Objectives: We investigated the association between smoking and its additive effects with insulin resistance and beta-cell function on the incidence of type 2 diabetes in a prospective population-based cohort study.
Design and method: A total of 10 038 subjects were recruited from rural and urban areas. All subjects underwent 75 g oral glucose tolerance tests and full biochemical assessments at baseline and during 4-year follow-up period. The final analysis was limited to 4041 men due to the low smoking rates in women.
Results: The ex- and heavy current smokers had the highest incidence of diabetes of 12.5% and 11.1% respectively, compared with never-smokers (7.9%) during 4 years. After multivariate adjustment by Cox-proportional hazard model, ex- and current smokers reveal a relative risk of 1.60 (95% CI: 1.07-2.39), 2.06 (1.35-3.16, for <20 cigarettes/day) and 2.41 (1.48-3.93, for > or =20 cigarettes/day) respectively compared with never smokers. The risk of new onset diabetes was the highest in those with low homeostasis model assessment for beta cell function (HOMA-beta) and high homeostasis model assessment for insulin resistance (HOMA-IR) group in both smokers and never smokers.
Conclusions: Smoking is an independent risk factor for type 2 diabetes mellitus and showed synergistic interaction with the status of low insulin secretion and high insulin resistance for developing diabetes. Given the high rates of smoking and growing burden of diabetes in the world, cessation of smoking should be considered as one of the key factors for diabetes prevention and treatment programmes.