The Relationship between Smoking and Hemoglobin A1c in Adults without Diabetes Mellitus according to Body Mass Index

Background: Smoking is known to be closely related with cancer and cardiovascular diseases. Studies have shown that smoking increases hemoglobin A1c levels in patients with diabetes. We aimed to explore the relationship between smoking and hemoglobin A1c levels in adults without diabetes based on body mass index values. Methods: In a general hospital in Korea, we conducted a questionnaire-based survey among 406 adults (both men and women) with no history of diabetes. We collected information about their age, sex, smoking habits, drinking habits, exercise regime, height, weight, waist circumference, and blood pressure and conducted routine biochemical tests. Subjects were divided into groups according to their body mass index values, hemoglobin A1c levels, and smoking habits. Subsequently, the relationship between smoking and hemoglobin A1c levels was assessed. Results: We determined a correlation between smoking and hemoglobin A1c levels in all the subjects particularly those with normal body mass index values (body mass index below 23.0 kg/m 2 ). Subjects with a history of smoking were odds ratio [OR] 1.091 more likely (95% confidence interval [CI], 1.006–1.183; P=0.03) to have hemoglobin A1c levels between 5.7% to 6.4% as compared to those who were OR 1.168 (95% CI, 1.054–1.294; P=0.003) likely to have hemoglobin A1c levels below 5.6%. Conclusion: In all the subjects including adults with normal body mass index values (body mass index below 23.0 kg/m 2 ), a statistically significant relationship between smoking and hemoglobin A1c levels was observed.