About This Condition
Seasonal affective disorder (SAD) is an extreme form of common seasonal mood cycles, in which depression develops during the winter months.
How seasonal changes cause depression is unknown, but most of the research into mechanisms and treatment has focused on changes in levels of the brain chemicals melatonin and serotonin in response to changing exposure to light and darkness.
SAD is characterized by typical symptoms of depression, such as sadness, hopelessness, and thoughts of suicide (in some cases), and “atypical” depressive symptoms such as excessive sleep, lethargy, carbohydrate cravings, overeating, and weight gain. The symptoms usually occur the same time of year, typically fall and winter, and disappear with the onset of spring and summer.
Light exposure research and treatment measures in “lux” units. For example, the intensity of light on a high mountain at the equator at midday is greater than 100,000 lux, compared with less than 11 lux generated by a moonlit night. A well-lit kitchen or office may be around 500 lux.
Treatment includes daily exposure to bright light, often 2,500 lux administered in two-hour increments. Individuals with SAD should spend as much time as possible outside during the day. Use of a “dawn simulator,” a light programmed to slowly increase in intensity in the morning, is also recommended. Some healthcare providers might also recommend aerobic exercise under bright lights.