Association between Cigarette Smoking and New-Onset Diabetes Mellitus in 78,212 Koreans Using Self-Reported Questionnaire and Urine Cotinine

Background: No study has assessed association between cigarette smoking and new-onset diabetes mellitus (NODM) incidence using two different smoking classification systems: self-reported questionnaire and urine cotinine. The objective of this longitudinal study was to evaluate NODM risk using the above two systems in Korean adults. Methods: Among individuals enrolled in Kangbuk Samsung Health Study and Cohort Study who visited between 2011 and 2012 at baseline and 2014 at follow-up, 78,212 participants without baseline diabetes mellitus were followed up for a median of 27 months. Assessment of NODM incidence was made at the end of follow-up period. Cotinine-verified current smoking was having urinary cotinine >= 50 ng/mL. Results: Percentages of self-reported and cotinine-verified current smokers were 25.9% and 23.5%, respectively. Overall incidence of NODM was 1.5%. According to multivariate regression analyses, baseline self-reported current smoking (relative risk [RR], 1.33; 95% confidence interval [CI], 1.07 to 1.65) and cotinine-verified current smoking (RR, 1.27; 95% CI, 1.08 to 1.49) increased NODM risk compared to baseline self-reported never smoking and cotinine-verified current non-smoking. Higher daily amount and longer duration of smoking were also associated with increased NODM risk (P for trends < 0.05). In particular, self-reported current smokers who smoked >= 20 cigarettes/day (RR, 1.62; 95% CI, 1.25 to 2.15) and >= 10 years (RR, 1.34; 95% CI, 1.08 to 1.67) had the highest RRs for NODM. These results remained significant in males, although there was no gender interaction. Conclusion: This longitudinal study showed that baseline self-reported and cotinine-verified current smoking were associated with increased risks of NODM, especially in males.