Sleep on It
When counting sheep isn't enough
Elephants need only three to four hours of sleep a night, while mice sleep 14 hours. Humans are somewhere in the middle. But for many of us, sleep is never long enough or good enough.
About 30 percent of adults complain of problems sleeping, according to the National Institutes of Health. And the consequences go far beyond feeling tired the next day. People who average no more than six hours of sleep a night may have a higher risk of diabetes and heart disease, and may be more likely to eat more...and gain more weight. Here's what the latest research shows.
Getting a good night's sleep isn't easy.
"Women tend to sleep longer and sounder than men, although women complain more than men about their sleep," says sleep anthropologist Kristen Knutson of the University of Chicago.
"We don't know if that's because women are more willing to speak up, or if we're not measuring what's making women feel that their sleep is not refreshing."
In one study, "women slept about 7 hours 50 minutes while men slept 7 hours 30 minutes," says Marie-Pierre St-Onge, a sleep and obesity researcher at Columbia University in New York.1
Women also tend to get more slowwave sleep, the deep phase of sleep that's most restful and restorative.
Slow-wave sleep shrinks for both sexes as they age, starting for some in their 30s, says Jeanne Duffy, a neuroscientist at Brigham and Women's Hospital and Harvard Medical School in Boston.
"If you take a group of 60-year-olds, the women will have more slow-wave sleep than the men, though still less than younger women," she notes. "That may help explain why, as people get older, they're much more likely to complain about their sleep."
Typically, older adults can fall asleep and sleep for the first several hours of the night, says Duffy. But toward the later part of the night, they wake up and often can't get back to sleep or, if they do, can't remain asleep.
Researchers find that the number of very brief awakenings during the night—each typically lasts between five and 20 seconds—increases with age.
"Typical 25-year-olds may have only three or four of them," says Duffy, "while healthy 60-year-olds may have 25 or 30 throughout the night."
Despite all the bumps in the road to slumber, healthy sleep-deprived older people perform better the next day than sleep-deprived younger people, she notes.
"We're not sure if this means that older adults need less sleep than young adults. But even with less sleep, the older adults do better on many kinds of mental performance tests in the laboratory."
Still, the consequences of not getting enough restful sleep may be more serious than struggling to function the next day.
Diabetes & Heart Disease
"People who habitually sleep six or fewer hours a night are at increased risk of developing diabetes," says Knutson.
In a meta-analysis that pooled the results of 13 studies on more than 107,000 men and women who were followed for 4 to 32 years, those who reported sleeping six hours a night or less were 28 percent more likely to later be diagnosed with type 2 diabetes than those who slept seven or eight hours. The disease was 57 percent more likely among those who had difficulty falling asleep and 84 percent more likely among those who had trouble staying asleep.2
It's not just diabetes.
In a meta-analysis of 24 studies that followed more than 474,000 men and women for 7 to 25 years, those who reported sleeping less than six hours a night had a 48 percent greater risk of coronary heart disease than those who slept six to eight hours.3 Studies have also linked shorter sleep to high blood pressure in men and women under 60.4
But studies that find a higher risk of hypertension, heart disease, or diabetes in short sleepers can't prove cause and effect.
"Nonetheless, the associations are fairly consistent, strongly suggesting that poor sleep can lead to serious health problems," notes Knutson.
Insulin resistance could be the link. When researchers restrict young and middle-aged adults to about five hours of sleep a night for one to two weeks, they become more insulin resistant.5,6
If your cells are insulin resistant, they don't respond well to the hormone. And that can make your pancreas pump out more and more insulin. When it can't keep up, blood sugar rises and you have diabetes. Insulin resistance also increases the risk of heart disease.
"If lack of sleep leads to the development of insulin resistance, that might explain why it could raise the risk of diabetes and heart disease," says Knutson.
Do people who sleep less gain more weight? Among the 68,000 women in the Nurses' Health Study, those who reported sleeping five hours or less a night gained roughly 2½ more pounds over 16 years than those who reported sleeping seven hours. Those who said they slept six hours a night gained 1½ more pounds.7
And in a study that tracked the same nurses and some 70,000 other health professionals, those who slept less than six hours a night gained the most weight over 12 to 20 years.8
Those studies can't prove cause and effect either. Something else about short sleepers could explain their weight gain. But sleep-lab studies offer more evidence that sleeping less may lead to weighing more.
"There's substantial evidence from experiments in people that sleep deprivation leads to an increase in food intake," says Columbia University's St-Onge.
In her recent study, 30 people in their 30s and 40s ate an average of 300 more calories after being limited to about four hours of sleep a night for four nights than they did when they could sleep as long as they wanted to for four nights.1
And in an earlier study at the University of Chicago, men and women who weren't allowed to sleep for more than five hours a night for two weeks ate 220 more calories a day from snacks, particularly at night, than they did when they could sleep more than seven hours a night.9
Why might sleeping less make people eat more? "Studies find that depriving people of sleep raises their blood levels of ghrelin, a hormone that increases appetite, and lowers their blood levels of leptin, a hormone that inhibits appetite," says Knutson.10
What can you do to improve your sleep? Here's the latest on some remedies.
