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How Alcohol Affects Sleep

Updated: Mar 6

Alcohol and sports are often two peas in a pod. Beer is served throughout crowds, exists in many locker rooms of professional sports teams, is used to celebrate wins (and sulk in losses), can be ingrained in a sport and/or nation’s culture, and for some athletes, is used for relaxation after games.

 

Researchers have even studied beer as a potential post-training recovery fluid. You can read that here.

 

On the flip side, sleep is an easy tactic to promote an athlete’s recovery.

 

In this article, I’m going to review the following:

  • A brief intro of what alcohol is.

  • The sleep stages and cycle.

  • Alcohol’s impact on sleep.

  • Why an athlete should care.

  • A fun fact about alcohol metabolism (hint: the face flushing).

 

 

A Brief Primer on Alcohol

 

It forever surprises me how unaware athletes are of alcohol’s detrimental impact on their overall health. A few health-oriented takeaways:

 

  • Alcohol is a carcinogen for multiple gastrointestinal cancers, plus other peripheral systems and organs. (1)

  • It provides no metabolic benefits to the body. (2) Unlike calcium or protein, humans do not need alcohol.

  • Alcohol intake is correlated with a reduction in immune health for several hours post-consumption. (1, 3)

  • Heavy alcohol intake is correlated with low bone mineral density and increased risk of bone fracture. (4)

  • Most of the alcohol consumed is converted into body fat, and thus can contribute to weight gain and a change in the athlete’s speed and biomechanics (e.g., a baseball swing, ability to clear the bar in high or pole vault, abdominal fat restricting an oarsmen’s catch and finish positions). (1)

 

 

I also found The Alcohol Pharmacology Education Partnership modules, powered by Duke University, to be quite helpful.

 

 

What is Alcohol?

 

Whatever drink the alcohol is within, the alcohol molecule is the same and is referred to as ethanol. You can think of ethanol as a $5 bill: It doesn’t matter who's carrying it, it remains a $5 bill. Mojito? Organic wine? Champagne? Kendall Jenner’s tequila? The core ethanol remains the same.

 

The terminal hydroxyl group (the –OH) is polar, meaning it can interact with and dissolve in water. The 2-carbon chain (C—C) is non-polar and repels from water, allowing it to interact with fat. This polar—non-polar molecule allows it to act two-fold throughout the body. In order for someone to feel drunk, ethanol has to pass through the blood-brain barrier and into the brain. Ethanol can do this because of its non-polar C—C side. (5)

From a calorie perspective:

  • Carbohydrates and protein each provide 4 calories/gram (kcal/g).

  • Alcohol 7 kcal/g.

  • Fat 9 kcal/g.

 

 

How is Alcohol Metabolized?

 

Ethanol is metabolized primarily in the liver, but can be metabolized in the stomach and other tissues. (2) It first enters a liver cell where it is converted by the enzyme alcohol dehydrogenase (ADH) into the toxic acetaldehyde. From there, acetaldehyde travels into the mitochondria and is quickly converted into acetic acid by the enzyme aldehyde dehydrogenase (ALDH). (6)

If ethanol levels are high enough to overwhelm ADH, the microsomal ethanol oxidizing system (MEOS) can be used to metabolize ethanol with the enzyme CYP2E1. This occurs in the endoplasmic reticulum and accounts for 20% of ethanol metabolism. A third option is the catalase system, but this accounts for less than 2%. (2)

 

ADH7 also exists in the gastric mucosal cells and can metabolize upwards of 30% of the ethanol before it enters the blood. Females seem to have less ADH7 activity, meaning more ethanol can enter their system resulting in a higher blood alcohol level. (2)

 

Alcohol will absorb faster into circulation in the absence of food and/or liquid calories, but that’s not terribly safe, as blood alcohol levels will sharply increase. In the presence of food, alcohol absorption will be slowed, and is a safer way to consume alcohol as its side effects will have a delayed onset.

 

 

What are the Sleep Stages during a Sleep Cycle?

