Everyone knows good nutrition and exercise are essential to good health, but there's a crucial third component that's often overlooked: sleep. "People will say, 'I'll sleep plenty when I'm dead,' but when you're young is when you've got to sleep," says Cornell University psychology professor James B. Maas, Ph.D., author of Power Sleep (Villard, 1999). "Otherwise, you'll put wear and tear on your body, which is awfully hard to make up for later in your life."

Let's test your knowledge on how insufficient slumber can affect you -- and how to get a good night's sleep:

1. How many hours does the average woman sleep?

A. 6 hours, 10 minutes

B. 7 hours, 20 minutes

C. 7 hours, 2 minutes

D. 8 hours, 3 minutes

Answer: A. The 6 hours and 10 minutes that a typical woman sleeps each night is three hours less than she needs through age 25 (to accommodate effects of puberty and post-puberty hormones) and nearly two hours less than she needs after age 25. "For peak performance, eight hours of sleep is not the ideal," says Maas. "It's 9 hours and 25 minutes."

Women sleep four minutes less than men on weekdays and 14 minutes less on weekends. In the first year of motherhood, women lose 400-750 hours of sleep, and they sleep 50 minutes less each night than new fathers do. The lost sleep matters: The longest REM (rapid-eye-movement) period -- vital for memory, learning and mental performance -- takes place in the last two hours of a 7- to 8-hour sleeping bout.

2. To enhance sleep, what's the best time for aerobic exercise?

A. 7-9 a.m.

B. 4-6 p.m.

C. 7-9 p.m.

D. Any of the above

Answer: B. Aerobic exercise raises your body temperature and metabolism; sleep occurs with the opposite. So when you work out in the late afternoon or early evening, you experience a steep drop in temperature by the time you go to sleep, making your snooze time deeper and more satisfying.

With a good night's sleep, you'll also have more energy to work out harder, says Joyce Walsleben, Ph.D., director of the New York University Sleep Disorders Center. In a Stanford University study, men and women who did 30-40 minutes of moderate aerobic exercise for 16 weeks fell asleep 12 minutes faster and slept 42 minutes longer than sedentary subjects.

3. If you don't get enough ZZZs, you'll:

A. Lose weight

B. Retain water

C. Age more rapidly

D. Experience skin problems

Answer: C. A University of Chicago study found that when healthy men ages 17-28 were restricted to four hours of sleep for six nights in a row, their blood pressure, blood sugar and memory loss increased to levels usually associated with 60-year-olds. Fortunately, after a few nights of 12-hour slumbers, they were able to turn the clock back.

Still, skimping on sleep regularly increases your risk of colds and flu while reducing your creativity and reaction time. If sleep deprivation lasts more than six months, you'll become four times more vulnerable to depression, anxiety, even substance abuse. Alas, the one thing you don't lose if you fail to snooze: weight. You're more likely to nosh on sweets to fight fatigue. And less sleep makes weight loss harder: Cortisol, a stress hormone, is elevated when you don't get enough sleep; this, in turn, increases the activity of a key enzyme (lipoprotein lipase) that regulates fat storage.

4. Which of the following will help you fall asleep when you're stressed?

A. A glass of wine

B. Deep belly breaths

C. Keeping a journal

D. Watching a dull documentary

Answer: B. Belly breathing -- slow, deep breathing from your diaphragm -- calms you and slows your heart rate. So does progressive relaxation, which is tightening and relaxing your muscles group by group, from head to toe. Or, set aside time each day, perhaps 10 minutes at lunch, to list your frets and possible solutions in a "worry book." "It's easier to shut anxieties from your mind if you've worked on them and have a time to devote to them tomorrow,'' says Derek Loewy, Ph.D., a sleep researcher at the Stanford University Sleep Disorders Clinic. Other relaxants include a hot bath, pleasurable sex or mental imagery. Skip the nightcap in the three hours before retiring. Though alcohol can make you fall asleep faster, your ZZZs will be shallow and fragmented.

5. How often does a healthy young woman wake up each night?

A. Never

B. 1 time

C. 2-3 times

D. 4-5 times

Answer: D. Men and women of all ages wake up four to five times nightly, although they may not even realize it. When you wake up, don't look at the clock. Instead, try a variation on the sheep-counting theme: Mentally tabulate the number of black slacks you own or something else that's easy yet mentally engaging. If you wake up for long periods, try going to bed later consistently and waking up at the same time each morning. Once you've slept through 90 percent of the night, you can add 15 minutes to the beginning or end of your sleep time. Just make sure you're getting the nine-plus hours you need for good health.

6. Which is the biggest sleep deterrent in your bedroom?

A. A pet

B. A man


D. An electric fan

Answer: C. TV stimulates your alertness. Plus, the flickering light keeps you awake and programs your circadian clock to keep you up later. Worse, if you fall asleep with the TV on, the light will make your sleep shallow and unsatisfactory.

But men also can be a problem if they snore, a bother to 22 percent of women (and only 7 percent of men) with bed partners, according to a National Sleep Foundation survey. Snoring mates cost their partners one hour of sleep nightly. Solutions include earplugs for you, nasal strips for him (to keep nose passages open) and a mattress made of individually wrapped coils for the both of you. The mattress reduces the rock 'n' roll of two people tossing and turning.

Pets may disturb sleep, but only if they're hyperactive, your bed is too small or they aggravate your allergies. The fan will rouse you only if it's chugging. More likely, the humming will lull you to sleep.

7. Put these beverages in order, from the one with the most caffeine (a major sleep disruptor) to the one with the least.

A. Mountain Dew, 12 ounces

B. Iced tea, 12 ounces

C. Starbucks Café Latte, 8 ounces

D. 7Up, 12 ounces

Answer: C, B, A, D. Latte (89 mg), iced tea (70 mg), Mountain Dew (55 mg), 7Up (0 mg). Caffeine alters your circadian rhythm and combats adenosine, a chemical that builds up in the body over the course of the day and encourages sleep. Other culprits include Sunkist orange soda (41 mg in 12 ounces), Ben & Jerry's no-fat coffee-fudge frozen yogurt (85 mg per cup), Excedrin Migraine (65 mg) and Maximum Strength Midol Menstrual (60 mg).

So, how did you score?

Give yourself 10 points for every correct answer. If you scored:

60-70 points Excellent. You're most likely getting your needed ZZZs.

50 points Good. Let's hope you put your knowledge into practice.

30-40 points Average. Like most of us, you're shaving snooze time and it shows.

0-20 points Poor. Our Rx: Sleep on it and try our test again.