"There is a growing consensus that regular exercise can improve sleep," says Matthew Buman, a professor of exercise and wellness at Arizona State University.
In the largest study to date, Stanford University's Abby King and colleagues recruited 66 people aged 55 or older who exercised less than an hour a week and complained about their sleep.
"We chose people with typical mild to moderate sleep complaints who would love to sleep better but who didn't have a sleep disorder like chronic insomnia," says Buman, who helped analyze the data.
Thirty-six of the volunteers were randomly assigned to attend two onehour sessions a week of aerobic exercises, stretching, muscle strengthening, and balance exercises. They were also instructed to do 30 minutes of aerobic exercise at home at least three days a week.
The 30 volunteers in the control group were offered weekly classes on nutrition and other topics, but weren't told to exercise. After 12 months, the exercisers reported feeling more rested in the morning than the control group.11
"What's unique about this study is that it was the first to actually periodically measure the brain waves during sleep of people who were engaged in moderate-intensity exercise during the day," Buman notes.
The brain waves showed that the exercisers fell into a stable sleep four minutes sooner and awoke fewer times during the first third of the night than the control group. (Both groups slept about the same amount of time—six hours a night.)
The results were "modest and less dramatic than we originally expected," conceded the researchers, who were also disappointed that exercise didn't increase the time the volunteers spent in slow-wave sleep.
"A few short studies in younger adults have shown that on days they exercise they're likely to have more slow-wave sleep that night," Buman notes.
Exercise is most likely to help people whose sleep is the worst and who have been exercising the least, adds Buman.12
"Promotes restful sleeping," says GNC.
Helps you "get the tranquil rest you deserve," promises Nature's Bounty.
"Valerian does have sedative properties in animals," says sleep researcher Diana Taibi of the University of Washington. "But when you look at the studies in people, the effect on sleep, if any, is very small."
Most research on valerian "is poor quality," Taibi notes. One problem: "Although valerian is foul smelling, many of the studies didn't conceal the odor, so people knew if they were getting it," she says. "And since sleep disturbance is largely a psychologically conditioned problem, if someone takes something expecting it to help them sleep, it probably will."
In Taibi's trial, she and her colleagues gave 16 women in their 60s and 70s who suffered from insomnia either 300 milligrams of a valerian extract or a placebo 30 minutes before bedtime every night for two weeks. (The researchers stored the placebo next to the valerian, so it smelled just like the herb.) After a two-week break, the women switched to the other pills.
"When they were taking valerian, the women didn't fall asleep any faster, sleep any longer, or report any better sleep quality than when they were taking the placebo," says Taibi. In fact, the women were awake for an average of 11 minutes more the nights they were taking valerian.13
(The valerian used in the study was made by Pharmavite, which claims that its NatureMade brand of valerian is "supported by clinical trials.")
"Our results are consistent with most of the 29 previous studies in people with insomnia," says Taibi. What's more, she adds, none of the most recent studies, which were also the most carefully controlled, found any significant effect of valerian on sleep.14
However, Taibi notes, none of the studies looked at valerian tinctures, which are solutions of valerian extracts in alcohol. "The effects of tinctures could be entirely different," she says. "But since it has never been tested, we don't know."
"Provides relief for occasional sleeplessness," says Natrol about its melatonin pills. "For restful & peaceful sleep," claims "instant acting" Sleep Soundly liquid melatonin.
"Melatonin is a hormone produced in the brain at night that precedes the onset of sleep but doesn't necessarily cause sleep," says Harvard's Jeanne Duffy.
In 2004, the U.S. Agency for Healthcare Research & Quality (AHRQ) concluded that melatonin isn't effective in treating most "primary" or "secondary" sleep disorders. ("Primary" means that doctors can find no cause of the insomnia. "Secondary" disorders are caused by other conditions— depression or sleep apnea, for example.)
But the AHRQ found that travelers with jet lag or night workers who took melatonin (usually 5 or 6 milligrams) slept an average of 18 minutes more than similar people who took a placebo. The hormone didn't help them fall asleep any faster or sleep any better, though.15
The AHRQ also found that melatonin might help with an uncommon condition called "delayed sleep phase syndrome," in which patients typically fall asleep hours after midnight and have difficulty waking up in the morning because their "internal clock" is off.
In two studies, melatonin helped patients with delayed sleep phase syndrome fall asleep an average of about 40 minutes earlier than usual.16,17 "Melatonin can help pull their sleep timing back somewhat so they can go to sleep earlier and get up earlier," says Taibi.
- Kava. "Although scientific studies provide some evidence that kava may be beneficial for the management of anxiety," notes the National Institutes of Health's National Center for Complementary and Alternative Medicine, it "is not a proven therapy for other uses." What's more, the World Health Organization has reported more than 60 cases of possible liver toxicity in kava users. The WHO warns that kava shouldn't be used with drugs that prevent blood clots, psychotic episodes, or anxiety.
