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What Is Insomnia?

After infancy, humans function the way the world turns — on a natural cycle that repeats itself about every 24 hours. During this daily cycle — known as the circadian rhythm — most adults sleep between six and eight hours, usually at night and without interruption. A few nights of poor sleep do us no harm, but prolonged insomnia can have serious consequences. Insomnia is one of the most commonly reported health problems: About one in three people encounters sleep problems in a given year, and women are affected twice as often as men. Because sleep patterns change as we age, most sleep problems are reported by the elderly.

Insomnia can be described in terms of both duration and severity. Transient insomnia is associated with a temporary disturbance of one's normal sleeping pattern — caused, perhaps, by travel or relocation — and usually lasts no more than several nights. Short-term insomnia, lasting two or three weeks, can accompany worry or stress and typically disappears when the apparent cause is resolved. Chronic insomnia is a more complex problem with potentially serious effects, including immune disorders: When people are deprived of sleep over long periods, the body's production of natural killer cells — an important part of the immune system — becomes suppressed, potentially lowering resistance to disease.

What Causes It?

Insomnia may be caused by physical illness, a stress-filled lifestyle, excessive caffeine consumption, or chronic pain; or it may simply be the result of poor sleeping habits, such as napping during the day and going to bed at irregular hours. It is often linked to alcohol or drug abuse and to certain medications. Psychological factors alone account for about half of all insomnias evaluated by sleep therapists. For example, stress brought on by situations like a troubled marriage, a chronically ill child, or an unrewarding job can disrupt sleep. Depression is one of the most common causes of insomnia, and people with anxiety, schizophrenia, and other psychiatric disorders may also sleep poorly.

Certain physical illnesses interfere with sleep, especially disorders of the heart, lungs, kidneys, liver, pancreas, and digestive system. Other important physical causes include heartburn, chronic pain, and breathing disorders, such as sleep apnea. Insomnia often accompanies menopause, when sleep is disrupted by hot flashes or night sweats. Abnormal blood sugar levels can cause people suffering from diabetes or low blood sugar to wake up during the night.

Your own habits and lifestyle may be impeding your sleep pattern. Sedentary behavior and keeping an erratic schedule can contribute to insomnia, as can overconsumption of caffeine and other stimulants, or alcohol and other depressants. Over-the-counter drugs and prescription medications — from some blood pressure and heart drugs to thyroid hormones — can interfere with sleep, as can the accidental or deliberate misuse of sleeping pills, to say nothing of illegal drugs. There is even some evidence that using electric blankets can disrupt normal sleep.

Many illnesses are disturbing enough to the body that the normal sleep pattern is disrupted. Among them is the mysterious ailment called restless leg syndrome (RLS). Sufferers describe an unpleasant, creepy-crawly sensation when they lie still, causing an irresistible urge to move their limbs, even during sleep.

A common cluster of causes known as circadian rhythm disorders includes jet lag and shift-work sleep disorder. Airplane travel over several time zones disrupts the body's biological clock, which may not adjust itself to the time change for several days. An irregular work schedule or changing from day work to a night shift can also cause insomnia until a person adjusts to the new sleep pattern; some people never adjust completely. Environmental factors such as temperature, humidity, noise, light, and stale air can cause insomnia or reduce the quality of sleep, even when they don't actually keep you awake.

Transient insomnia, while not physically harmful, can become habitual and very difficult to resolve.