Come the dark days of winter, everyone can feel a bit down from time to time.

But for millions, these shorter, colder days bring on seasonal affective disorder (SAD), a condition characterized by depression, social withdrawal, overeating and weight gain.

"It's a fairly large problem," said Randall Flory, a SAD researcher at Hollins University in Roanoke, Va. "It's estimated that in the U.S. about 6 to 7 percent of people have a pretty severe form of SAD."

Luckily, the best therapy so far for SAD may also be one of the safest -- light.

In a five-year study that was the first of its kind, Randall found that daily light box therapy consistently outperformed antidepressant drug therapy or air ionizers as the best remedy for the seasonal condition.

"We estimate that 80 percent of people affected will find benefit from [exposure to] bright light," said Flory, who first presented his findings at the 2003 annual meeting of the American Psychological Association.

Individuals with SAD tend to dread the onset of winter, said Anie Kalayjian, a professor of psychology at Fordham University in New York City, and a spokeswoman for the American Psychological Association.

"They have real difficulty motivating themselves to do ordinary things, even taking care of themselves and those they are responsible for," she said. As winter sets in and deepens, SAD sufferers tend to retreat into activities such as sleeping (often three to four hours longer per day than in the summer months) and overeating, with rapid weight gain.

No one is quite sure what causes SAD, although the fact that women are four times more likely to report the condition than men points to hormonal causes. However, men may simply be underreporting their true incidence of SAD, Kalayjian said.

"Women tend to express themselves more -- they don't have the societal hang-ups that say 'Oh, I can't talk about this,'" she said. "Men tend to rely more on things like drinking, or they become aggressive, or cover it up."

Kalayjian said she's also seeing more and more children with SAD in her practice. "There was a recent study that found that 3 to 5 percent of children have the disorder."

In his study, Flory's team observed the progress of 140 women with SAD over four consecutive winters. The researchers compared the effectiveness of two popular non-pharmaceutical treatments: 30 minutes per day of exposure to a box emitting powerful UV light; and air-cleaning devices that increase airborne levels of negatively charged ion. Scientists believe wintertime changes in the ionization of air may play some role in SAD.

The light boxes were the clear winner in terms of long-term symptom reduction, Flory reported, although the ionizers did have some ameliorative effect. According to Flory, this suggests that SAD is caused by a combination of environmental factors, including reduced wintertime light and changes in air ionization.

Both Flory and Kalayjian said they avoid treating SAD with antidepressant drugs whenever possible. One reason is price -- while buying a light box costs a patient about $60 a year over four years, the annual cost of an SSRI antidepressant such as Prozac or Zoloft can easily top $300 annually, Flory said.

"Some people with very, very severe SAD do use SSRIs," Kalayjian said, "but I would really encourage patients to look at preventive ways -- knowing your body and mind, and working with them."

Besides heightened exposure to light, Kalayjian has a few more tips she's seen work with SAD patients:

• Follow the sun. Kalayjian suggests that people with SAD rethink their vacation calendars. "You might want to take a bit of vacation somewhere south in the winter, rather than traveling only during the summer months," she said.
• Get active. Exercising first thing in the morning "helps tremendously," Kalayjian said, energizing the body as it helps banish the winter blues.
• Meditate. "Certain techniques, such as tensing a muscle for 10 seconds, then letting it go, seem to invigorate the body," she said.
• Express yourself. Research suggests that SAD lessens its grip on individuals who communicate their feelings more openly. Even keeping a daily journal can help, Kalayjian said.

More information

To learn more about SAD, visit the National Mental Health Association.