Sleep duration averages between 7 and 8 hours in human adults. There are, however, individual differences. Most studies show that sleeping less than 6 hours constitutes sleep deprivation whereas sleeping more than 9 hours is excessive.
Body weight is a function of two factors: caloric intake and expenditure. When in equilibrium, weight remains constant. Net weight gain or loss results when this balance is tilted toward intake or expenditure of calories. This shift in balance depends on a complex interaction of biological, psychological and environmental factors.
Sleep is a state of zero intake and reduced energy expenditure. Although no physical activity happens, several energy dependent processes still continue to occur in the body during sleep. Two hormones, cortisol and growth hormone are released during sleep. Their levels steadily rise throughout sleep. The purpose is to prevent hypoglycaemia or an abnormally low glucose level. Normally, the levels of these two hormones return to baseline during waking hours.
Sleep deprivation causes a dysregulation in cortisol levels. A higher than normal cortisol level is seen in individuals who sleep less than their body needs. This abnormal elevation makes it difficult for the body to dispose of glucose which in turn causes fat accumulation. In addition, sleep deprived individuals have a higher tone of the sympathetic nervous system. New research has also shown that sleep loss causes low grade inflammation. The net effect of all these changes is this: weight gain.
Leptin and ghrelin are two important molecules related to appetite. Leptin induces feelings of satiety whilst ghrelin causes feelings of hunger. During sleep, the levels of these hormones increase. Additionally, leptin shows a certain diurnal variation which means its levels fluctuate during 24 hours. Sleep deprivation disrupts this rhythm of leptin. Besides, leptin concentrations are lower than normal in sleep deprived subjects. A decrease in leptin function is associated with weight gain.
Orexins are a new group of molecules released from neurons in certain parts of the brain. In general, they are related to both increased energy intake and expenditure. Thus they promote wakefulness rather than sleep. Although their exact mechanism of action is not known, it is clear that they play a crucial role in the sleep-wake cycle and energy metabolism.
The benefits of getting adequate sleep are by no means limited to weight control. Sleep impacts most aspects of physical and emotional well-being. If you have a sleep problem, you should try some simple rules of sleep hygiene.
Going to bed and waking up at the same time every day, avoiding distracting such as TV and electronic gadgets before sleep, having no coffee close to bedtime, reducing emotional stress, and similar tips may be all you need to get a restful night’s sleep. However, if they do not work, it is best to seek professional help. Sleep well!