It's still not understood why women develop SAD at three times the rate of men, but Rosenthal says it may be related to an increase in reproductive hormones. Symptoms tend to first appear in women who suffer from SAD soon after a girl begins to menstruate. While SAD symptoms can reappear winter after winter, they tend to decline or largely disappear in women after menopause. As women age, he said, "the preponderance of SAD becomes more equal between men and women." One theory is that SAD may be somehow related to the seasonal hormonal changes that gear animals to reproduce during the time of year when their offspring are most likely to survive. "Light is believed to play a role in evolution as a mechanism for controlling reproductive function," Rosenthal said. "It may be that in certain people a primitive mechanism is unleashed that is not overridden by today's artificial light."

There are also indications that the condition is more common in some ethnic and racial groups than others. "Icelandic people tend to have much lower levels of it," Rosenthal said. "The same is true of Asians, including the Japanese and Chinese." It's possible that some groups adapted better than others, he said, but it may also be that those who were made the most miserable by long, dark days were motivated to move to sunnier climates.

Like other forms of depression, SAD runs the gamut from mild to severe cases, but Rosenthal says no one has to wait until the disorder becomes debilitating to take action. Some people need a combination of treatments, like antidepressants and cognitive behavior therapy, to feel better. But alternatives, like increased exposure to light, more exercise, stress-reduction strategies and changes in diet (less carbs, more protein, à la the South Beach or Atkins diets) can also make a big difference. Specially designed "light boxes" that simulate the brightness of the outdoors on a sunny day can help, as can light visors that can be worn like a hat. Check with a clinician to determine the appropriate "dose" and timing of light therapy so that symptoms decrease but the therapy doesn't affect your ability to fall asleep at night. Traveling to sunnier climes for the winter also helps, Rosenthal said. (Tanning beds, however, are not recommended.)

Rosenthal said he has learned to reduce his own symptoms by sticking to a disciplined regime from October to April. He has a light box that turns itself on each morning and gradually brightens, until it floods his bedroom with simulated daylight. He has also become a big fan of brisk morning walks. Not only is it a good way to get vigorous exercise, but even on a gloomy day the outdoors is much brighter (and mood-lifting) than an artificially lit interior. Over time, he says, he has learned to appreciate the change of season. "I even enjoy ice storms and dark, dreary days," he said. Maybe for him, but a prescription for a month in the Caribbean sounds better to us.

© 2007