarettes per day, 1.5 (95% CI: 1.0 to 2.2) for current smokers of <20 cigarettes per day, and 1.1 (95% CI: 1.0 to 1.4) for past smokers. Total pack-years of cigarette smoking was also associated with the risk of type 2 diabetes mellitus (P for trend <0.001).
Conclusions: These prospective data support the hypothesis that cigarette smoking is an independent and modifiable determinant of type 2 diabetes mellitus.