Association between cigarette smoking and diabetes mellitus using two different smoking stratifications in 145 040 Korean individuals: Self-reported questionnaire and urine cotinine concentrations

Background: Although previous studies have assessed the relationship between smoking and diabetes using self-reported questionnaires, interpretations may be limited by an underestimation of the actual smoking population. This study evaluated the relationship between smoking and diabetes using both self-reported questionnaires and urine cotinine concentrations. Methods: The present cross-sectional study enrolled 145 040 Koreans in Kangbuk Samsung Health and Cohort Studies between 2011 and 2013. Urinary cotinine was measured after a 10-hour smoking-free period. Cotinine-verified current smoking was defined as a urinary cotinine concentrations ≥50 ng/mL. Results: Overall diabetes prevalence in self-reported (4.5% vs 1.6%) and cotinine-verified (4.4% vs 2.1%) current smokers was higher than in self-reported and cotinine-verified never smokers. Multivariate regression analysis showed that cotinine-verified current smoking (odds ratio [OR] 1.25; 95% confidence interval [CI] 1.13-1.38), self-reported former smoking (OR 1.16; 95% CI 1.01-1.33) and current smoking (OR 1.33; 95% CI 1.17-1.50) were associated with increased diabetes compared with cotinine-verified and self-reported never smoking. Unobserved smoking (OR 1.79; 95% CI 1.20, 2.66) also increased the odds for diabetes. There were no significant sex interactions in the analyses. Conclusions: This study shows that self-reported former and current smoking, cotinine-verified current smoking, and unobserved smoking (i.e. self-reported never smoking with urine cotinine >50 ng/mL) are all associated with increased diabetes prevalence. These findings suggest that cotinine could provide additional information when assessing cardiometabolic risks, such as diabetes.