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The Science Of Sleep: What the Research Actually Says – Written By Sol Orwell

There are few topics as well accepted as “sleep” – every week someone influential will tweet “get your sleep! It’s as important as diet/exercise.” This isn’t an article disputing that instead it is an investigative look at what the actual research says. We are going to take a gander at the research conducted on sleep deprivation, and make evidence-based conclusions on how sleep affects you and your performance.

It may get heavy at times, but we’ve provided summaries for each section.

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Photography: Rich Baker

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
  • Androgens – The muscle-building hormones
  • Growth Hormone
  • Cortisol – The “stress” hormone

Insulin

Sleep deprivation doesn’t seem to affect insulin levels much, but there is definitely a decrease in insulin sensitivity in the fat cells and liver (1,2). This decrease in sensitivity can happen as easily as getting half your normal amount of sleep for less than a week (3,4) or even losing 90 minutes over a few weeks (5). 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.

Summary

Not getting enough sleep reduces insulin sensitivity and glucose tolerance. Even a little bit of lost sleep can have this effect, but it goes away once you get enough sleep.

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 3 fewer hours of sleep for 5 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 deprivation (10,11). Similar to insulin, getting enough rest quickly reverses this decline.

Summary

Not getting enough sleep is linked to reduced testosterone. Just like insulin, testosterone normalizes once you get enough sleep.

Growth Hormone

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?

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 4 hours a night (13) 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.

Summary

Not getting enough sleep changes the GH cycle, but it does not decrease your full day’s GH – your body compensates during waking hours.

Cortisol

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 on the Y-axis a tad. 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 4 hours of deprivation each night for a week in otherwise healthy men.

Summary

Cortisol is usually high in the morning and then low in the evening. Not getting enough sleep dampens this high/low wave, and results in more exposure to cortisol over a full day.

Sleep Deprivation and Physical Activity

Sleep deprivation has been noted to impair sprint performance and cardiovascular endurance (14,15). There is conflicting evidence here: Tests on cycle ergometers did not note much of an effect (16,17), and the one study to assess weightlifting performance also failed to find any adverse effect (18). 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 processing (19). 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.

Summary

Not getting enough sleep (for a single night) should not have much of a negative effect on athletic performance. There is little research on chronic abuse.

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 5 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 4 days (22,23). This is likely due to the brain’s response to food intake being enhanced, thus making food more hyperpalatable (24,25). 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.

Summary

Not getting enough sleep seems to result in eating more, as you respond to food more.

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Metabolic Rate

The effects of sleep deprivation on metabolic rate are harder to make sense of. One study found that getting 3 fewer hours of sleep per day for 2 weeks resulted in a 7.6% reduction in metabolic rate (26), whereas other studies showed no decrease (22,27).

To make it even more confusing, one study (on adolescent boys) found that less sleep resulted in more calories burned (28) – 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 activity (30) and a possible increase of food intake could shift the balance of “calories in versus out” towards a surplus.

Nutrient Partitioning

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.

Summary

Overall, it does not seem that lack of sleep suppresses metabolic rate directly; it may do so indirectly by reduced physical activity. Furthermore, lack of sleep seems to results in less favorable body composition when cutting.

Enhancing Sleep Quality

So 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.

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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 3 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 neuropeptide 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.

Summary

To sleep better, get ample light in the morning, and less in the evening. If you cannot avoid light, transition from white to red light during night-time.

Supplementation

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 which 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:

  • Not getting enough sleep can decrease insulin sensitivity; get enough sleep, and it normalizes to baseline.
  • Akin to sleep and insulin sensitivity, testosterone is also decreased from lack of sleep; get enough sleep, and it normalizes to baseline.
  • Performance may or may not be impaired from lack of sleep. It would be safe to say that lack of sleep would not help performance.
  • Lack of sleep does not directly lead to less weight gain; you likely end up moving less, thereby decreasing caloric expenditure.
  • Lack of sleep seems to negatively impact body composition.
  • Having protein early and then carbohydrates at night could help in a better sleep cycle.
  • Brighter lights in the morning and dimmer (red/pink) at night results in a better sleep cycle.
  • Supplement with melatonin can help you fall asleep; abstaining from stimulants and taking relaxing supplements (lavender and theanine) can help the quality of your sleep.

About the Authors

Sol Orwell and Kurtis Frank co-founded Examine.com to help separate the myths from the facts when it comes to supplementation and nutrition.

References

1. Broussard JL, et al. Impaired insulin signaling in human adipocytes after experimental sleep restriction: a randomized, crossover study. Ann Intern Med. (2012)
2. Donga E, et al. A single night of partial sleep deprivation induces insulin resistance in multiple metabolic pathways in healthy subjects. J Clin Endocrinol Metab. (2010)
3. Buxton OM, et al. Sleep restriction for 1 week reduces insulin sensitivity in healthy men. Diabetes. (2010)
4. Reynolds AC, et al. Impact of five nights of sleep restriction on glucose metabolism, leptin and testosterone in young adult men. PLoS One. (2012)
5. Robertson MD, et al. Effects of three weeks of mild sleep restriction implemented in the home environment on multiple metabolic and endocrine markers in healthy young men. Metabolism. (2013)
6. Luboshitzky R, Shen-Orr Z, Herer P. Middle-aged men secrete less testosterone at night than young healthy men. J Clin Endocrinol Metab. (2003)
7. Penev PD. Association between sleep and morning testosterone levels in older men. Sleep. (2007)
8. Leproult R, Van Cauter E. Effect of 1 week of sleep restriction on testosterone levels in young healthy men. JAMA. (2011)
9. Cortes-Gallegos V, et al. Sleep deprivation reduces circulating androgens in healthy men. Arch Androl. (1983)
10. Cote KA, et al. Sleep deprivation lowers reactive aggression and testosterone in men. Biol Psychol. (2013)
11. Gonzalez-Santos MR, et al. Sleep deprivation and adaptive hormonal responses of healthy men. Arch Androl. (1989)
12. Brandenberger G, Weibel L. The 24-h growth hormone rhythm in men: sleep and circadian influences questioned. J Sleep Res. (2004)
13. Spiegel K, et al. Adaptation of the 24-h growth hormone profile to a state of sleep debt. Am J Physiol Regul Integr Comp Physiol. (2000)
14. Skein M, et al. Intermittent-sprint performance and muscle glycogen after 30 h of sleep deprivation. Med Sci Sports Exerc. (2011)
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16. [Enzymology. One of the basic features of diagnosis and therapy
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27. Opstad PK, et al. The thyroid function in young men during prolonged exercise and the effect of energy and sleep deprivation. Clin Endocrinol (Oxf). (1984)
28. Klingenberg L, et al. Sleep restriction is not associated with a positive energy balance in adolescent boys. Am J Clin Nutr. (2012)
29. Koban M, Swinson KL. Chronic REM-sleep deprivation of rats elevates metabolic rate and increases UCP1 gene expression in brown adipose tissue. Am J Physiol Endocrinol Metab. (2005)
30. Bromley LE, et al. Sleep restriction decreases the physical activity of adults at risk for type 2 diabetes. Sleep. (2012)
31. Marston OJ, et al. Circadian and dark-pulse activation of orexin/hypocretin neurons. Mol Brain. (2008)
32. Paul MA, et al. Phase advance with separate and combined melatonin and light treatment. Psychopharmacology (Berl). (2011)
33. Boulos Z, et al. Light visor treatment for jet lag after westward travel across six time zones. Aviat Space Environ Med. (2002)

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