It's more common in the young than in the elderly. People who have SAD typically have it for decades, but they learn to live with it. "You can go south in winter if it's a major problem," he said.

Reimherr said the gray of winter doesn't just affect those with SAD. In careful long-term studies of depression, researchers have documented an increase in depressive illness in winter.

He suggests people make it a point to get up out of the fog and have some fun. There's nothing quite like skiing in the clear, bright air, he said. He likes to escape winter gray days by hiking in southern Utah, too.

But although exercise can improve both mental and physical health, there's some danger involved in exercising outdoors on polluted days. Health officials counsel against outdoor exertion when pollution levels are high. And a number of studies, including two by Brigham Young University epidemiologist Arden Pope, indicate that the small-particulate pollution that's hanging around the Wasatch Front these days can contribute not only to respiratory disease, but to heart disease, as well.

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E-mail: lois@desnews.com