Evidence shows that adults need between seven and eight hours of SLEEP each night, and regularly sleeping less than five hours a night is linked to cardiovascular problems and poor immune health. People do not belong in this group, Fu said, if they drink a lot of coffee or tea to stay awake, or need to catch up on sleep during weekends or holidays. If they have to limit their sleep for a few days, they can boost their energy with these methods. However, there are those who side with Klasko and think that some short sleepers may, in fact, be fine.
People with sleep apnoea, who sometimes sleep long hours, may be in a totally different category due to poor sleep quality. If you have trouble sleeping or are unable to sleep more than a few hours a night, talk to your doctor to make sure you are getting enough sleep. Although this group seems the most likely to avoid the problems associated with sleep deprivation, Williams cautions against taking it for granted. When forced to sit still, for example, in an MRI machine or in a dark, quiet room, those who say they feel fine are just as sleepy as those who knew they were tired all along.
Fu studies a rare and extremely lucky group who seem to be genetically inclined to sleep less, and probably need it. Devices such as Fitbits, which can monitor sleep habits, have given rise to a form of sleep perfectionism, which researchers have dubbed orthosomnia, that can also increase anxiety. Patients with poorly controlled diabetes and sleep apnoea have improved blood glucose control when treated for sleep apnoea. So proclaims Stephen Klasko, who has prided himself throughout his life on sleeping only four to five hours a night.
The strange thing about people whose bodies adapt to sleeping less than six hours a night is that, despite the obvious lack of sleep, they show no negative side effects. This is because the amount of sleep a person gets can affect certain hormones, specifically the hormones leptin and ghrelin, which affect appetite. It is possible that the amount of sleep individuals need to avoid fatigue or lack of appetite is different from the amount needed to avoid overeating, diabetes or depression. Experts also suspect that feeling tired or groggy after four to six hours of sleep is a sign that something is wrong.