Sleep, that knitteth up the ravelled sleeve of care.

William Shakespeare wrote these words, no doubt after one smashingly restful night. And we admit, he had a point.But in these days of dual-income families - when we barely have time to microwave dinner, let alone fluff up our pillows and nurse a glass of warm milk - who has time to indulge?

According to researchers, most of us sleep 60 to 90 minutes less than we should each night. By the end of the week, it's as if we've missed a full night's sleep.

"It's very prevalent," says Eric Hoddes, a sleep expert with AMI Presbyterian Aurora Hospital Sleep Disorders Lab in Denver. "Look around at your friends. Out of 10, nine will probably have that problem on any given week.

"They stay up late working on a project, get caught up in a book and keep reading."

Our careers don't help matters. According to one Michigan State University study, a 25 percent wage increase reduces the amount of time we sleep by about 10 minutes. Career women sleep about 5 percent less than their male counterparts.

What the consequences of cutting back? We spoke with sleep experts. Their answers follow.

Why should I be concerned about my sleep habits?

Although researchers are only beginning to understand the mechanisms of sleep and how it restores our bodies, they never downplay its significance.

"One of the primary bodily functions is waking and sleeping," says Lawrence Scrima, director of the Rose Hospital Sleep Disorders Center in Denver.

What happens without enough sleep?

People who haven't had enough sleep tend to make more errors at work, are less able to concentrate, think clearly, solve problems. They can be irritable, depressed, slow to respond.

"You're not as witty as you normally are," says Tom Cordas, director of Denver Presbyterian Hospital's Sleep Disorders Center.

They can also be more susceptible to colds, flu and other diseases. Dr. Martin Reite, director of the University of Colorado Health Sciences Center Sleep Disorders Center, notes that a study by the University of California at San Diego found that activity of natural killer cells, one of the first defenses against cancer, decreased with sleep deprivation. However, he cautions, a direct link between this lack of activity and cancer has yet to be established.

But there's no question lack of sleep can lead to tragedy. At a recent Sleep Loss and Driving Safety seminar, experts said sleep played a key role in up to 400,000 traffic accidents a year.

"One of the peak times for air crashes is the early hours of the morning," adds Scrima, "when the tug for sleep pulls heavily on pilots."

And if that doesn't impress you, consider this: The Three Mile Island disaster occurred at 4 a.m., Chernobyl at 2 a.m. and the Exxon Valdez around midnight.

How much sleep do I need?

Everyone is different. Some people can get by on four hours a night. Others need 10. The average is 7-1/2.

How much can I cut back on sleep, without feeling the effects?

Not much. Even a half hour can make a difference, says Hoddes. In one study, he says, participants who cut back a half hour of sleep per week complained of not feeling right. "They felt out of sorts, uncomfortable. When they were able to sleep as long as they wanted, they felt back to normal."

Those who can shake off the effects of 30 minutes' less sleep, adds Hoddes, will probably begin to feel them after an hour of deprivation, he adds.

"Just look at Daylight Savings Time, what happens when you have to spring forward and lose an hour of sleep. You hear people complaining for a week," he says.

Can I catch up on my sleep on the weekend?

Theoretically, it's possible, say experts. But practically speaking, don't count on it. For example, if you regularly need eight hours of sleep, but cut back an hour a night during the week, that means you'll need 13 hours on Saturday.

"Can you really sleep 13 hours?" says Scrima. "Do you ever do that?"

In addition, he adds, people tend to go to bed later on the weekend, making it unlikely they'll sleep long hours.

Even if none of this were true, experts warn that varying your sleep schedule disrupts body rhythms, causing further sleep problems.

Why can't I seem to sleep as well as when I was a child?

You're not imagining things. Children do sleep better, as a rule. Consider a toddler, who generally sleeps 12 hours a night. By adulthood, most of us sleep only 8 hours.

"The total amount of sleep time diminishes as we age," says Scrima.

And so does the quality of our sleep. Sleep consists of stages 1, 2, 3, 4 and REM, or dream sleep. In stages 3 and 4, we experience our deepest sleep. One study at Brown University found that between the ages of 10 and 20, we lose 40 percent to 50 percent of the deep sleep we had at 10. By our 60s and 70s, "it's not unusual to see no stage 3 and 4 sleep," says Cordas.

Adults are more easily aroused from sleep than children. And they suffer from more sleep disorders, such as sleep apnea, a condition that causes a person to awaken briefly, as many as 100 times a night.

- HOW TO GET A BETTER NIGHT'S SLEEP

Stress can make it difficult to get a good night's sleep. But you can improve your odds. Experts offer these tips:

- Determine how much sleep you require: Do this on vacation. Go to bed at a reasonable hour, then see when you naturally wake. Consider how you feel after different lengths of sleep: Are you rundown? Irritable? If so, you're not getting enough rest.

- Keep regular sleep hours: Many parts of our sleep are fixed to certain hours of the night. Dream sleep, for example, tends to occur the same time each night. Body temperature - which reaches its lowest point slightly before you wake up - also tends to drop on a predictable time table. We sleep best when our schedules are in sync with these cycles.

It's possible to change these timetables. "But it's not easy," says Eric Hoddes, sleep expert with AMI Presbyterian Aurora Hospital's Sleep Disorders Lab in Denver. "And it's not fast. It doesn't happen overnight."

Your temperature clock, for example, can take from 10 days to six weeks to change. To ensure you stay on schedule, get up the same time every morning. This way, you will most likely be ready for sleep the same time each night.

- Beware of naps: If you generally sleep well at night, an occasional nap won't present a problem. But those with sleep problems should avoid naps.

Satisfying part of your sleep debt by day will disrupt sleep at night.

- Avoid alcohol near bedtime: Alcohol may promote sleep initially, but it also suppresses dream sleep. As the night wears on, this has a rebound effect.

Your dreams can be more intense, nightmarish. The second half of your sleep will be disturbed.

- Avoid caffeine and nicotine: Both have stimulant effects that last hours after ingestion.

- Avoid sleeping pills.