Teenagers to benefit when schools start classes later

Starting classes at middle schools and high schools no earlier than 8.30am would help students arrive alert, healthy and ready to learn, US sleep medicine specialists said.

"The American Academy of Sleep Medicine recommends that teens between 13 and 18 should sleep eight to 10 hours a night on a regular basis to promote optimal health," lead author Nathaniel Watson said.

"Biology and school start times may share the blame for teen sleep loss. A natural shift in the timing of the body's internal 'circadian' clock occurs during puberty, and as a result, most teens have a biological preference for a late-night bedtime," said Dr Watson, a sleep specialist at the University of Washington in Seattle.

Studies showed that short sleep in adolescents is associated with poor school performance, obesity, metabolic dysfunction and increased depressive symptoms, among others, the Journal of Clinical Sleep Medicine said.