Sex Sleep Eat Drink Dream (26 page)

I might turn to a nightcap for help drifting off, but the practice is not recommended. Though a drink before bed may initially make one feel drowsy, once the alcohol has been processed by the body, the resulting compounds have a stimulating effect, disrupting slumber later in the night. Researchers recently glimpsed why this might be so. Alcohol affects the thalamus, a region of the brain integral to sleep-wake rhythms and to the spindle waves that occur during stage 2 sleep. So sensitive is the thalamus, researchers say, that just a drink or two will make for lighter sleep in the middle of the night, or even full wakefulness.

I know I'll eventually drop off. I'm not like the incurable insomniac for whom night is no downward slope to certain oblivion, but rather a flat and despairing palm of wakefulness. Still, I have too many demands the next day to lose even an hour's rest.

Losing sleep didn't always feel so—well—so
punishing.
Once, when I was asleep in a lean-to hut in the mountains of New Hampshire, some night animal rustled or hooted me awake. I slithered to the edge of the wooden platform and lay there in my sleeping bag, watching a crescent moon slowly slide across the sky and then set over a pine-edged slope. The night was all stars and dew and strange perfumes, and the hours passed by lightly, with faint shifts of temperature and luminosity. I felt energetic, awed, happy to stay awake through the night to witness its transit.

But I was young then. Now I'm a working mother jealous of my slumber. So what do I do? Fret, brood, lose sleep. And what of it?

Sleep is sore labor's bath, nature's soft nurse, the balm of hurt minds. It is Nabokov's moronic fraternity or Coleridge's gentle thing, belov'd from pole to pole. The number of metaphorical descriptions of what sleep
is
is nearly matched by the number of theories about what it
does.
In the past few decades we have made good progress teasing apart the physiology and neural architecture of sleep, but the question of its purpose remains a biological dilemma of the first order. What could possibly be the advantage of so complicated and dangerous an undertaking as shutting down our sensory systems, paralyzing our muscles, putting ourselves at risk for a third of our hours? Wouldn't it be far better to be ever ready, up and running?

"If sleep does not serve an absolutely vital function," Allan Rechtschaffen once noted, "then it is the biggest mistake the evolutionary process has ever made."

This vital function, however, has proved devilishly elusive. One common technique to reveal the job of a bodily organ or behavior is to take it away. Rechtschaffen and his colleagues at the University of Chicago conducted a famous series of experiments showing that rats deprived of sleep eat more than usual but still lose weight and double their energy expenditure. They lose control of their body temperature and develop sores on their paws and tails that don't heal. After about two and a half weeks, they die—faster than if totally deprived of food.

For obvious reasons, no such experiments have been conducted on humans. But in 1965, a high school senior named Randy Gardner deprived himself of sleep for 264 hours to break the world record as part of a project for the San Diego Science Fair. After the allotted eleven days of continuous wakefulness, Gardner suffered no psychosis and no serious medical problems, but he did show deficits in concentration, motivation, and perception—as did William Dement, who observed him. Dement began spending nights at Gardner's house on the second day of the experiment to make sure the young man stayed awake and to monitor his physical and mental health. On the fifth day of his own wakefulness, Dement drove his car the wrong way up a one-way street and almost collided with a police car.

Such cases of sleep deprivation are extreme, of course. "There's another long-term, massive experiment in minor sleep debt going on in contemporary culture," says Charles Czeisler. A 2005 poll taken by the National Sleep Foundation found that about 40 percent of Americans get less than seven hours of sleep a night during the work week. That's an hour or two less than people got fifty years ago. Moreover, one in six people reported sleeping less than six hours a night—a substantial curtailment of sleep that may have serious consequences.

Consider the case of my friend Harri, a vibrant woman in her early fifties who teaches reading. One spring morning, Harri woke up with profound amnesia. She couldn't recall anything she had done or said the previous evening. She remembered making dinner and sitting down with her family to eat, but the span of hours after dinner was a blank.

