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Myth Conceptions by Dr Karl S. Kruszelnicki - Age Good Weekend, February 10, 2007
You may think that the infinite ability of teenagers to sleep in on weekends is all down to attitude, but this altered sleep pattern isn't about being bone-lazy or antisocial, it's about biology.
New born babies sleep, in a series of naps, for about 16-18 hours a day. By age five, this is down to about 11 hours, and continues to drop with age - until puberty starts. Puberty lasts to about 17 years and five months in boys, and 16 years in girls, as measured by the end of bone growth. But adolescence continues for a few more years.
During adolescence, the natural circadian rhythm is mightily interfered with and there is a delay in the onset of sleep, probably doe to the later release of melatonin. So a teenagers claiming to be not tired at 11pm is probably being truthful. Another biological change is that adolescents need more sleep - between 9 and 10 hours every night. Indeed, one marker of the end of adolescence is the switch to the shorter and earlier adult sleep hours. This happens, on average, at 19 years and 5 months in women, and 20 years and 9 months in men.
The teenage years are very messy, in terms of sleep. An early bedtime is, in most cases, simply fighting biology. Adolescents need 9 to 10 hours of sleep, but often start school early. Typically and adolescent, going from holidays to regular school, will sleep for 2 hours fewer on weeknights, and try to make it up on weekends. So your average high-school student sleepwalks through their school day, in a semi permanent state of sleep deprivation.
Various studies have shown that this sleep deprivation is linked to rebellious behaviour, depressive symptoms, cigarette smoking, obesity, anxiety disorders and poor school marks. Indeed, being tired while taking an IQ test can drop about 7 points off your score - and can do the same for regular exams. Also, about 20% of road deaths are caused by micro sleeps related to tiredness - and about half of all such fatigue-related road deaths happen to those aged 16-25.
Another study looked at so-called REM sleep, during which humans do most of their dreaming and which usually happens about 70 to 100 minutes after falling asleep. About half of the high-school students studied were so tired that, when give the opportunity to sleep at school in mid-morning, they dropped into REM sleep within a few minutes.
So what can help? Well, adolescents should avoid caffeinated drinks and not have a computer or TV in their bedroom.
Dr Martin Ralph, a psychologist at the University of Toronto, recommends starting university and high-school classes at 11am.
And next time you want to chide your teenager with a well-worn cliche, in the interests of scientific credibility don't make it, " Early to bed and early to rise ..."