Association of self-reported and cotinine-verified smoking status with incidence of metabolic syndrome in 47 379 Korean adults

Background: The relationship of cotinine-verified vs self-reported smoking status with the incidence of metabolic syndrome (MetS) is not known. This study investigated the effect of urinary cotinine-verified vs self-reported smoking status on incident MetS. Methods: In all, 47 379 participants without MetS enrolled in the Kangbuk Samsung Health Study and Kangbuk Samsung Cohort Study between 2011 and 2012 (baseline) were included in this study and followed-up in 2014; median follow-up duration was 25 months. Cotinine-verified current smoking was defined as urinary cotinine concentrations >50 ng/mL. According to cotinine-verified smoking status at baseline and follow-up, individuals were divided into four groups: never, new, former, and sustained smokers. Results: The incidence of MetS in the never, former, new, and sustained smoking groups was 9.9%, 19.4%, 21.4%, and 18.7%, respectively. Multivariate Cox hazard regression analyses revealed that the relative risk (RR) for incident MetS in cotinine-verified former smokers was significantly increased compared with that in cotinine-verified never smokers (RR 1.27; 95% confidence interval [CI] 1.16-1.37), especially in individuals exhibiting weight gain (≥2 kg). These results were consistent with those of self-reported smoking status. Baseline cotinine-verified current smoking (RR 1.09; 95% CI 1.03-1.15) and self-reported former (RR 1.10; 95% CI 1.02-1.18) and current (RR 1.15; 95% CI 1.07-1.23) smoking were also significantly associated with incident MetS. Conclusions: This large observational study showed that cotinine-verified and self-reported former smoking during follow-up increased the risk for incident MetS, especially in individuals exhibiting weight gain (≥2 kg). This suggests that weight control in former smokers would be very important to reduce the development of MetS.