Sex Sleep Eat Drink Dream (13 page)

I stepped into the shoes of the caretaking mother for three hours a day a few times a week. My mother lived that role twenty-four hours a day for well over a decade. The effort of doing so—of feeding, bathing, ministering to my handicapped sister while caring for a family of seven—stole virtually all of her stamina.

Even those of us who aren't saddled with this sort of extreme caretaking job are fatigued from working long hours—longer than those worked a generation ago. Since then, Americans have managed to squeeze the equivalent of at least another week's worth of labor into the work year. The problem is this: When one packs life with unrelenting activity and little chance to relax and refuel, the body begins to feel run-down. Some evolutionary biologists view this kind of fatigue as the body's smoke detector or warning signal, its way of telling us to slow down to prevent the physical and mental harm of overexertion.

A deep seasonal rhythm largely ignored by modern society may also contribute to fatigue. Lethargy is one of the chief symptoms of seasonal affective disorder
(SAD),
a reaction to the waning sunlight of winter. A Norwegian friend of mine once told me about a word used to describe the season in her country,
morketiden,
or murky time, when a drape of darkness falls not just on the winter landscape but on the inner world of the soul. Underlying
SAD
is the persistent rhythm of our circadian pacemaker, which still has the capacity to detect and react to seasonal changes in day length, says Russell Foster, a circadian biologist at the Imperial College Faculty of Medicine in London. In response to the shorter hours of daylight, the brain secretes melatonin for a longer period during the longer night hours, putting the body in "night mode." It also reduces its production of serotonin, a neurotransmitter involved in regulating mood. But in modern society we don't slow down to accommodate our shifting seasonal chemistry; in winter, we continue to work long hours and stay up late at night, and our bodies suffer. For a small percentage of people—greater in countries at high latitudes—the wintertime decrease in daylight and overproduction of melatonin may cause a full-blown case of
SAD:
weight gain, reduced physical activity, and overwhelming fatigue. Daily exposure to a light source for prescribed periods can ease symptoms of the disorder.

Despite mounds of research, science is still struggling to understand commonplace fatigue. It ranks as one of the most frequent health complaints in this country, accounting for up to fifteen million doctor visits a year. But despite its pervasiveness, it is not an easy state to quantify, or even define.

Fatigue is not just feeling sleepy. You can be sleepy without being fatigued, and fatigued without being sleepy. It can be physical—the sensation of weariness in the body; or emotional—feeling unmotivated and bored; or mental—lacking concentration or sharpness. It can be diminished by encouragement and motivational cues (researchers have found that the perception of fatigue can be manipulated during a physically challenging activity simply by providing feedback on performance), or by financial incentives (one study showed that people promised a $5 reward were able to hang from a horizontal bar for almost twice as long as control subjects or subjects who were merely encouraged by the experimenter), or by the suggestion that the effort one is expending is less than it was before—even if it's not.

Fatigue can be so severe that it's incapacitating and yet, in fear or excitement, quickly forgotten. It may arise from grief, disappointment, physical illness, pain, the malignant and exhausting gloom of depression, lack of sleep, or relentless labor. So stymied are some scientists by the elusive quality of the concept that they argue it should be dumped altogether.

I hold with my mother's definition: Fatigue is the enemy.

In any case, exhaustion from a half day of wakefulness is not the foe we face each afternoon. After all, our energy often picks up following the midday lull. Nor is the culprit an ebb in body temperature, as is the case with parallel dips in the very early morning hours. What is the offender then? Is the post-iunch slump a consequence of that turkey sandwich and corn salad devoured earlier in the warm sun of the veranda?

Some evidence suggests that a big meal may contribute to the lassitude. "Gastric stretch" is thought to have some sleep-inducing influence (just as the absence of food may have an arousing influence). So, too, the movement of food from the stomach to the duodenum may exacerbate drowsiness. In cats, the mere act of gently stimulating the lining of the small intestine brings about acute sleepiness. Insulin, too, may play a part. Immediately after a feast, the body often experiences a temporary boost in energy from the rise in glucose, or blood sugar. But then follows a surge of insulin, the hormone that transports sugar to cells. In an effort to store the excess of sugar, insulin may extract too much of it from the blood, leaving little free for immediate energy. A big meal rich in fat may worsen the nosedive in alertness and performance, say researchers from the University of Sheffield, possibly because fat triggers the release of CCK, that hormone of satiety, which has been shown to cause sedation in humans and other animals.

