BackgroundA number of primary studies suggested that active smoking could be independently associated with incident diabetes. However less is known about the effect of active smoking and smoking cessation on glycemic control in patients with diabetes. The aim of this study was to evaluate the associations of active smoking and smoking cessation with glycemic control in diabetic patients. MethodsThe present was a cross-sectional study of 10551 men and 15297 women with diabetes from the Risk Evaluation of cAncers in Chinese diabeTic Individuals: a lONgitudinal (REACTION) study. Risk factors for glycemic control and the association of active smoking with glycemic control were evaluated using logistic regression models. Poor glycemic control was defined as HbA1c 7.0%. ResultsCurrent smokers have an increased risk of poor glycemic control, and the multivariable-adjusted odds ratio (OR) and 95% confidence intervals (CI) of HbA1c 7.0% with current smoking were 1.49 (1.35-1.66) in men and 1.56 (1.13-2.15) in women. Further analysis demonstrated a dose-dependent relationship between active smoking and the risk of poor glycemic control in men. Former smokers who quit smoking for <10years remained at increased risk of poor glycemic control, with the risk leveling off after 10years of smoking cessation compared with non-smokers, but risk in former smokers was significantly lower than that in current smokers. ConclusionsActive smoking is a modifiable risk factor for poor glycemic control in Chinese diabetic patients.