Researchers have discovered surprising facts about how adults sleep.

How much sleep?

You should sleep about 7½ hours per night. Anywhere from 7 to 8 hours is good. (Sleeping less than 7 hours is okay just if you compensate by taking a nap.)

If you sleep fewer than 6 hours, you’ll feel noticeably tired. Being tired hurts you in 5 ways:

Statisticians have this sad news: people who sleep fewer than 6 hours per night die sooner. So do people who oversleep (sleep more than 9 hours), because people oversleep just when they’re ill or depressed or previously deprived of sleep.

Unfortunately, most Americans undersleep on weekdays and try to compensate by oversleeping on weekends. The average American adult sleeps just 6.8 hours per weeknight, 9 hours per weekend night. Researchers consider that pattern to be unhealthy, like binge eating. Try to get a constant amount of sleep each night.

Philosophers blame American sleeplessness on electronics. We stay up later than our ancestors because of the invention of the light bulb and its 24-hour culture: car headlights, nighttime TV, the computer, and the Internet. America is always on, round the clock — and paying for it by getting underslept (and therefore ill, using poor judgment, accident-prone, obese, and diabetic).

When you feel tired

A brain chemical called adenosine makes your brain feel tired, so you want to sleep.

While you sleep, the adenosine binds to phosphorus to form adenosine triphosphate (ATP). After the adenosine gets used up (to make ATP), your brain no longer feels sleepy, so you wake up.

After waking up, you feel groggy for the first half hour, so don’t make any judgments then! After that first half hour, you’re fully functional.

While you’re awake, your body’s cells get energy by burning the ATP.

That burning makes the ATP break down into adenosine and phosphorus again. The gradual increase in adenosine and decrease in ATP makes your body gradually feel sleepy again, so you eventually feel very tired (“zonked out”) by the late afternoon (between 4PM and 5:30PM). Since you’re tired then, it’s a good time to take a nap (if your schedule permits). Your tiredness will tempt you overeat (by breaking your diet and eating a late-afternoon snack, especially as an excuse for having worked so hard throughout the day); but you should avoid that temptation: don’t eat then, just nap instead!

After 5:30PM, your eye senses the sky is darkening (even if you’re “blind”). Your eye passes the “darkness” sensation to your brain, into the hypothalamus’s back part, called the suprachiasmatic nucleus (SCN), which reacts by outputting a hormone to keep you awake through the early evening. That hormone makes you feel rejuvenated, less tired than during your zonk-out period. The SCN’s hormone level gradually increases. From 8PM to 10PM, you feel quite awake!

But at 10PM, your pineal gland increases its production of a hormone called melatonin, which quiets the SCN’s output, so you start feeling sleepy again and fall asleep at 11PM (since the melatonin takes an hour to make you sleepy). You sleep 7½ hours, so you arise at 6:30AM to start another day.

That’s the ideal sleep schedule for the typical American. Your own personal sleep schedule might differ, depending on how your hormones are working for you (and whether you recently got kissed, yelled at, or drunk).

Unique

Sleep’s purpose is to build your ATP levels, so you’ll have enough energy to function well throughout the day.

All animals sleep, even fish. (When a fish sleeps, it shuts down half its brain but uses the other half to keep swimming, so it can breathe.)

Humans are the only animals that typically sleep for 7½ hours in a row (and stay awake for 16½ hours in a row). Other animals sleep shorter and more often: they take lots of naps.

For example, cats rarely stay awake for more than 6 hours in a row; they take lots of catnaps. Cats can prowl at all hours of the day and night. Human eyes and noses are too poor to handle the night, so humans were built to just give up, sleep through the darkness, but think throughout the day.

Sleep positions

You can sleep in 4 positions:

Each position has its own advantages and problems. Here are the issues.…

Breathing The worst position for breathing is face up. When you’re face up, you’re most likely to snore, most like to suffer from sleep apnea (repeatedly interrupted breathing), and most likely to have your snot run down your throat (which worsens your cold or flu by infecting your throat & tummy).

The best position for breathing is face down, so the snot drips away from your body (onto your pillow or Kleenex) instead of down your throat.

Leg spasms When you’re sleeping, or trying to wake up, do you sometimes get painful spasms in your leg muscles? If so, the best way to avoid them (or stop them) is to go into the fetal position, where you look like a fetus: bend your legs, so your knees are near your tummy and your toes are turned toward your knees. One way to get into that position is to grab your toes and pull them toward your tummy. But you probably don’t want to spend all night grabbing your toes! The easiest way to approximate that position is to sleep on your side (curled up): so sleep facing your left or facing your right. Don’t sleep face up or face down.

Acid reflux If you eat too much, you might get acid reflux (where the acids in your stomach can’t fit inside your stomach, so they flow back up your esophagus and even into your mouth). The acids burn your esophagus, giving you a burning sensation (called heartburn because it’s near your heart, though it’s actually in just your esophagus). Those acids weaken your esophagus and make your esophagus more likely to get cancer. The problem is called gastroesophageal reflux disease (GERD). If the acids reach your mouth, they’ll eat away your teeth surfaces (the enamel).

To avoid acid reflux, many patients buy pills (or change diet or chew gum or get surgery or sleep on a slanted bed), but try this easy sleeping technique first: sleep facing your left. Here’s why:

Don’t sleep facing your right. (If you sleep on your right-hand side, your stomach is higher than your esophagus, and your stomach’s acids drip into your esophagus.)

Sudden infant death If you have an infant under the age of 1, make the infant sleep face up, to prevent sudden infant death syndrome (SIDS), even though the infant will sleep more soundly face down.

Comfort The only comfortable position is face up. Other positions scrunch part of your body: lying on your side crushes that side; lying face down strains your neck. Also, if you try to pamper yourself by lying on an electric message bed, the bed massages you well just if you lie face up.

Masturbation If you sleep face down, your genitals will rub against the mattress, leading to masturbation. That’s fun if you’re alone (but distracting if your bedroom is shared).

Summary So here’s the advantage of each position:

Most people change positions several times throughout the night. That’s natural and good, since staying in the same position too long can create bedsores. That’s why hospitals hire nurses to turn over the patients.

Insomnia

If you have trouble falling asleep, researchers recommend removing all distractions from your bedroom: avoid light, clocks, books, televisions, and food, so your bedroom is totally peaceful, boring, sleepy.

If you want to read a book or watch TV, do so in a separate room (or at least a separate chair), so your body gets in the habit of using your bed just for sleeping and sex. Instead of staring at an alarm clock and watching the minutes tick by, have a family member wake you — or at least turn the clock so you can’t see the time.

3 hours before you go to bed:

Though alcohol makes you fall asleep fast, the sleep it creates has poor quality, so you’ll tend to wake up at 3AM.

For a light bedtime snack, try milk, turkey, peanuts, or their variants (cheese, chicken, tuna, cashews, or soy), because they all contain an amino acid called tryptophan, which helps your brain produce serotonin (a chemical that helps you relax). Try them warm (by microwaving them or by putting peanut butter on toast), so your body gets warm & cozy then cools down again: the cooling will make you sleepy.

If a list of worries prevents you from sleeping, write the list down, so you feel organized and can analyze the list the next morning.

Most people who suffer from insomnia are old women (not young men).

These Websites have more suggestions to cure insomnia:

Details

For more details about sleep research, read Craig Lambert’s article “Deep into Sleep” (on pages 25-33 of Harvard Magazine’s July-August 2005 issue).