The Association between Smoking Cessation and HbA1c Control of Diabetes Mellitus: A THIN database study

Itroduction Preliminary evidence suggests control of diabetes deteriorates initially after stopping smoking. Our objective was to examine whether smoking cessation was associated with deterioration in diabetes control. Methods A retrospective cohort study (01/01/05-31/12/10) was conducted using The Health Improvement Network (THIN) database, which is representative of the UK population. Inclusion criteria were: patients aged over 18, registered with their practice for at least one year on 01/01/05, diagnosed with type 2 diabetes mellitus (T2DM) and whose last recorded smoking status before 2005 was current smoker. An adjusted multilevel regression model was developed to investigate the association between change in HbA1c and stopping smoking. Results 10,692 adults with T2DM were current smokers at 1st January 2005. Of these, 3,131 (29%) quit smoking and remained abstinent for one year or longer. After adjustment for potential confounders, patients who quit smoking had a mean post-quit increase in HbA1c of 2.3mmol/l (95% CI 1.91 to 2.77, p<0.001) that persisted for three years. The deterioration was not mediated by weight gain. Discussion Smoking cessation is associated with deterioration in glycaemic control in people with type 2 diabetes that persists for three years and appears not to be caused by weight gain. The rise in HbA1c is minor for each patient and clinician but will substantially increase microvascular complications in the whole population, which could be prevented by prompt action to improve glycaemic control on cessation.