What is seasonal depression?

Seasonal Affective Disorder (SAD) is a subtype of depression with a clear seasonal pattern. In the Northern Hemisphere, depressive episodes typically begin in fall-winter and lift in spring-summer; in the Southern Hemisphere, the same pattern is reversed.

Symptoms specific to SAD (a bit different from typical depression): hypersomnia (sleeping excessively), intense carbohydrate cravings and increased appetite, weight gain, marked lethargy, and low mood, on top of the usual symptoms of depression.

Main cause: reduced sunlight during shorter days. This disrupts the circadian rhythm and can lower serotonin while increasing melatonin production, triggering depressive symptoms in vulnerable people.

Treatment: light therapy (exposure to high-intensity artificial light, 10,000 lux, for 20-30 minutes in the morning) is the first-line treatment, with effectiveness comparable to antidepressants for SAD. Antidepressants (SSRIs) are also effective. Combining the two works well for more severe cases.

Who is affected: SAD is more common in places farther from the equator, where daylight varies more across the year; it is less common close to the equator or in tropical regions with little seasonal light variation.