The biology of human sleep timing, like that of other mammals, changes as we age.
This has been shown in many studies. As puberty begins, bedtimes and waking times get later. This trend continues until 19.5 years in women and 21 in men. Then it reverses. At 55 we wake at about the time we woke prior to puberty. On average this is two hours earlier than adolescents. This means that for a teenager, a 7 a.m. alarm call is the equivalent of a 5 a.m. start for people in their 50s.
Precisely why this is so is unclear, but the shifts correlate with hormonal changes at puberty and the decline in those hormones as we age.
The amount of sleep teenagers get varies between countries, geographic region, and social class, but all studies show they are going to bed later and not getting as much sleep as they need because of early school starts.
In the United States, the observation that teenagers have biologically delayed sleep patterns compared with adults prompted several schools to put back the start of the school day.
An analysis of the impact by Kyla Wahlstrom at the University of Minnesota found that academic performance was enhanced, as was attendance. Sleeping in class declined, as did self-reported depression.
It is my strongly held view, based upon the evidence, that schools get better when we take sleep seriously.
Russell Foster is co-author of “Sleep: A Very Short Introduction.”
From Slate.com