Cigarette Smoking Linked to Poor Glycemic Control in T1DM

Smoking and T1DM. Previous studies have not used longitudinal measurements of both glycemic control and smoking history in a large cohort of patients with T1DM. Authors of this study sought to assess the immediate and long-term association between smoking, glycemic control, and T1DM-related complications. They also evaluated the extent to which glycemic control alters the association between smoking and those complications. 

The Study. Utilizing data from the Diabetes Control and Complications Trial, authors assessed whether intensive diabetes treatment would prevent development and/or progression of T1DM-related complications. Authors randomized 1441 T1DM patients, mean age 27 years, to receive either intensive therapy or conventional therapy. Patients were evaluated quarterly with examinations and assessments of glycemic control (A1c values). Retinopathy and nephropathy were assessed and data was collected on smoking behaviors with patients being placed into 3 different smoking categories. 

The Results. 20% of patients were current smokers and 15% were former smokers. Mean A1c levels differed by smoking status with the highest among current smokers. Mean A1c levels were higher for ever smokers vs never smokers (0.16%, P<.01) and the risk of microvascular complications were higher in current vs never smokers. The increased risk of retinopathy and nephropathy among current smokers was not statistically significant after including A1c as a time-dependent covariate in Cox proportional hazards regression models.

Take Home Points. Patients with T1DM who smoke are at a higher risk for poor glycemic control and microvascular complications. After adjusting for A1c, the relationship between smoking and complications was attenuated, pointing to poor glycemic control associated with smoking as the primary factor. Physicians should encourage smoking cessation in all patients and counsel T1DM patients that glycemic control may be improved by doing so.