As sunlight has affected the seasonal activities of, SAD may be an effect of this seasonal light variation in humans. As seasons change, there is a shift in our “biological internal clocks” or circadian rhythm, due partly to these changes in sunlight patterns. This can cause our biological clocks to be out of “step” with our daily schedules. The most difficult months for SAD sufferers are January and February, and younger persons and women are at higher risk.

Symptoms Include:

• regularly occurring symptoms of depression (excessive eating and sleeping, weight gain) during the fall or winter months.
• full remission from depression occur in the spring and summer months.
• symptoms have occurred in the past two years, with no nonseasonal depression episodes.
• seasonal episodes substantially outnumber nonseasonal depression episodes.
• a craving for sugary and/or starchy foods.

Possible Cause of this Disorder
Melatonin, a sleep-related hormone secreted by the pineal gland in the brain, has been linked to SAD. This hormone, which may cause symptoms of depression, is produced at increased levels in the dark. Therefore, when the days are shorter and darker the production of this hormone increases.

Treatments
Phototherapy or bright light therapy has been shown to suppress the brain’s secretion of melatonin. Although, there have been no research findings to definitely link this therapy with an antidepressant effect, many people respond to this treatment. The device most often used today is a bank of white fluorescent lights on a metal reflector and shield with a plastic screen. For mild symptoms, spending time outdoors during the day or arranging homes and workplaces to receive more sunlight may be helpful. One study found that an hour’s walk in winter sunlight was as effective as two and a half hours under bright artificial light.