Getting too little sleep or not spending enough time in rapid eye movement(REM) sleep is connected with being overweight  among children, according to a new study.    For three nights, researchers studied the sleep patterns of 335 young people, aged 7 to 17. They looked at total sleep time, time spent in REM, time it took to fall asleep. Body-mass index  was checked at the start of the study, and 45 persons in the research were overweight, while 49 were at risk of becoming overweight.    Compared to normal-weight children, those who were overweight slept about 22 minutes less per night and didn't sleep as well as them, which means shorter REM sleep, less eye activity during REM sleep, and a longer wait before the first REM period.    After more research, the researchers concluded that one hour less of total sleep was connected a double increased risk of being overweight. One hour less of REM sleep was connected with a three times increased risk. Although the reasons are still being researched, the relationship between short sleep duration  and overweight may be the result of behavioral and biological changes, which are caused by sleep loss, wrote Dr. Xianchen Liu of the Western Psychiatric Institute and Clinic in Pittsburgh and his colleagues.    They explained that sleep loss causes changes in hormone  levels that may have an effect on hunger, and less sleep also means a person has more waking hours in which to eat. Sleep loss also leads to tiredness the following day, which may lead to less physical activity and fewer calories burned. Which is NOT the reason why sleep loss causes the risk of being overweight?
It changes levels of hormone, which may lead to hunger. It means more hours to work or study, so people have to eat more. It makes people feel tired, so they are unwilling to be physically active. It gives people more time to stay awake, during which they can eat more.