(By Till Roenneberg, Washington Post, 21 November 2012)
If shopping
on Black Friday leaves you exhausted, or if your holiday guests keep you up
until the wee hours, a long Thanksgiving weekend should offer an opportunity
for some serious shut-eye. We spend between a quarter and a third of our lives
asleep, but that doesn’t make us experts on how much is too much, how little is
too little, or how many hours of rest the kids need to be sharp in school.
Let’s tackle some popular myths about Mr. Sandman.
1.You need eight hours of sleep per night.
That’s the cliche. Napoleon, for one, didn’t believe it. His
prescription went something like this: “Six hours for a man, seven for a woman
and eight for a fool.” But Napoleon’s
formula wasn’t right, either. The ideal amount of sleep is different for
everyone and depends on many factors, including age and genetic makeup. In the past 10 years, my research team has
surveyed sleep behavior in more than 150,000 people. About 11 percent slept six
hours or less, while only 27 percent clocked eight hours or more. The majority
fell in between. Women tended to sleep longer than men, but only by 14 minutes. Bigger differences are seen when comparing
various age groups. Ten-year-olds needed about nine hours of sleep, while
adults older than 30, including senior citizens, averaged about seven hours. We
recently identified the first gene associated with sleep duration — if you have
one variant of this gene, you need more sleep than if you have another.
Although it’s common to hear warnings about getting too much
sleep — and 80 percent of the world uses an alarm clock to wake up on work days
— it’s not difficult to figure out how much sleep we need. We sometimes
overeat, but we generally cannot oversleep. When we wake up unprompted, feeling
refreshed, we have slept enough. In our
industrial and urban society, we sleep about two hours less per night than 50
years ago. Like alcohol, this sleep deprivation significantly decreases our
work performance and compromises our health and memory.
2. Early to bed and early to rise makes a man healthy,
wealthy and wise.
Benjamin Franklin’s proverbial praise of early risers made
sense in the second half of the 18th century, when his peers were exposed to
much more daylight and to very dark nights. Their body clocks were tightly
synchronized to this day-night cycle. This changed as work gradually moved
indoors, performed under the far weaker intensity of artificial light during
the day and, if desired, all night long.
The timing of sleep — earlier or later — is controlled by
our internal clocks, which determine what researchers call our optimal “sleep
window.” With the widespread use of electric light, our body clocks have
shifted later while the workday has essentially remained the same. We fall
asleep according to our (late) body clock, and are awakened early for work by
the alarm clock. We therefore suffer from chronic sleep deprivation, and then
we try to compensate by sleeping in on free days. Many of us sleep more than an
hour longer on weekends than we do on workdays.
My team calls this discrepancy between what our body clocks
want and what our social clocks want “social jet lag.” This is most obvious in
teenagers. Their tendency to sleep longer is biological, not because they’re
lazy, and it reaches its peak around age 20. Studies show that teenagers who
sleep later and start school later exhibit improved academic performance,
higher motivation, decreased absenteeism and better eating habits. Yet many cultures reward people who start
work early, even if they’re operating on reduced sleep. As a result, many
successful people are short-sleeping early-risers such as Margaret Thatcher and
Bill Clinton. Fortunately for those of us who like to hit the snooze button,
success is not restricted to early birds. Albert Einstein and Elvis Presley,
for example, were late sleepers.
3. Exercise helps you sleep.
Exercising may contribute to falling asleep earlier, and it
certainly helps us sleep soundly through the night. But it’s light, not
physical activity, that proves the German proverb “Fresh air makes you tired.”
Exercise often means being outside and getting more light — on average, 1,000
times more than indoor levels. Exposure to sunlight synchronizes our body
clocks with daylight.Sleep is not only regulated by the body clock, but also by how long we were awake (also known as the buildup of “sleep pressure”). But not all waking hours are equal. We’ll get more tired skiing, for example, than sitting at a desk sending e-mail. This is one reason we sometimes lie awake at the end of a long day at the office despite utter exhaustion.
4. Sleep is just a matter of discipline.
Most parents and teachers think that if teenagers are
zombies in the morning, they just lack the discipline to go to bed early.
Although it is true that exposure to computer and television screens late at
night makes for late rising, early-to-bed teenagers will still have a hard time
getting up at the crack of dawn. Think of teenagers as early shift-workers who suffer the most social jet lag. They go to school at their biological equivalent of midnight with profound consequences for learning and memory. They suffer from sleep deprivation during the school week and certainly should be allowed to catch up on weekends. However, they should sleep with daylight coming into their bedrooms and should refrain from using light-emitting devices after 10 p.m.
5. Most couples have very different sleep habits.
We’ve all heard stories: A woman tries to sleep while her
husband is reading. Or one spouse needs to sleep in, but the other wants to
start the day. When I ask lecture audiences whether such scenarios sound
familiar, I frequently see a majority of hands go up.
But again, this is a matter of biology and genetics, not
habits and personal preference. Women generally fall asleep earlier than men,
who tend toward night owlishness. Women, however, tend to control the sleep
times in a partnership. Husbands of women who work late shifts at night, for
example, go to bed much earlier when their wives are at home than when their
wives are working late, research has found.
One finding that might be surprising, given how much time we spend in
our beds: Men and women don’t seem to give any consideration to sleep patterns
when choosing a mate.
Till
Roenneberg, a professor of chronobiology and medical psychology at the
Ludwig-Maximilians University in Munich, is the author of “Internal Time: Chronotypes,
Social Jet Lag, and Why You’re So Tired.” http://www.washingtonpost.com/opinions/five-myths-about-sleep/2012/11/21/4e1c9f44-3273-11e2-bb9b-288a310849ee_story.html
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