The association between cotinine-measured smoking intensity and sleep quality

INTRODUCTION Cigarette smoking is suggested to be associated with sleep problems. This study evaluated the quantitative association between urinary cotinine-verified smoking intensity and sleep quality assessed by the Pittsburgh Sleep Quality Index (PSQI).METHODS This was a cross-sectional study of 189970 participants from the Kangbuk Samsung Health Study recruited between 2016 and 2018. Logistic regression analysis adjusted for covariates was performed to estimate the association between urinary cotinine levels assessed by quartiles and poor sleep quality, defined as global PSQI score >5.RESULTS The odds ratios (OR) and 95% confidence intervals (CI) for poor sleep quality comparing the highest urinary cotinine quartile to non-smokers were: 1.23 (95% CI: 1.16-1.30) for overall, 1.19 (95% CI: 1.12-1.26) for males, and 1.55 (95% CI: 1.29-1.87) for females. Among self-reported never smokers, cotinine-verified smokers had higher odds for decreased sleep quality compared to cotinine-verified never smokers with OR of 1.26 (95% CI: 1.08-1.46).CONCLUSIONS Elevated urinary cotinine levels were associated with poor sleep quality in relatively young and middle-aged South Korean adults. Higher odds for poor sleep quality among cotinine-verified smokers who self-reported as never smokers also demonstrate the value of quantitative measurement of urinary cotinine. Prospective studies are warranted to clarify the cause-effect relationship between smoking and sleep quality.