Why Seven Hours of Sleep Might Be Better
Than Eight
Mulberry Silk and other Sleep experts close in on the optimal night’s sleep
How much sleep do you really need?
Experts generally recommend seven to nine
hours a night for healthy adults. Sleep scientists say new guidelines
are needed to take into account an abundance of recent research in the
field and to reflect that Americans are on average sleeping less than
they did in the past.
Several sleep studies have found that seven
hours is the optimal amount of sleep—not eight, as was long
believed—when it comes to certain cognitive and health markers, although
many doctors question that conclusion.
Other recent research has shown that
skimping on a full night’s sleep, even by 20 minutes, impairs
performance and memory the next day. And getting too much sleep—not just
too little of it—is associated with health problems including diabetes,
obesity and cardiovascular disease and with higher rates of death,
studies show.
“The lowest mortality and morbidity is with
seven hours,” said Shawn Youngstedt, a professor in the College of
Nursing and Health Innovation at Arizona State University Phoenix.
“Eight hours or more has consistently been shown to be hazardous,” says
Dr. Youngstedt, who researches the effects of oversleeping.
The Centers for Disease Control and
Prevention is helping to fund a panel of medical specialists and
researchers to review the scientific literature on sleep and develop new
recommendations, probably by 2015.
Daniel F. Kripke, an emeritus professor of
psychiatry at the University of California San Diego, tracked over a
six-year period data on 1.1 million people who participated in a large
cancer study. People who reported they slept 6.5 to 7.4 hours had a
lower mortality rate than those with shorter or longer sleep. The study, published in the Archives of General Psychiatry in 2002, controlled for 32 health factors, including medications.
In another study, published in the journal
Sleep Medicine in 2011, Dr. Kripke found further evidence that the
optimal amount of sleep might be less than the traditional eight hours.
The researchers recorded the sleep activity of about 450 elderly women
using devices on their wrist for a week. Some 10 years later the
researchers found that those who slept fewer than five hours or more
than 6.5 hours had a higher mortality.
Other experts caution against studies
showing ill effects from too much sleep. Illness may cause someone to
sleep or spend more time in bed, these experts say. And studies based on
people reporting their own sleep patterns may be inaccurate.
“The problem with these studies is that they
give you good information about association but not causation,” said
Timothy Morgenthaler, president of the American Academy of Sleep
Medicine, which represents sleep doctors and researchers, and a
professor of medicine at the Mayo Clinic Center for Sleep Medicine.
Dr. Morgenthaler advises patients to aim for
seven to eight hours of sleep a night and to evaluate how they feel.
Sleep needs also vary between individuals, largely due to cultural and
genetic differences, he said.
Getting the right amount of sleep is
important in being alert the next day, and several recent studies have
found an association between getting seven hours of sleep and optimal
cognitive performance.
A study in the journal Frontiers in Human Neuroscience last
year used data from users of the cognitive-training website Lumosity.
Researchers looked at the self-reported sleeping habits of about 160,000
users who took spatial-memory and matching tests and about 127,000
users who took an arithmetic test. They found that cognitive performance
increased as people got more sleep, reaching a peak at seven hours
before starting to decline.
After seven hours, “increasing sleep was not
any more beneficial,” said Murali Doraiswamy, a professor of psychiatry
at Duke University Medical Center in Durham, N.C., who co-authored the
study with scientists from Lumos Labs Inc., which owns Lumosity. He said
the study replicated earlier research, including a look at memory loss.
“If you think about all the causes of memory loss, sleep is probably
one of the most easily modifiable factors,” he said.
Most research has focused on the effects of
getting too little sleep, including cognitive and health declines and
weight gain. David Dinges, a sleep scientist at the University of
Pennsylvania’s Perelman School of Medicine who has studied sleep
deprivation, said repeatedly getting just 20 or 30 minutes less than the
minimum recommendation of seven hours can slow cognitive speed and
increase attention lapses.
Experts say people should be able to figure
out their optimal amount of sleep in a trial of three days to a week,
ideally while on vacation. Don’t use an alarm clock. Go to sleep when
you get tired. Avoid too much caffeine or alcohol. And stay off
electronic devices a couple of hours before going to bed. During the
trial, track your sleep with a diary or a device that records your
actual sleep time. If you feel refreshed and awake during the day,
you’ve probably discovered your optimal sleep time.
The new sleep guidelines will be drawn up by
a panel of experts being assembled by the American Academy of Sleep
Medicine, the Sleep Research Society, an organization for sleep
researchers, and the CDC. The recommendations are meant to reflect
evidence that has emerged from scientific studies and are expected to
take into account issues such as gender and age, says Dr. Morgenthaler,
the academy president.
Another group, the National Sleep
Foundation, a nonprofit research and advocacy group, also has assembled
an expert panel that expects to release updated recommendations for
sleep times in January.
These groups currently recommend seven to nine hours of nightly sleep for healthy adults. The National Heart, Lung and Blood Institute recommends seven to eight hours,
including the elderly. Most current guidelines say school-age children
should get at least 10 hours of sleep a night, and teenagers, nine to
10.
“I don’t think you can overdose on healthy
sleep. When you get enough sleep your body will wake you up,” said
Safwan Badr, chief of the division of pulmonary, critical care and sleep
medicine at Wayne State University School of Medicine in Detroit.
A study in the current issue of Journal of Clinical Sleep Medicine seemed
to confirm that. Five healthy adults were placed in what the
researchers called Stone Age-like conditions in Germany for more than
two months—without electricity, clocks or running water. Participants
fell asleep about two hours earlier and got on average 1.5 hours more
sleep than was estimated in their normal lives, the study said.
Their average amount of sleep per night: 7.2 hours.
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