For an astonishing number of Americans, fitful nights of tossing and turning are the norm. According to a National Sleep Foundation poll, more than half of the population suffer from some kind of sleep disorder. And it's particularly bad for women: 3 out of 10—50 percent more than men—complain that drowsiness impacts their daily routines. "Women are probably the most sleep-deprived creatures on earth," says Dr. Joyce Walsleben, director of the New York University School of Medicine's Sleep Disorders Center and coauthor of A Woman's Guide to Sleep: Guaranteed Solutions for a Good Night's Rest. "We tend to have more restorative sleep than men," notes Walsleben, 61, "but we have other things that enter our lives to disrupt it." Still, she says, there are effective ways to combat the demons that keep us up—both biological and emotional. She spoke recently with PEOPLE's Jennifer Frey.

What is sleep deprivation?

It's defined as the lack of adequate sleep. People need between 7 and 10 hours, and the average woman age 30 to 60 gets just 6 hours and 41 minutes a night during the workweek. If you haven't slept well, you're sluggish, slower, irritable. Studies suggest that 17 hours of wakefulness, which is our average day, would be equivalent to a blood alcohol level of .05 in terms of performance. In 24 hours of wakefulness you'd become legally drunk. Also, sleep is a healing process that affects the immune system. You may be more prone to illness if you don't sleep enough over a period of time. Some data show that sleep deprivation may also speed aging and affect memory.

How can you tell if you are sleep-deprived?

If you're falling asleep at your desk in the afternoon, if you can't stay awake after dinner, if you're falling asleep in the car or on the train—those are the signs.

Why do more women than men suffer from it?

First of all, women have a greater tendency to have depression, muscular pain and chronic fatigue, all of which can disrupt sleep. Sleep loss also coincides with life changes: For new mothers—who are usually the ones who wake up with their babies—up to 700 hours of sleep may be lost during the first year. During menopause women tend to develop fragmented sleep and insomnia. Another cause is stress. Men handle it differently, more outwardly. They may steam and rant. Women are more likely to keep it in. Most crucially, our hormones may fluctuate monthly or daily—if not hourly. Some of us are very sensitive to any slight adjustment, and this fluctuation can be very disruptive to sleep. On the other hand, women have more deep, restorative sleep and dream longer than men, which may be factors in why we live longer.

What's the best way to deal with these hormonal shifts?

It's common for women to deny their menstrual cycle. It comes on the same day every month, and yet they're always surprised. Women should understand that this thing is going to be around for a while and take measures to preempt the problems. If you suffer from bloating, watch what you eat, take less salt and drink more water. If you anticipate cramps, take medication before going to sleep. Estrogen replacement is certainly helpful with fragmented sleep during menopause, but its safety factor is still in question. Every woman is faced with the decision whether to take the hormones.

How do you cure insomnia?

Set a regular wake time, meal time and work schedule. Don't go to bed unless you feel that you can fall asleep; once you are sleeping consistently through the night, you can gradually move your bedtime up. Cover the clock, which only reminds you of every second you're still awake. Also, watch your diet. Avoid nicotine and alcohol. If you have insomnia for just one night, the trick is to forget it, go about your business, go to bed at a regular time the next day—and sleep will come.

What about over-the-counter drugs?

I don't recommend them, though many physicians do—particularly antihistamines. It's overkill. Most people don't know what the interactions are with other health issues like breathing disorders and hypertension, or with other medicines. The same is true with herbs. Just because an herb is "organic" and you find it at health food stores doesn't mean it's good.

Can you make up for sleep lost during the week by snoozing until noon on Saturday?

You probably can't get it all back. It takes several days of sleeping longer to blow off the sleep debt. You will be better, but one night is not going to make that much of a difference.

Do we need less sleep as we get older?

I think we need as much. We just get less.