Effects of nicotine on sleep during consumption, withdrawal and replacement therapy.

Smoking constitutes the most important behavioural health risk in the Western world. By acting on various neurotransmitter systems, nicotine consumption also influences sleep and mood. Studies on the relationship between smoking, sleep disturbances, sleep-related disorders and depression led to dissimilar results. The aim of the present work is to provide a descriptive overview of the existing data regarding the relationship of nicotine consumption, withdrawal, replacement therapy and sleep disturbances in both animals and humans. Primarily symptoms of insomnia, such as increased sleep latency, sleep fragmentation and decreased slow wave sleep with reduced sleep efficiency and increased daytime sleepiness, were observed during nicotine consumption. Furthermore, most studies indicated a nicotine induced rapid eye movement (REM) sleep suppression. The effects on sleep due to therapeutic nicotine substitution after smoking cessation were often masked by withdrawal symptoms. Depressive non-smokers experienced a mood improvement under nicotine administration comparable to the effect of anti-depressants. In turn, depressive symptoms and sleep impairment during nicotine withdrawal had a negative impact on abstinence rates. Smoking was also associated with an increased prevalence of sleep-related respiratory disorders, which further worsened sleep quality and daytime sleepiness. The partly inconsistent findings of the analysed 52 studies result mostly from different methodology, necessitating a more unified approach with regard to subjects' assessment of smoking status, control for co-morbidity and use of medication as well as outcome criteria.