Harri doesn't drink or smoke or take any drugs and considers herself in good health. The memory lapse spooked her a little, but she wrote it off to stress. Then it happened again; then twice more in one week. One evening, when her teenage son called from college, she spoke with him at length, but the following morning she had no recollection of the conversation. Her son told her later that she had been so unresponsive on the phone that he had yelled, "
Get Dad!
"

Finally, Harri consulted a neurologist. "I just wanted to know that it wasn't a brain tumor," she said. "I thought I could deal with just about anything else." At first the doctor suspected epilepsy, but a battery of EEGs and other tests proved normal. Then she inquired about Harris sleep habits. Ever since Harri could remember, she had slept only five hours a night. "It's not that I wasn't tired," she said. "I just felt I should squeeze as much as I could into the day by stealing an extra two or three hours to work."

I can understand the temptation. By staying up just one more hour each day for, say, seventy years, one could add to life 25,550 hours of reading time. But cheating sleep comes at a price. The result of Harri's cumulative sleep deprivation, the doctor told her, was a pathological sleepwalking state. After dinner, her brain dozed while her body continued to go through the motions of the evening.

Following the prescription was simple: Get at least seven hours of sleep. This Harri does now, religiously, and her amnesic episodes have disappeared.

"Overmuch" sleep "dulls the spirits," wrote Robert Burton in his
Anatomy of Melancholy,
"fills the head full of gross humours; causeth distillations, rheums, great store of excrements in the brain, and all other parts." As recently as a decade ago, eminent researchers in the sleep field were actively engaged in convincing people that they need not sleep long to sleep well. The idea was that only a "core" of four or five hours of sleep was necessary; the remaining three or four hours we spent in bed was optional, a luxury or hedge against future over-whelming physiological demands, but not required for optimal brain function. The extra hours of sleep were like the excess pounds of body fat we carry as anachronistic protection against periodic bouts of famine; in our current mode of living, we just don't need them anymore.

Of late, scientists have unequivocally overturned this belief. Though just how much sleep is best is still debated, evidence is mounting to suggest that for most of us, between seven and eight hours is optimal; less than six is simply not enough. David Dinges and his colleagues at the University of Pennsylvania found that people who slept less than six hours a night for two weeks took a dive in cognitive performance equal to two nights of total sleep deprivation. Though the sleep-restricted subjects reported feeling only slightly sleepy, they did poorly on nearly all tests of alertness, attention, coordination, and cognitive tasks. Those who slept only four hours a night for the same two-week period had total lapses like my friend Harris, when they simply failed to respond to a stimulus.

Other studies have reported that in terms of sedative effects and performance impairment, losing two hours of sleep out of a regular eight is tantamount to drinking two or three beers; losing four hours is like drinking five beers; and losing a whole night's sleep is like downing ten.

Sometimes we can compensate for the deprivation. Feelings of sleepiness may be offset by the alerting effects of our circadian clock and the stimulus of excitement, interest, or stress. And some studies suggest that sleep loss can actually increase activity in parts of the cortex not normally involved in a given task, suggesting that the brain may call in reinforcements to counter the dulling effects of sleep deprivation.

But there are limits. "With one night of short sleep, some people don't feel much impact," says Czeisler. "But everyone suffers after a week or two because the effects are cumulative. One week of restricted sleep builds a level of impairment equivalent to 24 hours of consecutive wakefulness. Two weeks is like 48 hours."

With prolonged sleeplessness, people often fall quickly into microsleeps, those sleep episodes of three to ten seconds that push through wakefulness. When you're driving down the highway at sixty miles per hour, that's enough time to veer off track hundreds of feet—say, across the median strip. The National Highway Traffic Safety Administration (NHTSA) estimates that drowsiness increases a driver's risk of a crash or near crash by at least a factor of four and that drowsy driving is responsible each year for at least 100,000 accidents and 1,500 fatalities.

