Teens lose night sleep by nature

Scientists have confirmed what parents of teenagers have always suspected: Adolescents are out of sync with the rest of the world.

Most teens probably don't get enough sleep and suffer in their school work because their internal clocks make them night owls, according to a study published Tuesday.

Researchers in Australia showed that the average teenager misses more than an hour of sleep each night and are forced to wake up 2.5 hours earlier than their natural rhythms would dictate.

High school students with a late-night "circadian preference", as the biologically-driven cycle is called, reported doing more poorly in school, and feeling more frequently depressed and unhappy.

"For all people, there is a genetic disposition to being either a 'morning lark' or a 'night owl'," explained lead author Suzanne Warner, a professor at Swineburne University of technology in Hawthorn, Australia.

When hormonal changes kick in at the start of adolescence, young people start to stay up later and -- given the chance -- wake up later too, she said.

Most of the students in the study were such "evening persons," she said.

"Teenagers find that they are most alert in the evening and do not feel sleepy until later, and so find it difficult to get enough sleep during school term," she added.

The key is melatonin, a hormone that signals to the body that it needs rest and sleep. In teenagers entering puberty, it is released later and later in the evening.

There are also environmental factors that contribute to the problem, she said.

Ambient light tends to minimize the amount of melatonin secreted, and the constant use of computers could keep adolescents up past their natural bedtime, even after lights are turned out.

"One thing parents can do is to lower the lights, and switch off computers and televisions an hour before bedtime," advised Warner.