Seasonal Affective Disorder: Symptoms, Causes, Treatment

Diagnosis considers depressive episodes linked to seasons and improvement at other times, not feeling low on one rainy day. Assessment also considers nonseasonal depression and bipolar disorder.

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Low mood, reduced interest, low energy and poor concentration may occur. Oversleeping and increased appetite are more typical in winter, while insomnia and reduced appetite may occur in summer. Not every feature is necessary.

The cause is not fully understood. Light exposure, body-clock changes, sleep and mood regulation may interact with individual susceptibility. A low vitamin D result does not establish the sole cause of depression.

Personal or family mood-disorder history and environments with substantial seasonal light variation may increase risk. SAD is not restricted to people living in very cold countries.

Assessment reviews duration, impact, seasonal recurrence, medicines and possible medical mimics, including episodes of unusually high energy or reduced need for sleep. No single blood test diagnoses SAD.

Options include psychological therapy, antidepressants and appropriately selected light therapy for winter-pattern illness. Light-box selection and timing need care, especially with eye disease or photosensitizing medicines. Evidence for vitamin D alone is mixed and it does not replace appropriate care.

Daily functioning, relationships and self-care may suffer, and substance use or suicidal thinking may coexist. Treatment matters even when symptoms are expected to improve with seasonal change.

Regular sleep, activity, daylight exposure and social contact can support treatment. People with recurrent episodes can plan with clinicians before the relevant season. Do not independently start or stop prescribed medicines.