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How much sleep is enough? Is how sleepy you feel a good judge
of whether or not you are getting enough sleep? If you get less
sleep than some ideal amount but you feel fine, could you be damaging
your health anyway? Are we getting less than we used to? Recent
research provides some surprising answers.
Adults typically need seven to nine hours of sleep each night
to feel fully rested and function at their best. However, Americans
are getting less sleep than they did in the past. A 2005 National
Sleep Foundation poll found that Americans averaged 6.9 hours
of sleep per night, which represents a drop of about two hours
per night since the 19th century, one hour per night over the
past 50 years, and about 15 to 25 minutes per night just since
2001.
Unfortunately, we are not very good at perceiving the detrimental
effects of sleep deprivation. Researchers at the University of
Pennsylvania restricted volunteers to less than six hours in bed
per night for two weeks. The volunteers perceived only a small
increase in sleepiness and thought they were functioning relatively
normally. However, formal testing showed that their cognitive
abilities and reaction times progressively declined during the
two weeks. By the end of the two-week test, they were as impaired
as subjects who had been awake continuously for 48 hours.
Moreover, cognitive and mood problems may not be the only consequences
of too little sleep. Researchers at the University of Chicago
have shown that too little sleep changes the bodys secretion
of some hormones. The changes promote appetite, reduce the sensation
of feeling full after a meal, and alter the bodys response
to sugar intakechanges that can promote weight gain and
increase the risk of developing diabetes. Since then, multiple
epidemiological studies have shown that people who chronically
get too little sleep are at greater risk of being overweight and
developing diabetes.
A recent review by a team from Case Western Reserve University
and Harvard Medical School found that all of the large studies
that followed people over time agreed that short sleep duration
was associated with future weight gain. This connection was particularly
strong in children: all 31 studies in children showed a strong
association between short sleep duration and current and future
obesity. For example, a study by Susan Redline and colleagues
at Case Western Reserve University School of Medicine showed an
inverse correlation between sleep duration and obesity in high-school-age
students. The shorter the sleep, the higher the likelihood of
being overweight, with those getting six to seven hours of sleep
more than two and a half times as likely to be overweight as those
getting more than eight hours.
The likely connection between sleep deprivation and obesity comes
on top of previous research linking sleep deprivation with increased
risk of high blood pressure and heart disease.
The good news is that these effects can be reversed by getting
an adequate amount of sleep. The University of Chicago study on
sleep duration and appetite found that allowing the study subjects
to sleep 10 hours for two consecutive nights returned the hormones
to normal levels and lowered hunger and appetite ratings by almost
25 percent.
We have many opportunities to avoid sleeplights, electronic
devices, and other entertainment offer round-the-clock temptations.
But we must recognize the impor-tance of sleep and make it a priority
to get enough. It is a lot easier to prevent weight gain, diabetes,
high blood pressure, and heart disease by getting enough sleep
than it is to treat these problems once they develop.
Epstein is a Sleep Physician at Harvard Medical School, author
of The Harvard Medical School Guide To A Good Nights Sleep,
Published By McGraw-Hill, and is the Chief Medical Officer for
Sleep Healthcenters in Boston.