LAUSR

No study has reported the relationship between secondhand smoke (SHS) exposure and metabolic syndrome (MetS) in self-reported never-smokers verified by nicotine metabolite. The aim of this study is to determine the relationship between SHS exposure and MetS in self-reported and cotinine-verified never-smokers. A total of 118,609 self-reported and cotinine-verified never-smokers (38,385 men; age 34.8±7.1 years) who participated in Kangbuk Samsung Health Study (KSHS) and Kangbuk Samsung Cohort study (KSCS) between 2011 and 2016 were included. Cotinine-verified never-smoker was defined as individuals having urinary cotinine <50 ng/mL. SHS exposure was defined as having experienced passive smoking indoors at home or the workplace. The prevalence of SHS exposure in the overall population was 22.6%, with rates of 27.4% for males and 20.3% for females (p<0.001). The overall prevalence of MetS was 6.8%; the prevalence in males was higher than that in females (10.7% versus 4.9%, p<0.001). In both males and females, the prevalence of MetS in group with SHS exposure was higher than that in group without SHS exposure (11.3% versus 10.4%, p=0.010 for males; 5.8% versus 4.6%, p<0.001 for females). However, there was significant gender interaction for the relationships between SHS exposure and MetS (p for interaction=0.010). A multivariate regression model was adjusted for the baseline variables including age, body mass index, frequency of alcohol drinking and vigorous exercise, blood urea nitrogen, creatinine, uric acid, total cholesterol, LDL cholesterol, and hsCRP. The results showed that SHS exposure only in females was associated with MetS (odds ratio [95% confidence interval], 1.17 [1.06, 1.29] for females; 1.02 [0.94, 1.11] for males). In particular, females with SHS exposure of ≥1 hours/day, ≥3 times/week, and ≥10 years increased the prevalence of MetS compared to those without SHS exposure (1.21 [1.02, 1.45], 1.30 [1.14, 1.49], and 1.12 [0.99, 1.28], respectively. This study showed that the SHS exposure in females was significantly associated with MetS in self-reported never-smokers with low urinary cotinine levels (<50 ng/mL), suggesting that more active anti-smoking programs in the home and public are needed to reduce the risk of MetS.