Concentrations of cotinine and 4-(methylnitrosamino)-1-(3-pyridyl)-1-butanol (NNAL) in US non-daily cigarette smokers.

Background: Accumulating evidence suggests that non-daily smokers have higher disease and mortality risks than never smokers. Yet, the accuracy of self-reported non-daily cigarette smoking is poorly understood. Methods: We examined the concordance between self-reported non-daily smoking and serum cotinine in 18,835 adult participants (20 years or older) of the 2007-2014 National Health and Nutrition Examination Surveys, in comparison with daily smokers and non-smokers. We also analyzed concentrations of the urinary biomarker 4-(methylnitrosamino)-1-(3-pyridyl)-1-butanol (NNAL) by smoking status. Results: In the study sample, 77.8% (14,660) reported currently not smoking (non-smokers), 18.3% (3,446) smoked every day (daily smokers) and 3.9% (729) smoked on some days of the past month (non-daily smokers). Just 2.1% of non-smokers had cotinine concentrations in the active smoking range (>10 ng/mL), compared to 70.4% of non-daily and 98.8% of daily smokers. Non-daily smokers reported smoking a median of 24 cigarettes per month (interquartile range (IQR): 9-60) and had substantially higher concentrations of NNAL (Median: 72.5, IQR: 14.8-211.0 pg/mL) than non-smokers (Median: 0.4, IQR: 0.4-2.1 pg/mL), though lower than daily smokers (Median: 294.0, IQR: 148.0-542.0 pg/mL). Among non-daily smokers, concentrations of cotinine and NNAL were positively correlated with days and cigarettes smoked per month (P<0.001). Conclusions: We observed excellent concordance between self-reported non-daily cigarette smoking and concentrations of serum cotinine. Impact: These results provide evidence for the validity of self-reported non-daily smoking and indicate that non-daily smokers are exposed to substantial concentrations of carcinogenic nitrosamines regardless of the low number of cigarettes they smoke per month.