SAD: Season Affective Disorder
It’s that time of the year again, a time when light is more scarce and darkness is abundant. Seasonal Affective Disorder, SAD for short, affects from 1.4 percent (in Florida) to 9.7 (in New Hampshire) this time of year, according to epidemiological studies. There are obvious similarities between the behavior seen in humans during the winter months and other mammals. In mammals during the dark months, burrowing, sluggishness, and excessive sleep is common. These traits contribute to the survival of mammals during the winter months. Many scientists theorize that SAD may be related to innate survival traits similarly found in humans. Exposure to industrial light may be a factor that reduces the prevalence of SAD. Additionally, artificial light in the morning may help to reduce nocturnal melatonin secretion, which contributes to SAD. The following is an excerpt of an article from the New York Times that discusses issues surrounding SAD:
In 2001, Dr. Thomas A. Wehr and Dr. Norman E. Rosenthal, psychiatrists at the National Institute of Mental Health, ran an intriguing experiment. They studied two patient groups for 24 hours in winter and summer, one group with seasonal depression and one without.
A major biological signal tracking seasonal sunlight changes is melatonin, a brain chemical turned on by darkness and off by light. Dr. Wehr and Dr. Rosenthal found that the patients with seasonal depression had a longer duration of nocturnal melatonin secretion in the winter than in the summer, just as with other mammals with seasonal behavior.
Why did the normal patients show no seasonal change in melatonin secretion? One possibility is exposure to industrial light, which can suppress melatonin. Perhaps by keeping artificial light constant during the year, we can suppress the “natural” variation in melatonin experienced by SAD patients.
There might have been a survival advantage, a few hundred thousand years back, to slowing down and conserving energy — sleeping and eating more — in winter. Could people with seasonal depression be the unlucky descendants of those well-adapted hominids?
Regardless, no one with SAD has to wait for spring and summer to feel better. “Bright light in the early morning is a powerful, fast and effective treatment for seasonal depression,” said Dr. Rosenthal, now a professor of clinical psychiatry at the Georgetown Medical School and author of “Winter Blues” (Guilford, 1998). “Light is a nutrient of sorts for these patients.