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Greetings!Welcome to the Physiology Friday newsletter.ICYMIOn Monday, I posted a video interview that I recorded with Aidan Chariton from Shortcut U. We discuss the importance of endurance training and other things related to human health and performance.On Wednesday, I posted my “7 Rules for Health.”Details about the sponsors of this newsletter including Examine.com and my book “VO2 Max Essentials” can be found at the end of the post!Physiologically Speaking is a reader-supported publication. To receive new posts and support my work, consider becoming a free or paid subscriber."Drink, sir, is a great provoker of three things… nose-painting, sleep, and urine. Lechery, sir, it provokes, and unprovokes; it provokes the desire, but it takes away the performance." – 'Macbeth' (1606) act 2, scene. 3, l. [28]It’s clear that Shakespeare recognized alcohol’s role as an intoxicant, a somnogen, and a diuretic.Though alcohol may be a “provoker” of good spirits and whimsy for a short while, its “unprovoking” effects on sleep are well known to most.I’m not a teetotaler, but I recognize the harmful effects of alcohol abuse. Some people enjoy a few drinks on occasional while others wish to abstain. I support both decisions.One often-cited reason for alcohol consumption is as a sleep aid — nearly 20% of adults in the United States say that they use alcohol for this purpose.There’s one problem with this strategy. Although alcohol may help you fall asleep (it’s a depressant after all), it impairs your ability to stay asleep and worsens the quality of your sleep.I’ve written on this subject before. Alcohol can elevate body temperature and heart rate, reduce heart-rate variability (HRV), and disrupt the regulation of our autonomic nervous system during sleep, all of which reduce the restorative quality of sleep.In higher quantities, alcohol disrupts the normal architecture of our sleep — architecture referring to the time we spend in the various sleep stages (i.e., light sleep, rapid eye movement or REM, slow-wave sleep/deep sleep). Alcohol also appears to cause more fragmented sleep, characterized by more wakefulness throughout the night. This may be due to the alcohol-induced increase in body temperature, an increased need to urinate owing to alcohol’s diuretic effect, apneic episodes during sleep (when we stop breathing), and the so-called “rebound effect” that occurs when alcohol is metabolized, which leads to wakefulness due to blood glucose fluctuations, dehydration, and digestive discomfort.All of these effects are well known to occur when alcohol is consumed in close proximity (e.g., 3 hours or less) to sleep and happen in a dose-dependent fashion. The more you drink and the closer to bedtime you drink, the more you disrupt your sleep.What is less well-understood is how (or if) alcohol’s effects on sleep persist, worsen, or diminish over consecutive nights of alcohol consumption. Does our brain and body “habituate” to repeated drinking episodes or is it a downward spiral until we abstain?It’s also not known if the effects of alcohol on sleep architecture are consistent throughout the night. In other words, does alcohol affect sleep stages differently a few hours after bedtime compared to in the middle of your sleep period?These questions were investigated in a new study published in the aptly named journal Sleep.A total of 30 participants completed the study (15 men and 15 women with an average age of 33), none of whom had Alcohol Use Disorder but all of whom reported a moderate drinking habit (9–12 standard drinks per week for women and 12–15 standard drinks per week for men). An important consideration given that people who don’t drink or who drink “too much” might have different responses to alcohol consumption.The participants completed two 3-night experimental conditions in a random order. A washout period of 4 nights separated each condition.In one condition, the participants consumed 3 standard drinks (targeting a breath alcohol concentration of 0.08) in 45 minutes. The last drink was about 1 hour before bedtime. If you're curious, the two choices were Everclear or vodka in some type of mixer. They did this for 3 nights in a row.In the other condition, the participants drank just a mixer (no alcohol; this was the control condition) before bed. As in the alcohol condition, they did this for 3 nights in a row.The participants also completed a standardization phase before the study. For 8 days, they maintained a regular sleep schedule at home (7.5–8.5 hours of sleep per night) and avoided recreational drugs and alcohol, sleep medications, and excessive caffeine (more than 360 mg per day or caffeine after 2 p.m.).Overnight, brain activity and other physiological metrics were measured using a technique known as polysomnography (PSG). PSG allows for, among other things, the measurement of the time spent in various sleep stages, which for this study included slow-wave sleep (SWS) and rapid-eye-movement sleep (REM). Other outcomes included the total sleep time or sleep duration, the time spent awake each night, sleep latency (the time it takes to fall asleep), and wake after sleep onset (WASO; how much time you spend awake after falling asleep for the first time).What made this study unique was the separation