Severity of nicotine addiction and disruptions in sleep mediated by early awakenings

Introduction: Sleep disruption is common among smokers, however, extant studies primarily explore differences between smokers and nonsmokers. The time to smokers' first cigarette of the day (TTFC) after waking, a strong indicator of addiction severity, is inversely associated with numerous health outcomes. The present study tests the hypotheses that, in a representative sample of daily smokers, the severity of nicotine addiction is associated with shorter habitual sleep duration and excessive daytime sleepiness. Methods: We examined the associations between TTFC and sleep outcomes (sleep duration and daytime excessive sleepiness) and the mediating effects of specific sleep disruption pathways (delayed sleep onset, awakenings at night, and early awakening) using structural equation modeling. Analyses included cross-sectional data from 2015 current daily smokers aged 16-85 years who participated in the 2005-2006 and 2007-2008 National Health and Nutrition Examination Survey. Results: Among daily smokers, earlier TTFC was associated with both shorter sleep duration and excessive daytime sleepiness (p values < .001, R² values = .15 and .29, respectively). Of sleep disruption pathways, only early awakening mediated the associations of TTFC with both outcomes (sleep duration: b = .02, 95% confidence interval [CI]: 0.006 to 0.042; daytime sleepiness: b = -.01, 95% CI: -0.03 to -0.004), even after controlling for variables confounded with smoking status and sleep outcomes. Conclusions: Findings suggest that early awakening may be the mechanism responsible for the association between nicotine addiction severity and poor sleep outcomes of shorter sleep duration and excessive daytime sleepiness. These data may inform cessation strategies, risk assessment, and future longitudinal studies on the relations between sleep and nicotine addiction. Implications: Smokers have impaired sleep quality and quantity as compared to nonsmokers; however, that severity of nicotine addiction is an important factor in sleep quality, not just smoking status. Higher levels of addiction lead to less sleep and more daytime sleepiness. The relation between addiction severity and sleep is mediated by waking too early in the morning, and not by difficulty falling asleep or waking during the night. These findings could play an important role in supplementing cessation efforts; sleep disruption may interact with other negative physiological and emotional symptoms related to nicotine withdrawal and could result in more cessation failure.