We all need to sleep. All living beings need to sleep. This applies to creatures living in water as well. Even marine creatures which appear to move all the time go to sleep by shutting down one half of their brains in a phenomenon called hemispheric sleep. It is clear that sleep is essential and plays an important role in the well being of living creatures. In spite of its importance, the phenomenon is shrouded in mystery. Even as we sleep, there are regions in the brain which continue to be active. These regions belong to the autonomic nervous system which controls our involuntary activities. This means that these activities are not under our control. The rhythmic contraction of the heart enabling blood to be pumped continuously is the best example. The heart does not function under our orders.
Normally, human beings are required to sleep between six and eight hours. Anything more or, less than this is detrimental to health. Even a single night’s sleep deprivation could produce noticeable changes in body chemistry. Normally, there are five stages in sleep. The first four are believed to have a role in maintaining normal metabolism and also promote learning and memory. The fifth and final stage is called REM (rapid eye movement) sleep. This final stage has role in mood control and formation of emotional memories. Sleep deprivation on a regular basis, which is very common in shift workers, can produce serious diseases including cardiovascular disease, diabetes, obesity and neurodegenerative disorders.
Role of Ghrelin
Weight gain and obesity are the consequences of sleep deprivation. There are several mechanisms at work leading to gain in body weight. Sleep deprivation can lead to an increase in the circulating levels of the hormone called ghrelin. This hormone is secreted from the stomach and has been called the hunger hormone because this hormone has the ability to stimulate the appetite. Thus, when somebody does not get enough sleep, his appetite increases as a result of increased secretion of ghrelin.
Role of stress
Sleep deprivation also causes the blood levels of cortisol to go up. This hormone has been called the stress hormone because its levels go up whenever there is stress. Sleep deprivation is a form of stress. When individuals are under stress, they tend to eat more, leading to weight gain. One of the causes for obesity is the continual presence of stress. Continuous presence of stress can exhaust the adrenal glands, thereby drastically reducing the secretion of cortisol and this can produce obesity.
In addition to above mechanisms, an additional factor is also at play. Sleep deprivation results in the slowing of metabolism. When the metabolism is on the slow side, this results in decreased energy consumption. When this happens on a regular basis, the calorie retention in the body would be sufficient to produce significant increase in body weight.