of each night into thirds, permitting a detailed insight into the specific “windows” of sleep that were most affected by alcohol. This produced some interesting findings that I’ll expand on in the next section.ResultsAs I discuss the results, keep in mind that in all cases, the specific nights or time points in the alcohol condition were compared to the average of all 3 nights or time points in the control condition.On all 3 nights with alcohol, SWS increased during the first third of the night compared to the control condition but was lower during the second two-thirds of the night compared to the control condition. On the other hand, REM sleep decreased on all 3 nights with alcohol compared to the control condition and also during the first third of the night (but not the second two-thirds).Using a unique temporal analysis, the researchers identified many differences in the timeframes when the amount of time in the various sleep stages was different between the conditions.The proportion of time spent in SWS was higher in the alcohol condition (vs. the control condition) between 1.8 and 6.5 hours after bedtime. This was consistent across all 3 nights, and indicates that the effects of alcohol on SWS are persistent.The proportion of time spent in REM sleep was lower in the alcohol condition on night 1, specifically between 1.4 and 7.8 hours after sleep onset. On nights 2 and 3, REM sleep was lower between 2.1 and 5.3 hours after sleep onset. Put another way, the effects of alcohol on REM sleep diminished (occurred in a narrower time frame) with consecutive nights of alcohol consumption.WASO was only higher on night 1 of alcohol consumption compared to the control condition, specifically from 5.6 hours after sleep onset until wake time.There were also some notable differences between nights 1, 2, and 3 of alcohol consumption.For one, the participants spent more time awake on alcohol night 1 vs. alcohol night 2 (from 1 to 2.7 hours after sleep onset) and on alcohol night 2 vs. night 3 (from 5.1 to 6.7 hours after sleep onset). Second, WASO was different on alcohol night 1 vs. night 2 (from 5.2 hours after sleep onset until awake) and on night 1 vs. night 3 (from 5.4 hours after sleep onset until awake).These results indicate a few things about the impact of consecutive nights of alcohol consumption on sleep:Pre-sleep alcohol reduces SWS, effects that begin around 2 hours after going to sleep or right around the end of the first sleep cycle. These effects persist when alcohol is consumed for three nights in a row.Consecutive nights of pre-sleep alcohol consumption decreases REM sleep, but these effects seem to be worse on the first night (an 11-minute decrease in total REM sleep) compared to the second and third nights (a 4-minute decrease in total REM sleep).Alcohol seems to increase wakefulness in the later periods of sleep, from about 5 hours after sleep onset until the time you wake up.The findings on REM sleep may indicate that the nervous system somehow adapts to these pre-sleep alcohol levels to “rescue” time spent in REM sleep, but this doesn’t happen for SWS.REM sleep is where dreams occur. During REM, our brain activity, breathing, and heart rate and blood pressure increase. Our eyes also move back and forth rapidly, hence the name. REM sleep is thought to play an important role in memory and learning and likely had an important evolutionary role.This doesn’t mean SWS is any less important. SWS, also known as deep sleep, happens early in the night and is when the body relaxes into a period of restoration. This sleep stage is thought to play an important role in growth, memory, and immune function. Why SWS increases with alcohol consumption (at least in the early parts of sleep) isn’t quite clear, but is probably related to alcohol’s depressant and inhibitory effects on the brain. This would make sense as levels of alcohol in the blood would be highest in the earlier parts of the night and decrease as sleep progresses.How can you apply these findings?Avoid alcohol close to bedtime. In this study, the participants’ pre-sleep breath alcohol levels were between 0.038 and 0.087 (the average was 0.066 or just below the legal limit) and they finished their last drink around 1 hour before bedtime. This is way too close for comfort if you want to avoid alcohol’s effects on sleep. Don’t go to bed with alcohol in your system.I think a minimum of 3 hours seems prudent. One alcoholic drink takes about an hour to metabolize and leave your system. So 3 drinks would require about 3 hours to metabolize, more or less. This is why I advocate day drinking (kidding, folks).If you don’t drink, then you’ve got nothing to worry about.Cheers, and thanks for reading. I’ll see you next Friday.~Brady~The VO2 Max Essentials eBook is your comprehensive guide to aerobic fitness, how to improve it, and its importance for health, performance, and longevity. Get your copy today and use code SUBSTACK20 at checkout for a 20% discount. You can also grab the Kindle eBook, paperback, or hardcover version on Amazon.Examine.com: Examine is the largest database of nutrition and supplement information on the internet. This is a public episode. If you'd like to discuss this with other subscribers or get access to bonus episodes, visit www.physiologicallyspeaking.com/subscribe