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.