Sleep: What the Research Actually Says
Written on May 9, 2013 at 5:32 pm, by Eric Cressey
As a complete workaholic, I have a tremendous interest in the acute and chronic effects of sleep deprivation on both performance and health. And, as a performance coach to many athletes who generally go to "work" from 1pm-1am each afternoon/evening and often consume far too much caffeine, I'm always looking for good material to pass along their way in hopes of helping them to realize how important sleep really is. In this great guest post, Sol Orwell and Kurtis Frank provide just that. It's a long read, but 100% worth it. Enjoy! – EC
Sleep is a fun topic. Every few months or so, someone will put up a post talking about how important sleep is, how you need it, how if you don’t get enough of it you will get fat and disgusting and huge, yadda yadda yadda.
We’re not here to dispute that. What we are here to do is take an investigative look; sleep is entering the realm of “say something enough times, and it has to be true.” You’ll be hard-pressed to find any recent articles that have actually looked at the evidence surrounding sleep quality and quantity and how they affect your body. Mostly, the evidence we have is purposely restricting sleep in people and seeing what happens.
Prepare for some truthiness (we’ve also inserted some blockquotes to help guide you through).
Sleep Deprivation and its Effects on Hormones
The hormones that are most frequently stated to be affected by sleep are:
Insulin – one of the most misunderstood hormone there is (see James Krieger’s fantastic analysis on insulin)
Androgens – the muscle-building hormones
Cortisol, the “stress” hormone
Sleep deprivation doesn’t seem to affect insulin levels much, but there is definitely a decrease in insulin sensitivity in the fat cells and liver1,2. This decrease in sensitivity can happen as easily as getting half your normal amount of sleep for less than a week3,4 or even losing 90 minutes over a few weeks5. This lack of sleep, coupled with decreased sensitivity, is a risk factor for the development of type II diabetes.
Thankfully, these effects are quickly normalized upon recompensatory sleep.
The implications of reduced insulin sensitivity, beyond an increase in diabetes risk, are not too clear for an otherwise healthy person, as the decrease in insulin sensitivity affects all measured tissue (adipose, muscle, and liver) and is just due to impaired signalling through the insulin receptor.
Sleep deprivation reduces insulin sensitivity and glucose tolerance. This happens even after mild deprivation, but normalizes quickly once you’ve had enough rest.
Androgens and Testosterone
Testosterone is known for being affected by poor sleep (on a related note, you tend to sleep worse as you age, and this exacerbates sleep deprivation problems)6,7. Studies have shown that getting three fewer hours of sleep for five days reduced testosterone by over 10%8, whereas another study showed a 30.4%9 decrease! These reductions all happened within 24 hours of sleep deprivation10,11. Similar to insulin, getting enough rest quickly reverses this decline.
Sleep deprivation is associated with reduced testosterone. Akin to insulin, it normalizes once you get enough rest.
Growth hormone is actually a surprise in regards to sleep deprivation. For starters, we know that a large pulse of growth hormone occurs shortly after sleep begins, and in otherwise healthy young men, this accounts for roughly 50% of daily secretion. So would missing out on sleep impair growth hormone?
It depends on the duration of sleep.
Absolute deprivation of sleep for multiple nights can effectively suppress growth hormone. But neither an irregular sleep cycle (like a shift worker’s)12 nor only sleeping for four hours a night13 will adversely affect whole-day exposure to GH. It seems that the body compensates during daylight hours, and what is missed out on at night is adequately replaced during waking hours in those that are sleep-deprived.
Now, it is possible that the altered secretion patterns of GH can come with changes in its effects. However, the overall pattern is still pulsatile in nature (just biphasic rather than monophasic) and unlikely to be a huge issue.
Getting less sleep or having perturbed sleep changes the GH cycle, but does not reduce overall exposure to GH, as the body seems to compensate during waking hours.
Cortisol is the hormone that mediates the process of waking up, and under normal rested conditions, it’s elevated in the morning (to wake you) and suppressed in the evening (so you can fall asleep). It isn’t necessarily a bad hormone (the anti-inflammatory and fat-burning properties sound nice), but elevated cortisol also tends to be somewhat catabolic to muscle tissue, as well as being an indicator of other stress-related issues.
Sleep deprivation both dysregulates and increases whole-day exposure to cortisol. Imagine a graph where a line goes from high on the left to low on the right, and label it “what cortisol should do over time.” Sleep deprivation turns that line into a straight horizontal line, and then raises it up a tad on the Y-axis.