Drowsiness is considered a major cause of accidents in virtually all forms of transport, surpassing alcohol and drugs. As William Dement points out, most people don't know that sleep deprivation, not alcohol, was a key factor in causing the
Exxon Valdez
to run aground in 1989, spilling millions of gallons of crude oil. The shipmate in control of the tanker at the time was operating on only six hours' sleep over two full days—not enough to stay alert, according to the National Transportation Safety Board. This was also the case in the tragedy of 2002 in Webbers Falls, Oklahoma, when a barge struck an interstate highway bridge, killing fourteen people, and in the explosion of the space shuttle
Challenger.
The night before the
Challenger
launch,
NASA
managers had gotten less than two hours of sleep. The report on the disaster suggested that sleep deprivation may have impaired their judgment about launching the rocket despite temperatures too cold to allow the O-rings to function properly.

How could the experts have been so wrong in the past about the devastating cognitive effects of accumulated sleep debt? In part, because scientists relied on subjects' self-reported feelings of sleepiness rather than on objective performance tests, says Czeisler. We are poor judges of our own sleepiness and its impact on our functioning. We tend not to recognize the signals of serious fatigue or realize the effect it has on how we listen, read, calculate, talk, operate machines, or drive. "And most of us," adds Czeisler, "have forgotten what it really feels like to be awake."

The mischief done by shortchanging sleep goes well beyond the workings of the mind. Eve Van Cauter, a sleep researcher at the University of Chicago, has found that restricting sleep to four or fewer hours for successive nights results in widespread changes in the body, including some that cause illness and mimic the hallmarks of aging.

To parse the popular belief that losing sleep increases one's chance of getting sick, Van Cauter examined the effect of sleep restriction on the body's immune response to vaccination. She and her team administered flu vaccines to a group of twenty-five volunteers who had slept only four hours a night for six nights. Ten days after the vaccination, their antibody response was less than half that of normal sleepers.

Van Cauter also found that sleep loss impairs the body's ability to perform basic metabolic tasks, such as regulating blood sugar and hormones, creating changes that closely resemble those of aging. After several nights of sleep restriction, a group of eleven lean and healthy young men showed signs of trouble processing blood sugar, causing a condition that looked like early diabetes. The ability of their insulin to respond to glucose was reduced by a third, and they took 40 percent longer than normal to regulate their blood sugar after a high-carbohydrate meal. The subjects also showed high levels of Cortisol during the evening hours, when the hormone is supposed to ebb. This late-day spike in Cortisol— a risk factor for hypertension—is typical of much older people. In some subjects, the severe sleep restriction had the effect of making the body of an eighteen-year-old look like that of a much older man.

Most of us know from experience that when we're tired from too little sleep, we tend to eat more. Van Cauter and her team have discovered an explanation: Sleep restriction reduces the body's supply of leptin, the hormone that signals satiety and regulates energy balance. She and her team have reported that subjects whose sleep was restricted to four hours a night had 18 percent less leptin in their blood and 28 percent more of the "hunger hormone" ghrelin than those sleeping seven or eight hours a night. They also felt hungrier and had more appetite for calorie-dense carbohydrates such as cake and bread. The body seems to respond to a loss of a few hours' sleep in the same way it responds to a deficit of about one thousand calories—by cueing its systems to slow metabolism, deposit more fat, and step up appetite, particularly for high-calorie foods.

In fact, Van Cauter suspects that the epidemic of insufficient sleep in our society may be responsible for the epidemic of obesity. Indeed, in 2005 researchers showed that obesity is tightly correlated with sleep time. The survey of 9,500 people from across the United States, aged thirty-two to forty-nine, revealed that those who reported sleeping five hours a night were 60 percent more likely to be obese than their counterparts who slept seven hours or more.

A twist to this tale comes from a 2006 report on the sleep habits and weight gain of 68,000 women over a sixteen-year period. Like the women in the earlier study, the subjects who slept five hours or less were more likely to gain weight over time than those who slept seven hours—but not because they ate more or exercised less. In fact, on average, the short-sleepers in the study consumed fewer calories and had roughly the same level of physical activity. The culprit, instead, could be a lower metabolic rate or reduced nonexercise activity thermogenesis—the
NEAT
movements we saw earlier, such as fidgeting—that may come with sleep restriction.