Some 130 million American adults accumulate sleep debt like gamblers racking up IOUs. According to the statistics, each weekday night Americans average an hour and six minutes less than the eight hours that sleep experts recommend, and each weekend night almost half an hour less. By the end of the year, that adds up to over 330 lost hours of rest.

Most people know that lack of sleep makes them punchy. But they are dangerously unaware of the risks to their health. Latest research shows that sleep may be the third essential component of a long and healthy life, up there with a good diet and regular exercise.

The sleep-deprived multitudes are cutting short a natural rhythm that begins in the evening, when the pineal gland in the brain releases melatonin, a hormone signaling that it's bedtime. As the head hits the pillow, breathing slows and the brain relaxes. An EEG of its electrical activity shows a change from the rapid beta waves of daytime to slower alpha waves. Then alpha waves disappear, replaced by the even slower theta waves of stage-one sleep. From there, it's an elevator ride through sleep's various states. Next comes stage two, which larger EEG squiggles, where the sleeper lolls for ten to fifteen minutes. Stage three, a deep sleep with lazy delta waves, lasts five to fifteen minutes. Then it's down to the cellar, a relaxed descent into stage four for half an hour or so, then back up through stages three and two. After this 90-minute ride, we dream before beginning a second descent. And we ride up and down all night.

Thomas Wehr, a researcher on biological rhythm, did a four-week sleep experiment in which volunteers spent 14 hours in bed. During the first few days, they slept about 11 hours each night. They slept less through the second and third weeks, as they finished paying back an average of 17 hours of sleep debt accumulated before the experiment began. By the fourth week, they were asleep an average of eight hours and 15 minutes a night.

Researchers are beginning to understand what we lose by giving up sleep. Earlier studies showed that people who stayed awake for days could recover quickly, leading experts to believe there were few long-term health consequences. But recent research has begun to home in on today's reality: what happens to people who shortchange their sleep needs a little, almost every day? In 1999 Eve Van Cauter, a sleep researcher at the University of Chicago, published a groundbreaking study in The Lancet in which, for six nights, young men spent only four hours in bed. During that week, their blood samples showed impaired glucose tolerance: they were in a prediabetic state. Van Cauter believes that sleep loss is partly involved in the rising rate of obesity. One link is growth hormone, which controls the body's proportions of fat and muscle. Lack of sleep could drive down growth hormone, accelerating the paunch process. Another hormone, leptin, tells the body when it should feel full. With the low levels of sleep debt, your body will crave carbohydrates even though you've had enough calories.

Studies also associate lack of sleep with changes in immune response. Robbed of all sleep, laboratory rat will die in about three weeks, apparently from infection. Human studies show that inadequate sleep changes white blood cell counts and immune-response modifiers. This may be evidence that the body is having trouble fighting infection.

Not enough sleep might even boost cancer risk. There may be a connection between the increase in breast cancer and hormone cycles disrupted by late-night light. This may explain why blind women are less prone to breast cancer than sighted women.

Those who try to cheat sleep may be getting less out of their extra waking hours than they think. One may get foggy on any less than eight hours of shut-eye. That hour saved by sleeping less is more than lost by decreased functionality.

It's easy to tell if you're sleep-deprived. If you can lid down in the middle of the day and fall asleep in ten minutes, you have shortchanged yourself on sleep. Catching up is basic arithmetic. For every hour — or fraction — under eight, you need an equal extra amount of sleep soon after. If you have trouble sleeping, stay away from caffeine and alcohol late in the day. Your doctor may prescribe sleeping pills, usually on a short-term basis. Scientists are divided on the use of melatonin, though most agree that the 3-mg dose is higher than necessary. Researchers in MIT reported that a low dose of melatonin — a tenth of the standard pill — helped elderly people with insomnia get a good night's sleep. A dose of 0.3 mg completely restored sleep to normal, 0.1 was less effective, and 3.0 was also less effective.

Sometimes a nap can boost your alertness. The hours between 1 p.m. and 3 p.m., worldwide siesta time, are good for sacking out. A short nap — up to 30 minutes — works best. After that, you'll be in deep sleep and may feel groggy upon awakening.

But naps don't address the underlying problem. Every week, Americans rack up more than a billion hours of sleep debt. Eventually sleep researchers may come up with an easy solution. They hope to develop drugs that could help six-hour-a-nighters enjoy the alertness and physical well-being that comes from a full night's rest.The "perfect" bedroomFor sleep to rejuvenate, it should be continuous — an uninterrupted six hours is often more restorative than eight hours of fragmented sleep. Here's how to prepare your bedroom for that elusive deep sleep.

Noise If not eliminated entirely, bedroom sounds should be low and consistent. Try earplugs, or tune a radio between two FM stations for white noise.

Light Use dark fabric to block windows. Eye shades may also help.

Temperature A hot bedroom may interrupt sleep and even induce nightmares. The ideal temperature is about 65 to 70 degrees.

Décor Hide illuminated alarms to avoid clock-watching during the night. And keep the bedroom clutter-free. Piles of paper may create stress.

Pillows Sleeping on your stomach can cause back pain, so try lying on your side or back. If you're a side sleeper, your pillow should support your head and neck, keeping them aligned. For a back sleeper, it should be mostly under your neck, with your head almost touching the mattress. Fill down or feather into pillows — they offer the most adjustability.

Mattresses If you sleep with a partner, don't go for anything smaller than queen size. We turn some 40 to 70 times a night, and need room to move freely.

(Selected from U.S. News & World Report, October 16, 2000, written by Susan Brink)