- Yoga. "Yoga might help with sleep by promoting relaxation," says Taibi. However, evidence from controlled studies is elusive. In the only trial in the U.S. and Canada in adults, women reported no better quality of sleep after participating in a low-intensity yoga program for four months.18
- Warm baths. "Body temperature typically is high until right before you go to bed," notes Duffy. "Then there's a rapid decline." The lowest temperature is reached just before morning. "The drop in body temperature is one of the physiological triggers for sleep," says Taibi. When you take a warm bath, the dissipation of heat afterwards can set off that trigger, she explains. In two studies, when 23 women in their 60s and 70s with insomnia took a hot bath (105° F) 90 minutes before bedtime, they awoke less during the night than when they took a lukewarm bath (100° F) or no bath at all. The women also reported that their sleep was deeper and more restful.19,20
"People don't realize how much caffeine can interfere with sleep," says Thomas Roth, chief of sleep medicine at Henry Ford Hospital in Detroit. "They think that if the caffeine is out of their system, they're okay. But they may not be."
Caffeine affects sleep by interfering with adenosine, a compound found in every cell in the body. "In the brain, it pushes you to sleep," Roth explains. "If you inject adenosine into the brain of an animal, it will go to sleep."
While you're awake during the day, your brain is building up its levels of adenosine, says Roth. The adenosine is dissipated while you sleep, unless you don't sleep long enough to get rid of it all. That's where caffeine comes in.
Caffeine binds to adenosine receptors in the brain. That prevents the adenosine from entering nerve cells, so it can't make you drowsy.
While most people know that caffeine can disrupt sleep if it's consumed in the evening, "what isn't widely known is that caffeine taken earlier in the day can disrupt sleep later that night," says Roth.
When nine healthy young men who regularly drank one or two caffeinated beverages a day consumed 200 milligrams of caffeine at 7 a.m., their sleep was affected 16 hours later when they went to bed at 11 p.m., even though they had no more caffeine during the rest of the day and the level in their blood was approaching zero. (A 16 oz. grande brewed coffee at Starbucks has 330 mg of caffeine.)
It took them 11 more minutes to fall into deep sleep, and their total sleep time averaged 10 minutes less than on a night when they consumed a placebo instead of caffeine in the morning. 21 "Ten minutes isn't a big deal for a single day," says Roth. "But it is a big deal as a nightly issue."
"If you occasionally drink alcohol just before bedtime, it will put you to sleep more quickly for the first couple of hours and increase your slow-wave sleep, but then it will spoil your sleep during the latter part of the night," says Roth.
"After about two hours—the time depends on how much you've had— your body starts to clear the alcohol from your system," he explains. "You begin getting fragmented sleep, which is waking up briefly and repeatedly, and then disrupted sleep, which is awakening from dreams and returning to sleep with difficulty."
If you regularly drink alcohol to fall asleep, Roth adds, its sleep-inducing effect eventually wears off, but you'll still have fragmented and disrupted sleep.
Women and older people are especially vulnerable because the same dose produces higher levels of alcohol in their blood and their brain than it does in men and younger people. Another hazard: older people who drink before going to bed may be unsteady if they have to get up during the night to go to the bathroom.
The Bottom Line
- Sleeping six hours a night or less may raise the risk of diabetes, heart disease, obesity, and insulin resistance.
- Aerobic exercise may improve sleep.
- Melatonin may help with jet lag, night work, or delayed sleep phase syndrome.
- Valerian doesn't help most people sleep longer or better.
- Caffeine and alcohol may disturb sleep.
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2 Diabetes Care 33: 414, 2010.
3 Eur. Heart J. 32: 1484, 2011.
4 Blood Press. 21: 45, 2012.
5 J. Clin. Endocrinol. Metab. 94: 3242, 2009.
6 Diabetes 59: 2126, 2010.
7 Am. J. Epidemiol. 164: 947, 2006.
8 N. Engl. J. Med. 364: 2392, 2011.
9 Am. J. Clin. Nutr. 89: 126, 2009.
10 Ann. Intern. Med. 153: 435, 2010.
11 J. Gerontol. A Biol. Sci. Med. Sci. 63: 997, 2008.
12 Health Psychol. 30: 579, 2011.
13 Sleep Med. 10: 319, 2009.
14 Sleep Med. Rev. 11: 209, 2007.
15 AHRQ Publication No. 05-E002-2, 2004.
16 Lancet 337: 1121, 1991.
17 Psychosom. Med. 63: 40, 2001.
18 Menopause 14: 535, 2007.
19 J. Geriatr. Psychiatry Neurol. 9: 83, 1996.
20 Sleep 22: 891, 1999.
21 Brain Res. 675: 67, 1995.
Contact Jeff Cronin (jcronin[at]cspinet.org) or Ariana Stone (astone[at]cspinet.org).