Why can a lack of sleep at night lead to obesity? Short sleep increases appetite, which, in turn, increases the risk of obesity. Due to insufficient sleep, the body mistakenly believes that it does not have enough energy. Depending on the individual characteristics of a person, the duration of a healthy night's sleep is 5-10 hours. Primary school students should sleep 8-12 hours, secondary - 6.5-10 hours. Most adults need 7-8 hours of sleep.