Interaction of smoking and obesity on type 2 diabetes risk in a Chinese cohort

The aim of this study was to examine the independent and combined effects of current smoking and obesity on risk of type 2 diabetes (T2DM) in a Chinese cohort. We analyzed the data from a population-based prospective cohort of 3598 participants aged 35-74 years from Jiangsu, China. A Cox proportional hazards regression model was used to calculate the hazard ratio (HR) of T2DM and corresponding 95% confidence interval (CI), and to examine the interaction between current smoking and obesity on risk of T2DM. Compared with non-smokers, the hazard ratio of T2DM for current smokers was 4.16 (2.77-6.24). There was a significant interaction between current smoking and abdominal obesity on T2DM. RERI=2.84 (0.02-5.67), suggesting that there would be 2.84 relative excess risk due to the additive interaction; AP=0.48 (0.20-0.76), indicating that 48% of T2DM exposed to both risk factors was attributable to the additive interaction; and SI was 2.36 (1.15-4.87), suggesting that the risk of T2DM in obese smokers was 2.36 times as high as the sum of risks in the participants exposed to a single risk factor alone. We did not find a significant interaction between smoking and overall obesity on T2DM, but the incidence of T2DM in overall obese smokers was also highest. Both current smoking and abdominal obesity are strong risk factors of T2DM in the Chinese population. This study further demonstrates an additive interaction of current smoking and abdominal obesity on T2DM risk.