However, research shows that the dip occurs whether or not you eat lunch. When scientists compared midafternoon sleepiness in young men who ate a heavy lunch, a light one, or no lunch at all, they found that 92 percent of the eaters napped afterward for a solid ninety minutes, regardless of the size of their meal; the fasters slept too, though only for thirty minutes. Lunch may aggravate or prolong the doldrums, say the researchers, but it doesn't induce them.

No one is sure what precipitates the afternoon trough. The work of Carskadon and others suggests that it may arise from a glitch in the timing of two opposing processes at work in our lives. First there's the homeostatic sleep mechanism, which acts like a sleep thermostat, keeping track of how long we've been awake. The need-to-sleep tab starts running as soon as we get up in the morning and tallies our sleep debt over the hours. As it builds, this homeostatic force exerts more and more pressure to discharge the debt, and we grow sleepier over the course of a day.

Every hour and a half to two hours, we feel an especially strong wave of sleepiness. Peretz Lavie confirmed this when he tested people's propensity for sleep by asking them to try to fall asleep every 20 minutes over a 24-hour period, a total of 72 attempts. Lavie found that a "sleep gate"—a window of "sleepability" when we may drift off relatively easily—swings open roughly every 90 to 120 minutes. The cycle is most pronounced at night (when shift workers may suffer alternating bouts of clarity and intense sleepiness), but it's also at work during the day. This pattern of sleep vulnerability occurs whether or not you have slept well the night before.

What keeps us awake and alert through these periodic swings of the sleep gate is the other process shaping our days: the circadian alerting mechanism, controlled by our central pacemaker, the SCN. Dale Edgar of the Stanford University School of Medicine verified the location of the alerting mechanism in a study of squirrel monkeys. The species has human-like sleep-wake patterns—staying awake for about sixteen hours, then sleeping solidly for eight: When Edgar destroyed the monkeys' SCN, they fell asleep again and again all day long.

Over the course of a waking day, this circadian alerting system beats a different rhythm from the sleep thermostat, says Carskadon. The alertness signal is lowest in the very early morning, say around 3
A.M.,
when body temperature is at its nadir. As the day goes on, the wakefulness signal gets stronger and stronger, counteracting the growing homeostatic pressure for sleep. A potent wave of alertness sweeps over us a few hours after waking, which may account for our late-morning mental agility. By early evening, the alerting signal is so powerful that it creates a "wake zone" a few hours before it begins its downward slide into circadian night.

Throughout the day and night, then, your body is subject to the push-pull of these two processes. For most of the daylight hours, the alerting mechanism overrides the homeostatic drive for sleep and rouses our bodies into a bright-eyed state. But around midday, says Carskadon, "sleep pressure accumulates before clock-dependent alerting achieves adequate strength to offset sleepiness"; we're overcome with a surge of drowsiness, and the sleep gates open wide.

Just how severely you suffer the slings of this afternoon slump may depend on your chronotype, notes Carskadon. "Evening types tend to experience waves of greater amplitude," she explains, "with higher peaks of alertness and lower troughs of drowsiness, as well as a mountain of alertness in the evening." Morning types, on the other hand, "have a relatively flat alertness curve during the day, which then falls off rather dramatically in the evening."

But most people experience some midday dip or trough, says Carskadon. For those on the road, these are dangerous hours. Studies of fatigue-related accidents in Israel, Texas, and New York show that single-vehicle accidents (driving off the road, for example) are most common not only in the wee hours of the morning, between 1 and 4
A.M.,
but also in midafternoon, between 1 and 4
P.M.
This double peak also appears in the temporal distribution of public-bus accidents in the Netherlands and railway accidents in Germany. In fact, studies from all over the world show an afternoon spike in sleep-related driving accidents. At around 4
P.M.,
drivers are three times more likely to fall asleep at the wheel than they are at 10
A.M.
or 7
P.M.
In a world where human error may cause accidents involving large numbers of people, these drops in efficiency can have a catastrophic impact.

