Effect of smoking on hemoglobin A_1c and body mass index in patients with type 2 diabetes mellitus

Background: Smoking is associated with a decrease in body weight in patients without diabetes mellitus and an increase in insulin resistance and hemoglobin A_1c (HbA_1c) levels in patients with type 1 diabetes mellitus. Whether smoking is associated with an increase in HbA_1c and/or a decrease in body mass index (BMI) in type 2 diabetes mellitus is unresolved, however. Therefore, the objective of this study was to determine the effect of smoking on HbA_1c levels and BMI in a cross-section of outpatients with type 2 diabetes mellitus. Methods: A questionnaire was completed by 102 sequential outpatients (32 men, 70 women) with type 2 diabetes mellitus to assess age, sex, duration of diabetes mellitus, medications, exposure to nicotine, medical complications as a result of type 2 diabetes mellitus, and BMI. In addition, a urine sample was obtained from each patient to assess the microalbumin-creatinine and cotinine-creatinine ratios. HbA_1c level were also obtained from each volunteer as a measure of glucose control. Results: Smokers had significantly higher cotinine-creatinine ratios than nonsmokers. Smokers and nonsmokers did not differ significantly with regard to HbA_1c level, BMI, or duration of diabetes mellitus. Smokers were younger than nonsmokers. Smokers and nonsmokers did not differ significantly in terms of microalbumin-creatinine ratio, amount of diabetic medications, or medical complications. Conclusion: The results of this study suggest that smoking does not have a significant direct effect on BMI or HbA_1c in patients with type 2 diabetes mellitus. This conclusion suggests that the relationship between these factors is much more complex than in people without diabetes or in patients with type 1 diabetes mellitus.