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 HbA_1C, 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 HbA_1C was lowest in never smokers, intermediate in former smokers and highest in current smokers. There was a dose-response relationship between HbA_1C 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 HbA_1C 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 HbA_1C 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.

KEY MESSAGES

• Previous studies have suggested that smoking may be associated with an increased risk of type 2 diabetes.

• In this cross-sectional study, mean HbA_1C, a marker of long-term hyperglycaemia was increased in current smokers.

• HbA_1C rose by 0.12% for each 20 pack-years of smoking.

• Adjustment for confounding reduced but did not eliminate this association.

• These data add support to the hypothesis that smoking has long-term effects on glucose homeostasis.

Smoking, glycosylated haemoglobin, diabetes mellitus, epidemiology