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Sleep and Hormones

May 15, 2013

Sleep Deprivation and its Effects on Hormones

The hormones that are most frequently stated to be affected by sleep are: Insulin, Androgens, growth hormone, and cortisol.

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 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.

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.

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?

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.

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 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.

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 is that sleep deprivation eventually 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.

Metabolic Rate

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.

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).

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