While researchers probe sleep's functions, sleep itself is becoming a lost art.
Not long ago, a psychiatrist in private practice telephoned associate professor of psychiatry Robert Stickgold, a cognitive neuroscientist specializing in sleep research. He asked whether Stickgold knew of any reason not to prescribe modafinil, a new wakefulness-promoting drug, to a Harvard undergraduate facing a lot of academic work in exam period.
The question resonated on several levels. Used as an aid to prolonged study, modafinil is tantamount to a “performance-enhancing” drug—one of those controversial, and often illegal, boosters used by some athletes. In contrast to wakefulness-producing stimulants like amphetamines, modafinil (medically indicated for narcolepsy and tiredness secondary to multiple sclerosis and depression) does not seem to impair judgment or produce jitters. “There’s no buzz, no crash, and it’s not clear that the body tries to make up the lost sleep,” reports Stickgold. “That said, all sleeping medications more or less derange your normal sleep patterns. They do not produce normal sleep.” Even so, the U.S. military is sinking millions of dollars into research on modafinil, trying to see if they can keep soldiers awake and on duty—in Iraq, for example—for 80 out of 88 hours: two 40-hour shifts separated by eight hours of sleep.
“No—no reason at all not to,” Stickgold told the psychiatrist. “Not unless you think sleep does something.”
When people make the unlikely claim that they get by on four hours of sleep per night, Stickgold often asks if they worry about what they are losing. “You get a blank look,” he says. “They think that sleep is wasted time.” But sleep is not merely “down time” between episodes of being alive. Within an evolutionary framework, the simple fact that we spend about a third of our lives asleep suggests that sleep is more than a necessary evil. Much transpires while we are asleep, and the question is no longer whether sleep does something, but exactly what it does. Lack of sleep may be related to obesity, diabetes, immune-system dysfunction, and many illnesses, as well as to safety issues such as car accidents and medical errors, plus impaired job performance and productivity in many other activities.
Although the modern era of sleep research started in the 1950s with the discovery of REM (Rapid Eye Movement) sleep, the field remained, well, somnolent until recently. Even 20 years ago, “The dominant paradigm in sleep research was that ‘Sleep cures sleepiness,’” says Stickgold. Since then, researchers have developed a far more complex picture of what happens while we snooze. The annual meetings in sleep medicine, which only this year became a recognized medical specialty, now draw 5,000 participants. Harvard has long been a leader in the area. The Medical School’s Division of Sleep Medicine, founded in 1997 and chaired by Baldino professor of sleep medicine Charles Czeisler, has 61 faculty affiliates. The division aims to foster collaborative research into sleep, sleep disorders, and circadian biology, to educate physicians and the lay public, to influence public policy, and to set new standards of clinical practice, aiming, as its website (
www.hms.harvard.edu/sleep) declares, to create “a model program in sleep and circadian biology.”
A Culture of “Sleep Bulimia”
Imagine going on a camping trip without flashlights or lanterns. As the sun sets at the end of the day, daylight gradually gives way to darkness, and once the campfire burns down, you will probably go to sleep. At sunrise, there’s a similar gradient in reverse; from the beginning of time, human beings have been entrained to these cycles of light and dark.
Homo sapiens is not a nocturnal animal; we don’t have good night vision and are not especially effective in darkness. Yet in an instant on the evolutionary time scale, Edison’s invention of the light bulb, and his opening of the first round-the-clock power plant on Pearl Street in Manhattan in 1882, shifted our time-and-light environment in the nocturnal direction. At the snap of a switch, a whole range of nighttime activity opened up, and today we live in a 24-hour world that is always available for work or play. Television and telephones never shut down; the Internet allows you to shop, gamble, work, or flirt at 3 a.m.; businesses stay open ever-longer hours; tens of millions of travelers cross multiple time zones each year, worldwide; and with the growth of global commerce and communication, Wall Street traders may need to rise early or stay up late to keep abreast of developments on Japan’s Nikkei exchange or at the Deutsche Bundesbank.
Consequently most of us now sleep less than people did a century ago, or even 50 years ago. The National Sleep Foundation’s 2005 poll showed adult Americans averaging 6.8 hours of sleep on weeknights—more than an hour less than they need, Czeisler says. Not only how much sleep, but when people sleep has changed. In the United States, six to eight million shift workers toil regularly at night, disrupting sleep patterns in ways that are not necessarily amenable to adaptation. Many people get only five hours per night during the week and then try to catch up by logging nine hours nightly on weekends. “You can make up for acute sleep deprivation,” says David P. White, McGinness professor of sleep medicine and director of the sleep disorders program at Brigham and Women’s Hospital. “But we don’t know what happens when people are chronically sleep-deprived over years.”
