Seasonal Affective Disorder is responsible for unexplained bouts of depression and fatigue during the winter months in many. Researchers believe that the lack of sunlight during the winter months is responsible for the SAD phenomenon. One theory states that during seasons of lowered light the body produces more melatonin, which in turn can cause depression. SAD seemingly affects a higher rate of women than men and is seven times more prevalent in northern latitudes. The following is an excerpt of an article that discusses seasonal affective disorder:
Each winter as the days become shorter, millions of Americans are affected by unexplained bouts of depression and fatigue. More than the winter blahs, seasonal affective disorder (SAD) is a serious form of depression that can disrupt a person’s life from fall until spring.
Researchers are unsure of the exact cause of SAD; however, it appears to be triggered by a lack of sunlight. One theory maintains that decreased daylight interferes with the circadian rhythms that regulate the body’s internal clock. Another possible cause may be increased levels of the sleep-related hormone melatonin. When days have fewer hours of sunlight, the body produces higher levels of melatonin, which may cause symptoms of depression.