Sleep is as important to our lives as the food we eat and the air we breathe. We need it for growth and repair of the body, healthy brain function, and the consolidation of memories.
What happens during sleep?
Many important body processes occur while you are asleep. During normal sleep, you cycle through what's known as rapid eye movement (REM) sleep and non-REM sleep.
It's during REM sleep that most dreaming takes place. The eyes dart back and forth, though the rest of the body is very still. The brain is active and working to seal in memories.
But before deeply restorative REM sleep can occur, your body must pass through the following stages of non-REM sleep, each of which serves its own vital role:
Stage 1 represents a bridge from wakefulness to sleep. It’s a very light sleep—what Michael Breus, Ph.D., author of Good Night: The Sleep Doctor’s 4-Week Program to Better Sleep and Better Health, calls “your entrance into sleep.” It lasts from five to 10 minutes or so.
Stage 2 marks the onset of sleep. Your breathing is regular but your heart rate slows down a bit, and your body temperature drops. It is during this stage of light sleep that you begin to disengage from your surroundings.
Stage 3 and Stage 4 are characterized by a deeper level of slumber, referred to as delta sleep. Blood pressure drops, breathing slows, and the muscles relax. It's in these stages that the body produces growth hormone, which is responsible for proper development, and has a chance to repair and build bone, muscle, and other tissues. The immune system also has an opportunity to recoup.
So how do all of these different stages play out? “During sleep, the brain goes through a dance,” says Dr. Breus. “It shifts from being awake to Stage 1 to Stage 2, Stages 3 and 4, and back to Stage 2, and then to REM."
REM sleep typically takes place about 90 minutes after falling asleep, and can last from 10 minutes to 60 minutes—with each successive REM period getting longer. On average, adults go through a total of five cycles of non-REM and REM sleep in any given night of normal sleep.
The amount of sleep needed for basic health varies naturally a bit from person to person, but also depends in part on such factors as age. For example, toddlers need about 11 to 14 hours of sleep a day, while teenagers need eight to 10. Adults usually need seven to nine hours of sleep, and people over age 65 typically manage well with seven to eight.
When sleep gets derailed
By definition, insomnia includes problems falling or staying asleep, waking too early and being unable to go back to sleep, or having sleep that doesn't feel restorative. While insomnia is not the only type of sleep disorder, it is the most common one. (Some others, for example, are obstructive sleep apnea, which involves blockage of airflow during sleep; restless legs syndrome, characterized by an urge to move your legs at night; and narcolepsy, a disorder that causes overwhelming drowsiness during the day.)
Insomnia can be acute or chronic (see "Terms to Know" at right). Either way, if you're not experiencing the normal cycling of the sleep stages, you will likely feel some immediate effects. These may include fatigue, daytime sleepiness, moodiness, upset stomach, headache, and problems concentrating and paying attention.
The American Academy of Sleep Medicine reports that people with insomnia often are not getting a full night’s sleep, even though they’re in bed for a long time. “Many people we see are spending nine hours in bed but only sleeping for five,” says Robert S. Rosenberg, D.O., medical director of the Sleep Disorders Center of Prescott Valley in Arizona.
At a certain point, insomnia can lead to serious health problems. For example, lack of sleep can disrupt the body’s endocrine system responsible for regulating appetite and blood sugar, among other functions. “When you have insomnia and sleep deprivation, levels of the hormone ghrelin, which makes you feel hungry, increase, and levels of leptin, which makes you feel full, decrease,” explains Raj Dasgupta, M.D., assistant professor of pulmonary, critical care, and sleep medicine at the University of Southern California in Los Angeles. In fact, research from Texas Tech University in Lubbock has found that sleeping less than seven hours per night doubles a person’s risk of becoming obese.
Over time, sleep loss can also weaken your immune system. “Studies have shown that people who suffer from sleeplessness mount a weaker immune response when getting vaccinated,” says Dr. Dasgupta. “Therefore, they may be less protected from illnesses.”
Another potential casualty of sleep difficulties can be the heart. For example, women who sleep five or fewer hours a night have a 30 percent greater chance of developing coronary heart disease. That's according to the long-running Nurses’ Health Study, one of the nation's largest investigations into chronic disease risk factors in women.
You're not alone
Approximately 1 in 3 adults have insomnia, according to the American Academy of Sleep Medicine. And the population most likely to be affected are middle-aged and older adults, although people of basically any age are susceptible.
In general, more women than men have insomnia, particularly in midlife. Beginning with perimenopause, the approximately four-year stretch that precedes menopause, “there are abrupt changes to hormones, and these can be accompanied by night sweats, insomnia, and unrefreshing sleep that lasts for weeks to many months,” says Michael J. Decker, Ph.D., R.N., a sleep researcher and associate professor at Case Western Reserve University in Cleveland, Ohio.
Insomnia that's secondary
Many people don't simply have insomnia, but are dealing with another illness that is actually at the root of their sleep issues. This is secondary insomnia. Underlying conditions such as diabetes, asthma, and chronic pain are in this category. In this situation, the insomnia is ideally addressed by treating the illness itself along with the sleep problems.
Other common causes of secondary insomnia include depression and anxiety. “For many years, health professionals saw insomnia as a symptom rather than a cause of depression,” says Dr. Decker, adding that more recent research indicates that the influence goes both ways. To complicate matters, antidepressant medications can be a source of sleeplessness, too,” notes Dr. Dasgupta.
In fact, it is not uncommon for sleep problems to surface as a side effect of medications; other common culprits include drugs taken for colds and allergies, heart disease, high blood pressure, and thyroid disease.