Biological Cause for Winter Blues

There may be a biological explanation for people who suffer from depression during the winter, according to a study.
Seasonal Affective Disorder is a common ailment resulting in depression during the winter. Symptoms often include weight gain, increased sleep and decreased activity. People with SAD often respond to treatment with bright light.

Researchers with the National Institute of Mental Health have found individuals with SAD produced more melatonin during the winter than during the summer. Healthy patients had no seasonal change in melatonin levels, leading researchers to believe melatonin production is a biological signal of seasonal change in SAD patients. Melatonin is a hormone secreted in the brain that regulates the body’s internal clock.

The study measured 110 participants, 55 with SAD and 55 volunteers without the condition, for melatonin levels during both the summer and winter. Patients with SAD produced melatonin for an average of 9 hours during the winter but only 8.4 hours during the summer. The control group had no seasonal change in melatonin levels.

This is the first study to demonstrate that humans, much like other mammals, generate a biological signal of changing seasons.