Insomnia is almost always the result of an underlying condition and discovering the cause is the most important step in relieving insomnia. Dozens of causes for insomnia can be grouped roughly into four categories: psychologic problems, acute events or factors that precipitate temporary insomnia, medical or biologic disorders, and conditions that perpetuate insomnia. Restless legs syndrome is related to the central nervous system, but the specific mechanisms that cause this problem are still unknown. Genetic factors may be involved.

Psychologic Causes of Insomnia

A large percentage of chronic insomnia cases prove to have a serious psychologic or psychological basis. The disorders that most often cause insomnia are chronic anxiety, depression, and bipolar (manic) depression. At least 70% of people with depression complain of insomnia. One study found that 14% of people with insomnia (as well as 10% of people who sleep excessively) were depressed. Anxiety disorders affect as many as 25% of people with insomnia. 

Precipitating Factors of Transient Insomnia 

Adjustment Sleep Disorder. Affecting as many as 35% of American adults at some time, adjustment sleep disorder is one of the most common causes of short-term and transient insomnia. This form of sleeplessness is a reaction to change or stress. The precipitating factor could be a traumatic event such as acute illness, injury or surgery, or the loss of a loved one, or it could be a minor event, including extremes in weather, an exam, traveling, or trouble at work. In such cases, normal sleep almost always returns when the individual recovers from the event or becomes acclimated to the new situation. 

Jet Lag. Air travel across time zones often causes insomnia. After long plane trips, one day of adjustment is usually needed for each time zone crossed. Traveling west, to earlier times, seems to be less traumatic than going east to a later time, because it is easier to lengthen a circadian phase than to shorten it. 

Working Conditions. In one study, people on night shifts or on schedules of two- and three-shifts tended to suffer more from sleep-related problems, including insomnia, than those on day shifts. Another study found that 53% of night-shift workers fall asleep on the job at least once a week, implying that their internal clocks do not adjust to unusual work times. A recent Japanese study reporting on different aspects of insomnia found that excessive computer work was associated with all forms of insomnia. People who were overinvolved with their work tended to have trouble falling asleep and they tended to awaken earlier than average.

Medications. Insomnia is a side effect of many common medications, including over-the-counter preparations that contain caffeine. People who suspect their medications are causing them to lose sleep should check with a physician or pharmacist. 

Medical and Physical Conditions That Cause Insomnia 

Medical Conditions. Many common medical problems (and some of the drugs that treat them) can cause insomnia, including allergies, arthritis, heart disease, hypertension, asthma, rheumatologic conditions, Alzheimer's disease, Parkinson's disease, hyperthyroidism, and attention deficit hyperactivity disorder. 

Genetic Factors. Sleep problems among identical twins are more likely to be connected than among fraternal twins, indicating that sleep disturbances probably have a genetic component. 

Hormonal Fluctuations in Women. Fluctuations in female hormones play a major role in insomnia in women. Progesterone promotes sleep, and levels of this hormone plunge during menstruation, causing insomnia, and rise during ovulation, when women may be sleepy. During pregnancy, progesterone levels in the first and last trimester can disrupt normal sleep patterns. Insomnia can be a major problem in the first phases of menopause, when hormones are fluctuating intensely. Hot flashes, sweating, and a sense of anxiety can awaken women suddenly and frequently at night during the first months of menopause. Insomnia may also be perpetuated by psychologic distress provoked by this life passage. 

Delayed Sleep-Phase Syndrome. Delayed sleep-phase syndrome is the term for a circadian clock that runs late but reliably. People who have this condition fall asleep very late at night or in early morning hours, but then they sleep normally. 

Perpetuating Factors 

Psychophysiological Insomnia. Psychophysiological insomnia, which affects about 5% of people, is the revolving door of sleeplessness, caused by insomnia. An episode of transient insomnia disrupts the person's circadian rhythm, and the sufferer comes to associate the bed not with rest and relaxation but with exhaustion and a terrible struggle to get to sleep. After such a cycle is established, insomnia becomes a self-fulfilling prophecy that can persist indefinitely. The desire to fall asleep leads to anxiety, which, in turn, perpetuates sleeplessness. Some studies indicate that people susceptible to psychophysiological insomnia have characteristics, including a faster than average heart rate, a tendency to awaken easily, and a higher body temperature, that make them more prone to this cycle. 

Caffeine, Alcohol, and other Substances. Certain lifestyle habits can lead to sleeplessness. Caffeine most commonly disrupts sleep. An estimated 10% to 15% of chronic insomnia cases result from substance abuse, especially alcohol, cocaine, and sedatives. One or two alcoholic drinks in people who are not in danger of alcoholism may help reduce stress and initiate sleep. Excess alcohol, however, tends to fragment sleep and cause wakefulness a few hours later. Alcoholics often suffer insomnia during withdrawal and, in some cases, for several years during recovery. Nicotine can cause wakefulness and quitting smoking can also cause transient insomnia. It has been suggested that if sleeping could be improved during withdrawal from smoking, then perhaps it would be easier to quit smoking. 

Decreased Melatonin. Levels of melatonin, the hormone that helps control sleep, decrease as one ages. It is highest in children and slowly declines over time, until by age 60 very little is produced. 

Artificial Light. It is well known that a person's biologic circadian clock is triggered by sunlight and very bright artificial light to maintain wakefulness. A recent study indicated that even dim artificial light may disrupt sleep. 

Childhood Insomnia. One recent study suggested that parents who do not regulate bedtime schedules may encourage a tendency for sleeplessness in their child. In such cases, however, the insomnia is usually mild and occasional. Severe sleep disturbances were associated with the temperament of the child. Children with such sleep problems were more high-strung, intense, and easily upset than other children. The study did not examine, however, whether these traits might have derived from problems in the home, such as marital discord or parental depression.