Alcohol is generally known to be a depressant (or numbing) substance, and “nightcaps” have been used for generations to help ease people to sleep. However, many research studies contradict this common belief and have found that in actuality, alcohol consumption disrupts sleep cycles and patterns, especially among habitual/binge drinkers and alcoholics.
A Patrick, Griffin, Huntley, and Maggs (2016) study found that college students reported worsened sleep quality and quantity following a night of binge drinking (defined as four or more drinks consumed by women and five or more drinks consumed by men in a single night). While this disrupted sleep could have been impacted by factors other than the consumption of alcohol, like the fact that these students may have stayed out late socializing, there are other studies to support the assertion that alcohol directly alters sleep patterns and is not simply a correlational observation.
A study by Roehrs and Roth (2001) uncovered a possible explanation for the “nightcap” misconception. According to their study, alcohol consumption in non-alcoholics improved sleep to an extent. Non-alcoholics that consumed lower levels of alcohol (meaning less than four or five drinks per night) experienced longer and higher quality sleep, but when they consumed larger amounts of alcohol (i.e. binge drinking), their sleep was worsened during the second half of the night. Roehrs and Roth (2001) also observed the impact of alcohol on the sleep of alcoholics, which process alcohol differently than non-alcoholics. As alcohol consumption becomes more habitual and consumers develop physical dependencies on the substance, the disruption of sleep becomes more chronic and persistent, and sleep disorders like apnea can develop. Apnea prevents sufferers from attaining restful sleep, or even much sleep at all, due to their inability to take in oxygen when unconscious. Similar to the trend in heavy drinkers and alcoholics, Ogeil et al. (2019) found that persistent heavy use of alcohol over time was correlated with poorer sleep quality among adolescents.
Based on these studies, and experiments performed by Chan, Trinder, Colrain, and Nicholas (2015), alcohol was determined to have an arousal effect on sleep waves and patterns, which competes with and inhibits delta activity which occurs during deep non-REM sleep (Carlson, 2013). The Chan et al. (2015) study found that alcohol increased frontal alpha activity, which competed with the delta activity to impede restful sleep. Though it is not clear exactly why alcohol reacts to disrupt sleep waves in this way, the arousing results are evidence that alcohol consumption, particularly in larger quantities, hinder sleep.
Additionally, the Chan et al. (2015) study provide a possible explanation for the sleep trends in adolescent drinkers and alcoholics because it demonstrated that alcohol actively prevents non-REM deep sleep, which results in less restful sleep. It is important that heavy nighttime drinking, which occur frequently on college campuses, is discouraged on the basis that habitual heavy drinking before bed can severely impede getting a restful night’s sleep due to the prevention of delta activity. Many studies have shown the negative impacts of sleep deprivation over time in general, and given the disruption alcohol consumption has on deep, restful non- REM sleep it is important to avoid large amounts of alcohol before bed as an essential aspect of healthy sleep hygiene.
Carlson, N. (2013). Foundations of behavioral neuroscience, ninth edition. New York: Allyn and Bacon.
Chan, J. K., Trinder, J. , Colrain, I. M. and Nicholas, C. L. (2015), The acute effects of alcohol on sleep electroencephalogram power spectra in late Adolescence. Alcoholism Clinical and Experimental Research, 39, 291-299. doi:10.1111/acer.12621
Ogeil, R. P., Cheetham, A., Mooney, A., Allen, N. B., Schwartz, O., Byrne, M. L., . . . Lubman, D. I. (2019). Early adolescent drinking and cannabis use predicts later sleep-quality problems. Psychology of Addictive Behaviors, 33(3), 266-273. http://dx.doi.org/10.1037/adb0000453
Patrick, M. E., Griffin, J., Huntley, E. D., & Maggs, J. L. (2018) Energy drinks and binge drinking predict college students’ sleep quantity, quality, and tiredness, behavioral sleep medicine, Behavioral Sleep Medicine, 16(1), 92-105, DOI: 10.1080/15402002.2016.1173554
Roehrs, T. & Roth, T. (2001). Sleep, sleepiness, sleep disorders and alcohol use and abuse. Sleep Medicine Reviews, 5(4), 287-297. https://doi.org/10.1053/smrv.2001.0162