Association between menopausal age and smoking status defined using urinary cotinine or tobacco-specific nitrosamine metabolite 4-(methylnitrosamino)-1-(3-pyridyl)-1-butanol: The Korea National Health and Nutrition Examination Survey 2016–2018

This study aimed to establish the optimal cut-off values for urinary cotinine and 4-(methylnitrosamino)-1-(3-pyridyl)-1-butanol (NNAL)to determine smoking status in Korean women over 20 years of age and to assess the correlation of these biomarkers with reproductive health, particularly menopausal age, in postmenopausal women. Utilizing data from the 7th edition of the Korea National Health and Nutrition Examination Survey (2016–2018), researchers included postmenopausal women aged 40–60 years who were within 5 years of menopause. Self-reported smoking status was aligned with biomarkers levels to calculate optimal cut-off values, classifying a total of 503 postmenopausal women into four groups: never smokers (cotinine <0.738 ng/mL, NNAL <1.595 pg/mL), secondhand smokers (SHSrs; cotinine 0.738–37.7 ng/mL, NNAL 1.595–12.35 pg/mL), light current smokers (cotinine 37.7–837 ng/mL, NNAL 12.35–91.55 pg/mg), and heavy current smokers (cotinine >837 ng/mL, NNAL >91.55 pg/mL). Differences in menopausal age were analyzed using Kaplan–Meier curves and log-rank tests. The results indicated significant differences in menopausal age between never smokers and heavy smokers (51.4 ± 3.9 vs. 49.6 ± 3.0 years, p = 0.001) as well as SHSrs and heavy smokers (51.4 ± 3.3 vs. 49.6 ± 3.0 years, p = 0.001) when applying urinary cotinine cutoff values. However, no significant differences in menopausal age were observed based on NNAL cutoffs. These findings suggest urinary cotinine levels correlated more strongly with menopausal age than using urine NNAL levels for defining smoking status among postmenopausal Korean women. Heavy current smokers, as identified by urinary cotinine levels, experienced menopause at an earlier age compared to never smokers and SHSrs.