 

There are four sleep stages: Stages 1-3 are non-REM sleep (non-rapid eye movement) and stage 4 is REM. An electroencephalograph (EEG) monitors brain activity during sleep and lets researchers know what stage a sleeping person is in based on the waves appearing on the report. (7)


N1 – Stage 1 sleep (5-10% of total sleep time, or 1-5 minutes per cycle): This is the lightest stage of sleep where heart rate and breathing rate will begin to decrease. (8) If someone called your phone, woke you from N1, and you answered, you would be able to talk to them without them realizing you had been sleeping. (9,10) An EEG reading would show low-voltage theta waves. (8)

 

N2 – Stage 2 sleep (50%): Sleep becomes deeper and breathing and heart rate continue to decrease. (9,10) On an EEG, you would see sleep spindles (sawtooth pattern) and K complexes (long delta waves). Do you grind your teeth? This is the sleep stage when it occurs. (8)

 

N3 – Stage 3 sleep or slow wave sleep (18-25%): This is the deepest form of non-REM sleep. (3,8) An EEG report would show delta waves, which are low frequency and high amplitude. N3 is when sleepwalking, night terrors, and bedwetting occurs. (8)

 

REM (20-25%): Here’s where you dream and the body goes into paralysis (you wouldn’t want to act out your dreams). (3) The brain is laying down new pathways, memories, and is cementing what you learned that day. (9) Through the first sleep cycle, REM sleep lasts 10 minutes, whereas in the last cycle, REM extends to an hour. (8) Given this activity and progressively longer cycle, REM sleep increases the brain’s metabolism by nearly 22%. (11)

 

Overall, one sleep cycle lasts 90-110 minutes and includes all four stages in the following order: N1, N2, N3, N2, REM (which is why we spend so much time in N2). (8-10)

 

 

Does Alcohol Affect Sleep?

 

When reviewing this topic in the literature, the obvious group to study is alcoholics. Keep this in mind when searching for journal articles, as a paper on alcoholics isn’t the same as the soccer players you’re working with. Be mindful about how you read and apply your learnings.

 

Alcohol acts as a sedative/depressant and has been shown to decrease sleep onset latency, or the time it takes to fall asleep once your head hits the pillow. (3) It makes sense why someone with insomnia, someone who consumed too much caffeine in the day, and/or an athlete looking to relax and fall asleep may consume alcohol before bed.

 

However, even if that glass of red wine relaxes you and puts you to sleep, alcohol interferes with sleep quality. Colrain et al. (2014) reported that “REM sleep is suppressed, with a longer latency to REM sleep and decreased REM sleep in the first half of the night or across the whole night. In the second half of the night, sleep is disrupted, with increased wakefulness and/or stage 1 sleep.” (3) So, the ever-important REM sleep with cycle length increasing through the night will be negatively affected.

 

For papers evaluating the acute effects of alcohol, the impact on sleep was worse the closer the alcohol was consumed to falling asleep. Identical to eating, once consumed your body then needs to digest, absorb, and metabolize the meal. Your blood sugars will slowly increase, hit a peak, and then come back down—hours after finishing the meal. For alcohol, your blood alcohol levels will continue to rise after consumption—meaning that while you sleep, blood alcohol increases as ethanol gets in line to be metabolized.


I mentioned above the importance of eating when consuming alcohol as a safety measure. The flip side is that when alcohol and food are consumed together close to bedtime, blood alcohol levels will rise more slowly and therefore negatively impact your sleep for longer. This is not a recommendation to forego food to promote (eventually) better sleep. If you don’t want alcohol to affect your sleep quality, either consume it far away from bedtime or don’t consume it at all.

 

Another consideration is what happens when we have a terrible night’s sleep. Maybe you rely on caffeine more often the next day, are then more alert at night because of the caffeine still circulating in your body, and then, when you can’t get to sleep, you reach for a glass of wine. You fall asleep quickly, sleep quality is negatively affected, and the cycle happens all over again. There is a correlation between insomnia and alcoholism. (3)

 

And lastly, alcohol is a diuretic. If you drink before going to bed, you may be rustled out of sleep to pee, further impairing sleep quality and quantity. (9)

 

 

Why Does this Matter for Athletes?

 

Given alcohol’s high-calorie-per-gram content and how the body is likely to store it as fat mass, of which high levels aren’t considered a functional body tissue for athletic performance, there’s a body composition component. That seems obvious given the “beer belly” label evident in our culture.

 

What isn’t as obvious of a connection is the increased risk of injury rates with poor sleep—to which alcohol intake could be a contributor. It’s not uncommon for athletes to drink after a game and then either play or practice the next day.

