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Importance of Sleep

First off, some facts on sleep, sleep is divided into two main categories:
rapid eye movement (REM)
non-rapid eye movement (NREM)

You spend most of the night in NREM sleep and gradually work towards REM sleep every 90 minutes or so. The later stages of sleep are invaluable for its benefits of restorative function. You can only get there if you cycle through the initial stages, which is why sleep quality is as important as sleep quantity.

Why is it important?
You produce most of your growth hormone when you sleep. Growth hormone (GH) appropriately named because it is essential for you to grow. Some of the benefits of getting this hormone going are:
Increases your calcium retention (to help maintain your bone mass)
Promotes fat loss
Reduces fat storage
Supports your immune system
Keep your organs operating smoothly.

GH isn’t the only hormone affected by sleep, as mentioned before your hunger controlling hormones are Grehlin and Leptin which are present in sleep and day to day. If you have gone to bed hungry and have a full night’s sleep, you’ll wake up not hungry this is down to hormones above. A study in the journal PLoS Medicine showed a strong correlation between limited sleep, high levels of hunger-inducing Ghrelin, low levels of satisfaction-inducing Leptin and obesity. Lack of sleep will make you fat. Still, this only touches on the benefits of sleep. We’re still learning how sleep mitigates aging, helps reinforce lessons in the brain and informs our natural circadian rhythms (our 24-hour physiological process). It’s pretty well understood that optimal sleep levels do wonders for all of this.

What is optimal?
Sleep needs are unique to the individual, for adults, the national sleep foundation recommends 7-9 hours. Lifestyle and activity levels play a huge factor—the harder you live, the more sleep you need—so you’ll have to figure out your own personal needs.

How does it affect the Hormones?
One lifestyle factor which may influence hormone levels and also weight is sleep. There is already a body of evidence which suggests that sleep restriction can alter hormones that control food intake via stimulation of the appetite hormone (Grehlin). While this happens suppression of hormones that that control appetite (e.g. leptin). The simple answer to this end result can mean there could be increased food intake.
A group of adults were put on a calorie-restricted diet (10 per cent less than the amount calculated to maintain their weight) [1]. For two weeks, each of the participants was given a total of up 8.5 hours sleep a night. On another occasion, the same individuals spent a two-week stint in which sleep was restricted to no more than 5.5 hours a night. Actual sleep time, as well as body weight and composition was assessed over the both of the two-week periods.
During the longer sleep phase, average duration of sleep was about 7 and a half hours. In the shorter sleep phase, it was about 5 and a quarter hours.
The weight loss for both phases was about the same (an average of 3 kg/6.6 lbs). But the really interesting thing was that while during the longer sleeping time about half this weight loss was in the form of fat (3.1 lbs), during the shorter sleep time fat loss was only half this loss (1.3 lbs) was fat. Shorter sleep duration reduced the proportion of weight lost in the form of fat by more than half (55 per cent). Fat-free losses were greater in this group, and much of this would come in the form of muscle.
In short, less sleep led to smaller fat losses and greater attrition of muscle.

Why short sleep should have this effect is probably complex, and almost certainly involves hormonal changes. Another hormone that might play an important role here is cortisol. This hormone is secreted in response to stress, and plays a very important part in the stress response. Higher levels of this hormone can be secreted when sleep is cut shorter.
One of cortisol’s effects is to encourage ‘catabolism’, which essentially means the breakdown of body tissues. And one potential target here is muscle, particularly those in the limbs. Cortisol also, however, encourages deposition of fat, specifically in and around the abdomen and trunk. The changes seen with less sleep is common are consistent with raised cortisol levels, though this study did not look at this specifically.
While we may not know how shortened bouts of sleep alters weight loss, this study does strongly suggest that adequate sleep is important for healthy body composition. It’s another piece of evidence which shows how good sleep habits may enhance health and wellbeing.

1. Nedeltcheva AV, et al. Insufficient Sleep Undermines Dietary Efforts to Reduce Adiposity. Ann Intern Med. 2010;153(7):435-41