Seasonal Affective Disorder

Definition

Seasonal affective disorder (SAD) is a form of depression most often associated with lack of daylight in extreme northern and southern latitudes from the late fall to the early spring.

Description

Although researchers are not certain what causes seasonal affective disorder, they suspect that it has something to do with the hormone melatonin. Melatonin is thought to play an active role in regulating the "internal body clock," which dictates when humans feel like going to bed at night and getting up in the morning. Although seasonal affective disorder is most common when light is low, it may occur in the spring, which is often called reverse or spring-onset SAD. Recent research also indicates that SAD has a genetic factor; about 29% of cases in the United States run in families.

Causes & symptoms

The body produces more melatonin at night than during the day, and scientists believe it helps people feel sleepy at nighttime. There is also more melatonin in the body during winter, when the days are shorter. Some researchers believe that excessive melatonin release during winter in people with SAD may account for their feelings of drowsiness or depression. One variation on this idea is that people's internal clocks may become out of sync during winter with the light-dark cycle, leading to a long-term disruption in melatonin release. Another possible cause of SAD is that people may not adjust their habits to the season, or sleep more hours when it is darker, as would be natural.

Seasonal affective disorder, while not an official category of mental illness listed by the American Psychiatric

Association, is estimated to affect 6% of the American population. Another 25 million Americans may have a mild form of SAD, sometimes called the "winter blues" or "winter blahs." The risk of SAD increases the further from the equator a person lives; one early study of SAD found a 1.4% incidence of the disorder among people living in Florida, compared with 9.7% among residents of New Hampshire. Other factors that influence the incidence and severity of SAD are sex and age. Women are more likely than men to develop SAD, but men with the disorder are more severely depressed than most women who have it. SAD appears to decrease in severity with age; the elderly have milder SAD symptoms than adolescents.

Comparative studies indicate that the incidence of SAD in the United States and Canada is about twice as high as in European countries at the same latitudes north of the Equator. These findings suggest that cultural factors are also involved in the disorder.

The symptoms of SAD are similar to those of other forms of depression. People with SAD may feel sad, irritable, or tired, and may find themselves sleeping too much. They may also lose interest in normal or pleasurable activities (including sex), become withdrawn, crave carbohydrates, and gain weight.

Content licensed from:

Author Info: Paula Ford-Martin, Rebecca J. Frey PhD, The Gale Group Inc., Gale, Detroit, Gale Encyclopedia of Alternative Medicine, 2005

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