Although there was a time around the turn of the century when sunlight was believed to be a cure for everything from menstrual cramps to baldness, Dr. Daniel F. Kripke, who has been encouraged by his experiments with nighttime phototherapy on severely depressed patients at the Veterans Administration Hospital in San Diego, says legitimate use of light therapy is "just now in its infancy. But we think it's going to prove to be a very useful tool."
Like other experts in the field, Dr. Kripke still does not know why light triggers a chemical reaction in the body. One theory—laughed at by some, embraced by others—is that humans tend to go into a sort of prehibernating phase during the dark months. This would explain the SAD symptoms of weight gain, the need for 10-14 hours of sleep, lethargy and a craving for carbohydrates.
"It's been looked at as a preparatory state for winter, not quite hibernation but something close," says Dr. David Avery, a psychiatrist at Harborview Medical Center in Seattle. However, recent research casts some doubt on the hibernation theory.
All that the researchers seem willing to agree on is that light, entering the body through the optic nerves, somehow cures, or at least lessens, winter depression. Many humans simply can't live in the dark without getting cabin fever—which is a less scientific, but essentially accurate, description of SAD.
If you work indoors in typical light, don't get out much for lunch or other long breaks, and live in a city north of the 40th parallel—a line approximately between Philadelphia and Reno—where there is less than 10 hours of sunlight a day in December, you are probably light-starved in winter, although that doesn't necessarily mean you will become depressed.
The sunlight measured at a window on a typical clear summer day is 2,500 lux; on a cloudy day, it's about 1,000 lux. But an average home or office is lit with a mere 500 lux. In Fairbanks, Alaska, where Dr. Carla Hellekson has found widespread cases of SAD beginning as early as September, a winter day may bring less than four hours of natural light, some of it registering as low as 60 lux.
For those who can't afford a sojourn in Palm Springs or seasonal sessions with a shrink, the experts say one can chase the winter blues a long way by getting outdoors every day. Early morning is an especially good time. But doctors warn that seasonally depressed people should not expect to be able to treat themselves with normal lighting.
What does help, according to Dr. Hellekson and others, is to sit near a south-facing skylight in the home or office, so that one can "take the sun," as the Victorians used to advise. Another suggestion is to go skiing—cross-country or downhill—since a bright winter day on snow provides almost as much light as a summer outing.
There's even hope for Sunday afternoon football-or basketball-watching couch potatoes: A mere 30 minutes a day of strong light may be enough to counter lethargy. Just by spending half-time outside, you may have something to cheer about.