Until recently, it was widely believed that the main function of sleep was to prevent sleepiness during the day, and the health effects of sleep deprivation were largely unknown. It is now thought that adults require approximately 8 hours of sleep each night, and negative effects are more likely to present in individuals that get significantly more or less than this amount.
It is worth noting that the impact of sleep deprivation reduces as individuals get older, and it is believed that elder individuals require less sleep for healthy function than children or adolescents.
Weight Gain and Obesity
Sleep deprivation is linked to weight gain and obesity in both adults and children, with sleep time less than 7 hours per night related to a higher body mass index (BMI).
Some evidence has shown a U-shape curve for sleep duration and obesity, with individuals that have approximately 8 hours sleep per night with the lowest BMI and both higher and lower sleep times not increase in weight gain.
Diabetes and Impaired Glucose Tolerance
Loss of sleep has been associated with impaired glucose tolerance and diabetes. These conditions are marked by an abnormally high level of glucose in the blood for an extended period of time, following a meal or diagnostic injection of glucose.
One study found that middle-aged adults that self-reported to have 5 hours or less of sleep per night were 2.5 times more likely to suffer from diabetes. Diabetes is also closely linked to obesity, and the increased risk of diabetes may be associated with weight changes observed in sleep deprivation.
Some epidemiological research has also linked deprivation of sleep to increased risk of cardiovascular events, such as myocardial infarction and stroke. It is unclear, however, if this is a direct result of reduced sleep quality or as a consequence of increased incidence of obesity and diabetes.
The mechanism that is responsible for increasing the risk of cardiovascular events may involve changes in blood pressure, the sympathetic nervous system or impaired glucose tolerance.
Mood and Behavior
Changes in mood and behavior are usually the first signs that become evident in individuals with sleep deprivation, even in early stages of the condition.
Adults that are affected by chronic sleep deprivation are more likely to report symptoms of depression, anxiety and mental distress, to consume high amounts alcohol and have a higher risk of suicide. However, it remains unclear if chronic sleep deprivation causes these effects or if changes in mood and behavior are responsible for insomnia and the presentation of sleep deprivation.
Cognition and Motor Functions
The effects of sleep deprivation on the cognitive performance of individuals are only beginning to be understood with current sleep research.
It is known that lack of sleep is linked to slower reaction times and greater variability in individual performance, which is particularly evident fro activities that require a high level of alertness, attention and vigilance. However, the long-term effect of sleep deprivation on memory and perception is less clear.
It is also believed that sleep is needed to strengthen the immune system and the defense of the body against bacterial and viral infection. This link has been suggested due to observations of increased sickness in individuals that are sleep deprived, both over the short-term and long-term.