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 body’s secretion of some hormones. The changes promote appetite, reduce the sensation of feeling full after a meal, and alter the body’s response to sugar intake—changes 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 sleep—lights, 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 Night’s Sleep, Published By McGraw-Hill, and is the Chief Medical Officer for Sleep Healthcenters in Boston.