Get a good night's sleep for happier days

Know somebody who likes to brag that he can get by on six hours of sleep a night?

Tell him that men who sleep less than seven hours a night have a 26 percent greater death rate over a two-decade period than men who sleep seven to eight hours a night.

And children who don't get enough sleep are more likely to be overweight and to have behavioral problems.

And people who do rotating-shift work have lower levels of the hormone serotonin, a condition associated with anxiety and depression.

These findings, all published in the journal Sleep in the past seven months, are part of a rapidly expanding body of knowledge about the physiology of sleep and the importance of adequate sleep to good health.

"Shift work was just added to the list of risk factors for cancer by the CDC [Centers for Disease Control and Prevention]," says Dr. Jerrold Kram, a director of the National Sleep Foundation. "It just suggests the increasing recognition of how profoundly sleep affects our lives."

And it's not just arcane statistics about risk factors and sleep that are accumulating. There are 83 recognized sleep disorders, including sleep apneas, insomnias, circadian-rhythm disturbances, narcolepsy, restless leg syndrome and plain old wake-the-neighborhood snoring. Physicians such as Kram are putting this knowledge to use, making sleep medicine one of the fastest-growing medical specialties over the past decade.

You need all five sleep stages

"We used to think that sleep was a dormant period of time, and we're finding out that there are a whole lot of things that go on during sleep," says Dr. David Ostransky, a pulmonology and sleep-medicine specialist in Fort Worth, Texas.

Saying "a whole lot" goes on during sleep is like saying that war is "unpleasant."

There are five stages of sleep, according to the National Sleep Foundation (NSF), four non-REM stages and REM (rapid eye movement) sleep, and sleepers cycle through the stages about every 90 to 100 minutes.

Stage 1: A transitional stage between waking and sleep. Your brain waves and muscle activity slow. Sometimes people's bodies jerk just before they fall asleep.

Stages 3 and 4: These delta sleep stages are when body restoration and repair occurs. Temperature drops even further during this phase, brain waves are slow and there is decreased muscle tone. Fibromyalgia may be associated with poor delta sleep, Ostransky says. People awakened during this deep sleep are often groggy and disoriented. Night terrors occur during this sleep stage.

Stage 5: REM sleep is a period of fast brain waves; rapid, shallow breathing; and the rapid eye movements it's named for. Dreaming, believed to be a way of organizing the day's experiences, says Ostransky, occurs during REM sleep. Muscles become temporarily paralyzed during REM.

These stages of sleep are repeated four to six times during the night, but not in exactly the same proportion. The first REM sleep is short, just seven minutes or so, but REM sleep takes up a larger and larger portion of the cycles as the night goes on, Ostransky says, which is why you're often dreaming when your alarm clock goes off.

And it's not just the amount of sleep, but the distribution of sleep stages, that's important for health. People who get inadequate delta sleep, or REM sleep, wake up feeling unrestored, Ostransky says.

Don't mess with your circadian rhythm

Cycles of light and dark are what keep the suprachiasmatic nucleus properly set so that you will go to sleep at 11 and wake up at 7. The human body, deprived of sunlight and clocks, wouldn't naturally keep a 24-hour schedule.

Teenagers are particularly prone to circadian-rhythm problems, and their night-owl tendencies are at least partly biological, says sleep foundation spokesman Kram.

Light is the chief, but not the only, clue for the body's inner clock, according to the American Association of Sleep Medicine website. Zeitgebers are the name for other circadian-rhythm influences, and they include meals, exercise and routine activities.

People with chronic insomnia may be helped by sticking to regular times for meals, exercise and bedtime routines.

Hormones out of whack

Many of these regulatory hormones are secreted at night or during periods of sleep, and sleep disorders or life situations such as shift work can affect the proper sequence of hormone release, the sleep foundation says.

Melatonin, a hormone secreted by the pineal gland in the brain in reaction to darkness, helps promote sleep, but has other functions, as well. Disruptions in melatonin production may be the reason why shift work is associated with an increased risk of cancer.

Growth hormone is released during the delta sleep stages, Ostransky says. Children need it, but adults also require it to repair the body and regulate muscle mass.

The stress hormone cortisol falls as the body enters sleep and then rises in the morning before waking, Kram says.

Hormones involved in the reproductive cycle, including luteinizing hormone and follicle-stimulating hormone, are released during sleep, according to the foundation.