Interestingly, past studies were misguided a bit since they were only measuring morning cortisol concentrations and they kept on noting a decrease! Most recent studies that measured 24-hour exposure noted an increase – some as high as 50% – following four hours of deprivation each night for a week in otherwise healthy men.
Cortisol normally is high in the morning and low in the evening, but sleep deprivation normalizes this difference (lowering morning levels, increasing evening levels) and increases overall exposure to cortisol over a full day.
Sleep Deprivation and Physical Activity
Sleep deprivation has been noted to impair sprint performance and cardiovascular endurance14,15. There is conflicting evidence here: tests on cycle ergometers did not note much of an effect16,17, and the one study to assess weightlifting performance also failed to find any adverse effect18.
Despite these mixed reports on sleep deprivation, acute sports performance is enhanced by caffeine and/or creatine supplementation during a state of acute sleep deprivation. The latter only seems to apply to things that require a high degree of coordination and mental processing19.
It’s important to note that these studies had participants just skip sleep for one night. Real-world application is more chronic; you tend to lose a few hours every night, and it adds up. The impracticality of these studies makes it very hard to make solid conclusions.
(Note from EC: anecdotally, I could always “get away with” one night of sleep deprivation and then still demonstrate “normal” strength the next day. If I missed out on sleep two nights in a row, though, my in-the-gym performance went down the tubes after the second night)
Missing sleep for one night may or may not have adverse effects on performance, as the literature seems pretty split. There is a lack of research on realistic situations for chronic sleep deprivation.
Sleep Deprivation and Body Composition
Food Intake and Hunger
One of the more talked about effects of sleep deprivation as it pertains to body composition is that it somehow makes you eat a ton more food and then you get fat.
The general idea (based on rat studies) is that sleep deprivation eventually (after five days or so) leads to increased food intake, but oddly this is not met with an increase in body weight; absolute sleep deprivation paradoxically causes fat loss and mild sleep deprivation just prevents weight gain.20 The increase in food intake is probably because of an exaggerated response to orexin, a wakefulness-promoting hormone that positively modulates hunger. Orexin increases as one is awake longer, causing more food intake as a side effect.21 Orexin also positively mediates energy expenditure, but it is not known if we can credit this for the observed weight-maintenance effects.
More practically speaking, studies in humans have noted an increased food intake of roughly 20-25% following a few hours of sleep deprivation for four days22,23. This is likely due to the brain’s response to food intake being enhanced, thus making food more hyperpalatable24,25.
It is unclear how sleep deprivation affects weights in humans. There is a very well-established correlation in society between obesity and sleep disturbances, but the studies currently conducted in people on weight loss programs with sleep deprivation control for food intake.
Sleep deprivation appears to increase food intake, likely due to the increased “pleasure response” to food. Paradoxically, this increased food intake might not be linked to more weight gain (rat studies confirm, human studies are somewhat unclear).
It’s harder to make sense of the effects of sleep deprivation on metabolic rate. One study found that getting three fewer hours of sleep per day for two weeks resulted in a 7.6% reduction in metabolic rate26, whereas other studies showed no decrease22,27. To make it even more confusing, one study (on adolescent boys) found that less sleep resulted in more calories burned28; the participants burned more (being awake longer) and consumed less (decreased appetite).
In rats, chronic sleep deprivation is also known to greatly increase both food intake and the metabolic rate, resulting in weight loss (albeit a ton of other side effects such as lethargy, impaired cognition, and an aged visual appearance probably make sleep deprivation a bad diet strategy).29
So ultimately, it doesn’t appear that there is much evidence that poor sleep reduces the metabolic rate. More likely, being “tired” from lack of sleep tends to result in less physical activity30 and a possible increase of food intake could shift the balance of “calories in versus out” towards a surplus.
There is one other interesting study that controlled for food intake and noted no differences in weight loss between groups (sleep deprived people and control both subject to intentional weight loss programs). This same study showed more lean mass lost and less fat mass lost in the sleep-deprived relative to control31.
Overall, it does not appear that a reduction in sleep directly suppresses the metabolic rate, but it may do so indirectly via reduced physical activity. Regardless of the metabolic rate, sleep deprivation during periods of fat loss may result in more lean mass lost and less fat mass lost than if one were fully rested.
Enhancing Sleep Quality
It seems that getting an adequate amount of sleep each night is quite important for those concerned with athletics and/or body composition. It would be a tad abrupt to just leave off on the importance of sleep without saying how to improve sleep, so the following are some tips that can be used to enhance sleep quality.
