Data from participants in the CoLaus study, Switzerland, aged 35–75 at baseline and followed for 5.5 years were used. Participants were classified as smokers, recent (≤ 5 years), long-term (> 5 years) quitters, and non-smokers at baseline. Outcomes were IFG (fasting serum glucose (FSG) 5.6–6.99 mmol/l) and T2DM (FSG ≥ 7.0 mmol/l and/or treatment) at follow up.
3,166 participants (63% women) had normal baseline FSG, of whom 26.7% were smokers, 6.5% recent quitters, and 23.5% long-term quitters. During follow-up 1,311 participants (41.4%) developed IFG (33.6% women, 54.7% men) and 47 (1.5%) developed T2DM (1.1% women, 2.1% men). Former smokers did not have statistically significant increased odds of IFG compared with smokers after adjustment for age, education, physical activity, hypercholesterolemia, hypertension and alcohol intake, with OR of 1.29 [95% confidence interval 0.94–1.76] for recent quitters and 1.03 [0.84–1.27] for long-term quitters. Former smokers did not have significant increased odds of T2DM compared with smokers with multivariable-adjusted OR of 1.53 [0.58–4.00] for recent quitters and 0.64 [0.27–1.48] for long-term quitters. Adjustment for body-mass index and waist circumference attenuated the association between recent quitting and IFG (OR 1.07 [0.78–1.48]) and T2DM (OR 1.28 [0.48–3.40].
In this middle-aged population, smoking cessation was not associated with an increased risk of IFG or T2DM.