© 2015 Elsevier Ltd. Background: Smoking increases the risk of developing type 2 diabetes. However, several population studies also show a higher risk in people 3-5 years after smoking cessation than in continuing smokers. After 10-12 years the risk equates to that of never-smokers. Small cohort studies suggest diabetes control deteriorates temporarily during the first year after quitting. We examined whether or not quitting smoking was associated with altered diabetes control in a population study, for how long this association persisted, and whether or not this association was mediated by weight change. Methods: We did a retrospective cohort study (Jan 1, 2005, to Dec 31, 2010) of adult smokers with type 2 diabetes using The Health Improvement Network (THIN), a large UK primary care database. We developed adjusted multilevel regression models to investigate the association between a quit event, smoking abstinence duration, change in HbA 1c , and the mediating effect of weight change. Findings: 10 692 adult smokers with type 2 diabetes were included. 3131 (29%) quit smoking and remained abstinent for at least 1 year. After adjustment for potential confounders, HbA 1c increased by 0·21% (95% CI 0·17-0·25; p < 0·001; [2·34 mmol/mol (95% CI 1·91-2·77)]) within the first year after quitting. HbA 1c decreased as abstinence continued and became comparable to that of continual smokers after 3 years. This increase in HbA 1c was not mediated by weight change. Interpretation: In type 2 diabetes, smoking cessation is associated with deterioration in glycaemic control that lasts for 3 years and is unrelated to weight gain. At a population level, this temporary rise could increase microvascular complications. Funding: National Institute for Health Research School for Primary Care Research.

Original publication




Journal article


The Lancet Diabetes and Endocrinology

Publication Date





423 - 430