“We are living in the middle of history’s greatest experiment in sleep deprivation and we are all a part of that experiment,” says Stickgold. “It’s not inconceivable to me that we will discover that there are major social, economic, and health consequences to that experiment. Sleep deprivation doesn’t have any good side effects.”
All animals sleep. Fish that need to keep swimming to breathe sleep with half their brains while the other half keeps them moving. It is uncertain whether fruit flies actually sleep (“We can’t put electrodes in their brains,” says White), but they seem at least to rest, because for extended periods they do not move. When researchers stopped fruit flies from resting by swatting at them, the flies took even longer rest periods. When lab technicians added caffeine to the water that the flies drank, they stayed active longer—and also rested longer after the drug wore off, evidence that the caffeine had disrupted their resting patterns.
Sleeping well helps keep you alive longer. Among humans, death from all causes is lowest among adults who get seven to eight hours of sleep nightly, and significantly higher among those who sleep less than seven or more than nine hours. (“Those who sleep more than nine hours have something wrong with them that may be causing the heavy sleep, and leads to their demise,” White notes. “It is not the sleep itself that is harmful.”)
Sleep is essential to normal biological function. “The immune system doesn’t work well if we don’t sleep,” says White. “Most think sleep serves some neurological process to maintain homeostasis in the brain.” Rats totally deprived of sleep die in 17 to 20 days: their hair starts falling out, and they become hypermetabolic, burning lots of calories while just standing still.
There once was a fair amount of research on total sleep deprivation, like that which killed the rats. Doctors would keep humans awake for 48, 72, or even 96 hours, and watch their performance deteriorate while their mental states devolved into psychosis. For several reasons, such studies rarely happen any more (“Why study something that doesn’t exist?” asks White) and researchers now concentrate on sleep restriction studies.
In this context, it is important to distinguish between acute and chronic sleep deprivation. Someone who misses an entire night of sleep but then gets adequate sleep on the following three days “will recover most of his or her normal ability to function, ” Czeisler says. “But someone restricted to only five hours of nightly sleep for weeks builds up a cumulative sleep deficit. In the first place, their performance will be as impaired as if they had been up all night. Secondly, it will take two to three weeks of extra nightly sleep before they return to baseline performance. Chronic sleep deprivation’s impact takes much longer to build up, and it also takes much longer to recover.” The body is eager to restore the balance; Harvard undergraduates, a high-achieving, sleep-deprived population, frequently go home for Christmas vacation and pretty much sleep for the first week. Stickgold notes that “When you live on four hours a night, you forget what it’s like to really be awake.”
Sleep researcher Eve van Cauter at the University of Chicago exposed sleep-deprived students (allowed only four hours per night for six nights) to flu vaccine; their immune systems produced only half the normal number of antibodies in response to the viral challenge. Levels of cortisol (a hormone associated with stress) rose, and the sympathetic nervous system became active, raising heart rates and blood pressure. The subjects also showed insulin resistance, a pre-diabetic condition that affects glucose tolerance and produces weight gain. “[When] restricted to four hours [of sleep] a night, within a couple of weeks, you could make an 18-year-old look like a 60-year-old in terms of their ability to metabolize glucose,” Czeisler notes. “The sleep-deprived metabolic syndrome might increase carbohydrate cravings and the craving for junk food.”
Van Cauter also showed that sleep-deprived subjects had reduced levels of leptin, a molecule secreted by fat cells that acts in the brain to inhibit appetite. “During nights of sleep deprivation, you feel that your eating goes wacky,” says Stickgold. “Up at 2 a.m., working on a paper, a steak or pasta is not very attractive. You’ll grab the candy bar instead. It probably has to do with the glucose regulation going off. It could be that a good chunk of our epidemic of obesity is actually an epidemic of sleep deprivation.”
Furthermore, “Many children in our society don’t get adequate amounts of sleep,” Czeisler says. “Contrary to what one might expect, it’s common to see irritability and hyperactivity in sleep-deprived children. Is it really surprising that we treat them with wake-promoting drugs like Ritalin?” Schools and athletic programs press children to stay awake longer, and some children may be chronically sleep-deprived. Czeisler once took his daughter to a swim-team practice that ran from eight to nine o’clock at night, and told the coaches that this was too late an hour for children. “They looked at me like I was from another planet,” he recalls. “They said, ‘This is when we can get the pool.’”
Stickgold compares sleep deprivation to eating disorders. “Twenty years ago, bulimics probably thought they had the best of all worlds,” he says. “They could eat all they wanted and never gain weight. Now we know that they were and are doing major damage to their bodies and suffering major psychological damage. We live in a world of sleep bulimia, where we binge on weekends and purge during the week.”
