Boston , MA —As winter approaches, some will begin to feel sluggish and gloomy. Winter depression accounts for about 10% of cases of major depression. The November issue of the Harvard Mental Health Letter examines this condition, referred to as seasonal affective disorder, and explores whether a little bright light can alter this dark mood.

Seasonal affective disorder (SAD) is defined as depression that occurs repeatedly at the same time of year, usually starting in the fall and ending in the spring. People with SAD are sad, tired, anxious, irritable, unable to concentrate, and inclined to avoid friends and social activities. But often they have physical symptoms as well, such as overeating and excessive sleep. Studies suggest that SAD runs in families. Additionally, seasonal depression is thought to be more common and longer lasting at high latitudes, so it appears to also stem from changes in the length of the day.

Sunlight has always been regarded as an antidote to lethargy and gloom. Bright light treatment for SAD involves mounting fluorescent lights on a metal reflector, with a plastic screen that filters out damaging ultraviolet frequencies and diffuses the light to prevent glare. The patient sits near this apparatus for a half-hour to two hours a day. Experts usually recommend 10,000 lux, which is about the equivalent to early morning sunlight. Improvement begins in a few days and treatment continues throughout the winter. There are a few side effects, mainly occasional headaches or eyestrain.

For milder seasonal mood changes, the November issue recommends adding more lamps, sitting near windows, or spending more time outdoors. One study found that an hour's walk in winter sunlight was as effective as 2 ½ hours of artificial light. Other treatment approaches include the use of antidepressant drugs and the herb St. John's wort. People with SAD may also benefit from cognitive behavioral therapy.