Seasonal Affective Disorder (SAD) is a pattern, experienced by about 15 percent of people diagnosed with depression, in which depressive symptoms occur as a function of the calendar. In SAD a period of severe depression, accompanied by irritability and excessive sleeping, coincides with the months of shorter daylight that occur in winter. For obvious reasons, the disorder is far more common in temperate zones than in tropical areas. The depression tends to lift as daylight hours grow longer with the approach of spring, suggesting that disruptions in the body’s circadian rhythms are responsible. For a diagnosis of SAD to be made, there should therefore be a full remission from depressed symptoms during the spring and summer months. Though poets have noted the debilitating effects of winter’s darkness for centuries, and researchers have long puzzled over the high suicide rates in countries near the Arctic Circle, the disorder was only formally described and given its current name in the 1980s.
The body’s internal clock is largely governed by the secretion of melatonin, a hormone, by the pineal gland. Melatonin is involved in governing our wake/ sleep cycle and overall levels of arousal in the brain. Higher levels of melatonin are associated with reduced arousal and increased lethargy, which is why melatonin is sometimes sold as a sleep aid. The pineal gland’s location near the optic chiasm, where the optic nerves, coming directly from the eyes, cross over each other, allows the secretion of melatonin to be governed by ambient light levels, and so more melatonin is released in periods with less sunlight. Since melatonin levels inﬂuence the levels of such neurotransmitters as norepinephrine, serotonin, and dopamine, all of which are known to be involved in depression, it follows that in certain individuals, the absence of sunlight may lead to neurotransmitter level changes sufﬁcient to cause depression.
The standard treatment for SAD, phototherapy, has a fairly short history. In phototherapy the individual is exposed daily to bright, full-spectrum light for anywhere from half an hour to several hours. Usually this exposure comes in the form of a specially constructed light box, which contains several ﬂuorescent tubes and a reﬂector to help focus the light, though research suggests that a half-hour walk outdoors in winter sunlight may be as helpful as two hours with an indoor light box. As with all psychotherapy, compliance can be a problem, especially in a disorder for which difﬁculty getting up in the morning is a deﬁning symptom. It is therefore fairly common for light boxes to be set up as dawn simulators, coming on in the early morning according to a timer and gradually increasing in brightness so that they reach full intensity at the time the person wishes to awaken.
- Faedda, G., Tondo, L., Teicher, M., Baldessarini, R., Gelbard, H., and Floris, G. “Seasonal Mood Disorders: Patterns of Seasonal Recurrence in Mania and Depression.” Archives of General Psychiatry, 50 (1993): 17–23.