The link between sleep and performance is a well known, scientifically proven fact. Much is often said about the fact that sleep is an anabolic state because it increases the process of growth and contributes to the restoration of the immune, nervous, and muscular systems. It is also responsible for maintaining normal levels of cognitive skills such as speech, memory, innovative, and flexible thinking. In other words, sleep is an essential part of life.

But what happens when you don’t get enough sleep? What are the negative affects of sleep deprivation, a condition that is becoming more and more common in today’s high pressure, stressful and hectic life? 
For a start, recent studies have found that sleep deprivation, also referred to as a cumulative sleep debt, not only affects immune and brain function but also negatively impacts a person’s physiology.
These studies found that sleep deprivation can slow glucose metabolism by as much as 30 to 40%. This reduction is caused by increased central nervous system activity, which becomes more active as a result of sleep deprivation, inhibiting the pancreas from producing adequate insulin, the hormone the body needs to digest glucose. Just a week of sleep deprivation reduces the ability of a young person’s body (18 – 24 years) to synthesise glucose, reducing this bodily function to the same extent as an elderly person. Glucose effectiveness, defined as the ability of glucose to mediate its own disposal independently of insulin, was also 30% lower in the sleep-deprived subjects.
Reduced levels of sleep will also trigger the endocrine system to produce greater levels of the stress hormone cortisol. Because cortisol is catabolic, elevated levels may interfere with tissue repair and growth causing muscle loss. Over time, this could prevent a bodybuilder from responding to heavy training and lead to  overtraining and injury. A cortisol imbalance can also lead to a hardening of the arteries, something that can cause a heart attack. In addition, very high cortisol levels increase the storage of fat, loss of bone mass and can also cause depression, hypertension, insulin resistance (as the cells in the body lose the ability to accept insulin), and lower growth hormone and testosterone production.
A lack of good sleep, especially at a younger age, could drive down growth hormone (GH) levels prematurely as GH is secreted during the first round of deep sleep. Lower GH levels accelerate the fat-gaining process and reduces the body’s ability to make anabolic gains. As both men and women age, they naturally spend less time in deep sleep, which lowers GH secretion even further. Research also indicates that sleep deprivation lowers serum testosterone levels, which would promote the loss of muscle mass and increase fat deposits.
Sleep deprivation can also increase carbohydrate cravings as it negatively affects the production of a hormone called Leptin. This hormone controls satiety, the process that is responsible for telling the body when it is full. However, with decreased production of this hormone your body will crave more calories, especially in the forms of carbohydrates, even though the body’s requirements have been met.