People with SAD suffer from the symptoms of depression during the winter months. People who live in northern latitudes or in cloudy, rainy climates suffer from this illness much more frequently than do people who live in warm, sunny climates. SAD is also very prevalent in Maine and Canada. SAD is believed to result from an increase in the neurotransmitter melatonin. Levels of melatonin increase as we sleep.
Light suppresses melatonin production.
The pineal gland in the brain releases melatonin. Symptoms often first appear in late October when we set the clocks back an hour. That's another hour of light lost. These side effects may occur as a result of sitting in front of a light box for too long or sitting too close to the light box. Melatonin production, which has built up over the course of the night while we're sleeping, is suppressed.