Seasonal affective disorder is a mental health condition that is triggered by the changing of the seasons. This condition is a subtype of major depressive disorder and bipolar disorder. Major depressive disorder is characterized by prolonged sadness and a general lack of interest, while bipolar disorder is characterized by similar depressive episodes alternating with periods of abnormally high energy and activity (hypomania or mania). People with seasonal affective disorder have signs and symptoms of either major depressive disorder or bipolar disorder only during certain months of the year. Major depressive disorder is more common than bipolar disorder among people with seasonal affective disorder. This condition usually begins in a person's twenties or thirties.

The causes of seasonal affective disorder are complex. A shortage of sunlight contributes to the development of the disorder in the fall and winter months, and too much sunlight is associated with seasonal affective disorder in the spring and summer months. Affected individuals seem to have disrupted daily (circadian) rhythms, such as the sleep-wake cycle, which are normally regulated to match the night-day cycle. These individuals cannot alter their sleep-wake cycle to match the night-day cycle of the winter months, resulting in changes in sleep, mood, and behavior. Those with seasonal affective disorder in summer have difficulty adjusting to the increased daylight hours. It is likely that affected individuals are genetically predisposed to being unable to adjust their circadian rhythms. Studies have identified variants in multiple genes that are associated with developing seasonal affective disorder. However, few of these variants have been verified in multiple studies.

Seasonal affective disorder occurs in 0.5 to 3 percent of individuals in the general population; it affects 10 to 20 percent of people with major depressive disorder and about 25 percent of people with bipolar disorder.

Seasonal affective disorder does not have a clear pattern of inheritance in families. Overall, the risk of developing this condition is greater for first-degree relatives (such as parents or siblings) of affected individuals compared to the general public. Studies have found that approximately 15 percent of individuals with seasonal affective disorder have a first-degree relative who also has the condition.

Published Date: May 01, 2019
Published By: National Institutes of Health