Seasonal Affective DisorderSeasonal affect disorder might be diagnosed when someone has depressive symptoms during the winter season. Symptoms can include a lack of motivation to do normal activities or engage socially, as well as fatigue and weight gain.
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Symptoms of depression that take place during the winter months may be a sign of seasonal affective disorder. Typically, mood changes begin in the fall and continue until the spring. In rare cases, seasonal affective disorder starts in the late spring and lasts throughout the summer.
Although the cause of seasonal affective disorder is unknown, some evidence suggests that the changes in mood are related to reduced exposure to natural sunlight. For instance, the body relies on sunlight and other external cues to reset its biological clock. Seasonal changes can disrupt this pattern as well as cause a drop in levels of serotonin, the neurotransmitter that helps regulate mood.
Seasonal affective disorder is more common in women, people living in regions with relatively little sunlight year-round and those with relatives who have also been affected.