Seasonal affective disorder (SAD) is a type of depression. It happens during certain seasons of the year, most often fall or winter. It is thought that shorter days and less daylight may set off a chemical change in the brain leading to symptoms of depression.

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Who is at risk for SAD?

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SAD often starts during adulthood. The risk of SAD increases with age. It’s rare in people younger than age 20. Women are affected more often than men.

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What causes SAD?

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Less sunlight and shorter days are thought to be linked to a chemical change in the brain. They may be part of the cause of SAD.

Melatonin, a sleep-related hormone, also has been linked to SAD. The body naturally makes more melatonin when it’s dark. So when the days are shorter and darker, more melatonin is made.

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