Those of us listening to the sleep lectures in our comfy auditorium seats wouldn't have felt logy if we had been outside in the wild coastal weather of Amelia Island. The gusty breeze and roiling waves of an impending storm would have boosted heart rate, dilated pupils, slammed shut those sleep gates. But ordinarily we don't have the advantage of hurricane-force winds to keep us perky. So how else to rescue alertness?

There are two ways to go. Try to override the rhythm, bear down on your work or your driving or whatever task is at hand, and ignore the open sleep door at your own peril. Or briefly go through it: pull over at a rest stop on the highway or put your head on your desk or, if you're lucky enough to have a couch, stretch out and snatch forty winks.

"Very bad habit! Very bad habit!" Captain Giles says in Joseph Conrad's
The Shadow-Line,
chiding himself as he retires for an afternoon snooze.

Catnap, siesta, forty winks, rest involving sleep but not pajamas—a nap is technically defined as a daytime sleep episode of more than five minutes and less than four hours. Considered by many to be deviant behavior, napping has traditionally gotten a bad rap, disparaged as the unfortunate artifact of an overindulgent meal, stifling midday heat, or sheer laziness. One is "caught" napping—okay for kids, but for adults, a sign of weakness, sloth, or senility. Even the medical profession has traditionally viewed the tendency to nap with suspicion, indicative of poor sleep hygiene or disorders such as sleep apnea or narcolepsy.

I'm happy to report that in the past few years napping has achieved new status. Research shows that naps not only ensure a break at a time of day when we're definitely not at our best, they also have powerful recuperative effects on performance, out of all proportion to their duration.

Some wise souls have long suspected as much.

Napping is common in traditional cultures, from Papua New Guinea, where people favor a two-hour nap at noon, thus avoiding the scorching midday equatorial sun, to chilly Patagonia, where the Yahgan, when tired, will lie down for a nap anywhere and at any time, to the inhabitants of Pukapuka, an atoll in the Cook Islands, who differentiate more than thirty-five kinds of dozing based on soundness of sleep and the position and movement of the sleeper.

"You must sleep sometime between lunch and dinner," advised Winston Churchill, "and no half-way measures. Take off your clothes and get into bed." In World War II, the British prime minister managed to be alert and awake at all hours of the night. "I
had
to sleep during the day," Churchill said. "That was the only way I could cope with my responsibilities ... Don't think you will be doing less work because you sleep during the day ... You get two days in one—well, at least one and a half, I'm sure." President Lyndon Johnson, too, is said to have slipped on his pajamas at midday in order to sleep soundly for half an hour, which gave him the strength to work into the night.

Claudio Stampi, an Italian sleep researcher, has explored tales—some probably apocryphal—of famous personages who existed solely on sleep stolen during naps. Thomas Edison, for instance, was an incurable nighttime insomniac who worked incessantly to accrue patents, including the one he's chiefly known for, which badly aggravated his own condition. Instead of sleeping eight hours a night, which he considered a "deplorable regression to the primitive state of the cave-man," Edison got by with frequent naps. Leonardo da Vinci is said to have slept for fifteen minutes or so every four hours, for a daily total of less than two hours' sleep. By so doing, he may have gained twenty years of bonus work time during his sixty-seven years of life.

It may not feel as if naps have a reviving effect; sleep inertia from a nap often leaves one feeling groggy. But we're generally not good judges of our own restedness. As the pioneering sleep researcher William Dement points out, study after study demonstrates that naps enhance alertness, mood, vigilance, and productivity in the later hours of the day, particularly for night-shift workers and for those forced to work for long periods.

According to Dement, important findings emerged when researchers at
NASA
tested the effects of napping on pilots flying long distances across the Pacific at night. During such long-haul flights, the reaction times of cockpit crews typically plummet, and pilots frequently fall into "microsleeps," brief episodes of sleep 3 to 10 seconds long. In the
NASA
study, some crews were directed to rest for 40 minutes during transoceanic flights, netting an average of about 26 minutes of sleep. A control group of cockpit staff on similar flights got no rest. On the no-rest flights, crews experienced a combined total of 120 microsleeps during the last one and a half hours of the flights, including 22 in the final half hour, when the plane was descending to land. The napping flight crews experienced only 34 microsleeps in the same period, and none in the last half hour. Their reaction time, vigilance, and alertness also improved.