Does wintertime get you down? With darker days and longer nights, do you yearn to just stay in bed? Are you moodier, less focused, and more irritable this time of year? You could be suffering from seasonal affective disorder, appropriately abbreviated SAD.

Many people report that seasons affect their moods. Depression tends to be highest in the winter and lowest in the summer. Feelings of anger, hostility, irritability, and anxiety also occur more in the winter, surveys show. For an estimated 10 million Americans, this is diagnosed as pure SAD. Another 25 million may have a milder form of the disorder.

Up to 80 percent of SAD sufferers are women, most of whom start experiencing symptoms in young adulthood. While the causes aren't well understood, a gene has recently been identified that may make people prone to SAD by affecting their response to light. The reduction in light during the wintertime appears to cause SAD in susceptible people by disturbing the body's natural clock. In fact, people with SAD have a feeling of continual jet lag. But this offers a way to treat the condition: intense artificial light can actually reset the body's internal clock and ease symptoms. Researchers believe this works by boosting the body's level of serotonin, a hormone that is associated with wakefulness and mood.

"Bright lights have been shown to help some people with seasonal depression," said Marguerite M. Blythe, M.D., a psychiatrist with the Health Alliance. "Antidepressent medications can also help, and some people feel that moving to a latitude with longer days and less cloud cover has helped."

Exercise, psychotherapy and phototherapy also are beneficial. Lamps emitting light close to the natural frequency of the sun are available. They should be used everyday for 30-60 minutes. For more information on these devices, contact the Winter Blues Information Network at 888-SAD-AWAY or your health care provider. To find a physician near you visit our "find a physician" page (link) or call 1-888-749-DrDr (3737).