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Seasonal depression, or seasonal affective disorder (SAD), is a depression that occurs each year at the same time, usually starting in fall or winter and ending in spring or early summer. People who experience SAD have many of the common signs of depression including sadness, anxiety, irritability, loss of interest, social withdrawal, and difficulty concentrating. This can be accompanied by extreme fatigue, increased need for sleep, craving for carbohydrates, and increased appetite and weight gain.
Between 4%-6% of the U.S. population experiences SAD. Three-quarters of those with SAD are women, with symptoms often beginning in their early 20's. This disorder can also occur in children and adolescents. Older adults are less likely to experience SAD.
While the exact cause of this condition is not known, the greater incidence of SAD in people who live further north geographically strongly suggests that it is caused by changes in the availability of sunlight. One theory is that with decreased exposure to sunlight, the biological clock that regulates mood, sleep, and hormones is delayed, running more slowly in winter. Another theory is that brain chemicals that transmit information between nerves, called neurotransmitters (such as serotonin), may be altered in individuals with SAD. It is believed that exposure to light can correct both of these types of imbalances.
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Content last modified on Jun 10, 2005
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