 

A study in adolescent athletes in grades 7-12 (self-reported, online study) found that those averaging fewer than eight hours of sleep per night had an injury risk 1.7 times that compared to those sleeping ≥8 hours per night. (12)


For NCAA Division 1 male basketball players, Watson et al. (2020) collected daily data on 19 athletes over the course of two seasons. During that time, 32 injuries occurred, average sleep duration was 7.44±1.2 hours, and 83% of athletes slept fewer than eight hours per night. On the days when injuries occurred, self-reported athlete data indicated that mood, fatigue, stress, soreness, and sleep duration and quality were all ranked significantly lower compared with non-injury days. Injuries per 1,000 hours were highest for those athletes sleeping fewer than eight hours per night. Ultimately, the researchers reported that “a 1-hour increase in sleep duration was associated with a 43% decrease in injury risk the following day.” (13)



Take-Home Message: Don’t Use Alcohol as a Sleep Aide

 

The hard part about alcohol is how normalized it is in Western culture. Yes, athletes can understand that excessive alcohol the night before a game isn’t a good idea, but small doses before bedtime clearly matter. When educating teams about sleep, talk about alcohol and injury risk. And when educating on alcohol, go beyond body composition and talk about sleep and injury risk.

 

Thank you for reading until the end. Here’s a fact I found interesting: One isoenzyme variant of ALDH, ALDH2^2, “codes for a non-functional ALDH enzyme” and is inherited by half of Asians (I’ll refer to the ALDH2^2 as defective). Due to this, the flushing of the face, nausea, headache, and rapid heart rate are symptoms that occur when someone with ALDH2^2 consumes alcohol. Yet red cheeks aren’t a non-issue: It represents the inability to break down the toxic acetaldehyde. Given humans inherit two copies for each gene, their possible genotypes and reactions to consuming alcohol could be:

  • Effective-effective: Symptoms of mild-to-no flushing occurring in 50% of Asians.

  • Effective-defective: Flushing appears and occurs in 30-40% of Asians.

  • Defective-defective: Severe flushing occurring in 5-10% of Asians.


For those with a defective form, alcohol metabolism is slowed and blood alcohol levels remain elevated for longer. (14)

 


References


(1) Jeukendrup, A., & Gleeson, M. (2019). Sport nutrition 3/e. Human Kinetics.


(2) Gropper, S.S., Smith, J.L., & Carr, T.P. (2022). Advanced nutrition and human metabolism 8/e. Cengage.


(3) Colrain, I.M., Nicholas, C.L., & Baker, F.C. (2014). Alcohol and the sleeping brain. Hand Clin Neurol,125:415-431.


(4) Nelms, M., Sucher, K.P., Lacey, K., & Roth, S.L. (2011). Nutrition therapy & pathophysiology 2/e. Wadsworth Cengage Learning.


(5) The Alcohol Pharmacology Education Partnership. (n.d.). What is alcohol? https://sites.duke.edu/apep/module-1-gender-matters/content/content-what-is-alcohol/


(6) The Alcohol Pharmacology Education Partnership. (n.d.). Content: biological factors influence alcohol intoxication--a focus on metabolism. https://sites.duke.edu/apep/module-2-the-abcs-of-intoxication/content-biological-factors-influence-alcohol-intoxication-a-focus-on-metabolism/



(8) Patel, A.K., Reddy, V., Shumway, K.R., & Araujo, J.F. (2024, January 26). Physiology, sleep stages. https://www.ncbi.nlm.nih.gov/books/NBK526132/


(9) Mohr, C., & Mohr, K. (2020, October 29). Strategies for better sleep [Webinar]. Today's Dietitian, online.


(10) National Sleep Foundation. (2020, November 12). What are the sleep stages? https://www.thensf.org/what-are-the-sleep-stages/


(11) Peever, J., & Fuller, P.M. (2017). The biology of REM sleep. Curr Biol,27(22):R1237-R1248


(12) Milewski, M.D., Skaggs, D.L., Bishop, G.A., Pace, J.L., Ibrahim, D.A., ... & Barzdukas, A. (2014). Chronic lack of sleep is associated with increased sports injuries in adolescent athletes. J Pediatr Orthop,34(2):129-133.


(13) Watson, A., Johnson, M., & Sanfilippo, J. (2020). Decreased sleep is an independent predictor of in-season injury in male collegiate basketball players. Orthop J Sports Med,8(11):2325967120964481


(14) Wall, T.L., & Ehlers, C.L. (1995). Genetic influences affecting alcohol use among Asians. Alcohol Health Res World,19(3):184-189.



 

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