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. 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.