Nicotine is both a stimulant and a depressant and while it may seem relaxing, it can actually increase heart rate and wakefulness. Nicotine is also heavily addictive and withdrawal may occur during the night, potentially disrupting sleep.
Why this could improve your sleep?
Reducing or eliminating nicotine can improve your sleep by reducing the amount of time it takes to fall asleep and possibly the number of sleep disturbances. Avoiding nicotine can also help prevent the worsening of some respiratory and sleep disorders such as restless legs syndrome (RLS), obstructive sleep apnea (OSA), and chronic obstructive pulmonary disease (COPD).
Jaehne, A., Loessl, B., Bárkai, Z., Riemann, D., Hornyak, M. (2009). Effects of nicotine on sleep during consumption, withdrawal and replacement
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ASA Editor. (2016). Smoking and Sleep. Retrieved from https://www.sleepassociation.org/blog-post/smoking-and-sleep/
What to do about restless legs syndrome. (2012). Retrieved fromhttps://www.health.harvard.edu/diseases-and-conditions/what-to-do-about-restless-legs-syndrome