Timing Food Intake
Food intake can be quite effective in influencing the circadian rhythm: One way to avoid jet lag involves having a high-protein breakfast intermittently for three days (separated by low-calorie “fasting” days) at your destination’s time; the final meal is breakfast eaten after having arrived. This high-protein meal at your destination’s breakfast time should be able to reset your circadian rhythm. This is known as the Argonne Diet, and although it lacks scientific evidence to support it, the anecdotes are promising.
It appears to play on the interactions between dietary protein and orexin, a wakefulness-promoting hormone highly involved in the circadian rhythm.31
Conversely, dietary carbohydrates may be able to promote relaxation (somewhat indirectly) secondary to an increase in serotonin synthesis, which then converts to melatonin. Since the conversion requires darkness to occur, this might mean a small serving of carbohydrate prior to sleep can promote restful sleep while focusing dietary protein earlier in the day might also work to regulate the sleep cycle.
Light Exposure or Deprivation
Both light exposure (blue/green or white lights; fluorescent or sunlight) and dark exposure (either absolute darkness, or an attenuation of white light into pink/red dim lights) can aid in sleep-cycle regulation. Both dark and light exposure have been investigated for restoring altered circadian rhythms seen with jet lag.32,33
The perception of light via the retina actively suppresses the conversion of serotonin into melatonin, and appears to have other neurological effects that promote wakefulness (in the morning) or otherwise impair sleep. Reddish lights appear to be less detrimental to sleep quality, and it is sometimes recommended to dim lights or switch to red lights in the evening to facilitate sleep quality.
For those of you at the computer frequently, this can be demonstrated with the downloadable software known as f.lux, which fades your computer screen to pink and reduces the brightness without affecting readability at a preset time every day.
Regulating your light exposure in the morning and evening may facilitate a more normal circadian rhythm and sleep quality. If light cannot be avoided outright, a transition from white light to red light at night may be helpful.
Supplementation to target sleep quality tends to stem from melatonin, which is a highly reliable and effective anti-insomniac agent that can reduce the time it takes to fall asleep. It is unlikely to do anything if you do not have problems falling asleep, but otherwise is a quite important and cheap supplement. The above light- and meal-manipulation strategies tend to work via melatonin manipulation anyways, and supplementation is an easy way to circumvent it.
Beyond melatonin, other possible options include generally relaxing compounds (lavender and l-theanine) or other endogenous agents that seem to regulate sleep (oleamide being the latest up-and-comer supplement). Lavender is actually an interesting option since it appears to be somewhat effective as aromatherapy as a “relaxing” scent, and aromatherapy may be the only way to continuously administer a supplement throughout sleep (via putting a few drops of lavender oil on a nearby object and continuing to breathe while you sleep).
It should also be noted that restricting stimulants or anti-sleep agents (caffeine and modafinil mostly) should be advised if sleep quality is desired. Even if caffeine fails to neurally stimulate you anymore due to tolerance, it can still screw with sleep quality.
What You Should Have Learned
That was a lot of information and studies to throw at you all at once. We’ve summed up all the relevant points:
Reduced sleep for a prolonged period of time can decrease insulin sensitivity (and thus is a risk factor for diabetes); this is normalized when proper rest is attained.
Similar to the issue of insulin sensitivity, testosterone and other anabolic hormones are acutely suppressed with sleep deprivation and normalized shortly after proper rest is attained.
There is actually mixed evidence as to whether missing a night of sleep impairs workout performance. It would be safe to say that it does not help, and could potentially hinder.
Sleep deprivation is not adverse to weight loss per se, but it can cause you to overeat or move less.
Regardless of weight loss, limited evidence suggests an adverse effect on where the weight is lost (more lean mass lost, less fat lost).
Shifting the majority of your protein towards the morning, and perhaps having a small carbohydrate-containing meal at night, should theoretically aid in maintaining a proper circadian rhythm.
Manipulating light exposure for brighter white/blue/green lights in the morning and dimmer red/pink lights (or just darkness) at night definitely does aid in maintaining a proper sleep cycle.
If needed, melatonin can be used to help with sleep latency (time required to fall asleep) and abstaining from stimulants or introducing relaxing molecules (lavender and theanine) may aid in sleep quality.
About the Authors
Sol Orwell and Kurtis Frank co-founded Examine.com in early 2011. They’ve been collating scientific research on supplements and nutrition since then, and are working on a beginner’s guide to supplements.
Note: the references for this article are posted as the first comment below.
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