Cigarette smoking and glycaemia: The EPIC-Norfolk study

Abstract

Background: Previous prospective studies have suggested that cigarette smoking may be associated with an increased risk of type 2 diabetes, but the possibility of confounding, particularly by dietary factors has not been fully examined. Methods: Cross-sectional analysis of the association between cigarette smoking and HbA1C, a marker of long-term glucose homeostasis in 2704 men and 3385 women, aged 45-74 years who were recruited to a population-based study of diet and chronic disease. Results: Twelve per cent of men and 11% of women reported being current smokers. Mean HbA1C was lowest in never smokers, intermediate in former smokers and highest in current smokers. There was a dose-response relationship between HbA1C levels and number of cigarettes smoked per day and a positive association with total smoking exposure as measured by pack-years. The unadjusted increase in HbA1C for 20 pack-years of smoking was 0.12% (95% CI: 0.09-0.16) in men and 0.12% (95% CI: 0.08-0.17) in women. After adjustment for possible confounders including dietary variables, the values were 0.08% (95% CI: 0.04-0.12) and 0.07% (95% CI: 0.02-0.12) for men and women, respectively. Mean HbA1C was inversely related to time since quitting smoking in men. Conclusions: These results add support to the hypothesis that smoking has long-term effects on glucose homeostasis, an association that cannot be explained by confounding by dietary factors as measured in this study.