Seasonal Affective Disorder (SAD)

Seasonal Affective Disorder (SAD) is a subtype of depression with a seasonal pattern: recurring depressive episodes that begin and end at specific times of year, most often in fall/winter (when there is less daylight), remitting in spring/summer.

Classic symptoms include: hypersomnia (sleeping excessively), hyperphagia (eating more, especially carbohydrates), weight gain, lethargy, depressed mood, social withdrawal, and difficulty concentrating. It differs slightly from classic MDD — hypersomnia and hyperphagia are more common than insomnia and appetite loss.

The mechanism involves changes in circadian rhythms and in the melatonin and serotonin systems in response to reduced sunlight. Prevalence varies with latitude: it is more common in regions farther from the equator with greater seasonal swings in daylight (Nordic countries, northern parts of the US and Canada, the UK) and less common closer to the equator — but it occurs everywhere, especially in people who are particularly sensitive to changes in light.

Treatment includes light therapy (exposure to high-intensity artificial light in the morning), CBT adapted for SAD, and SSRIs when needed.