seasonal affective disorder (SAD) /sē″zənəl/ , a mood disorder associated with the shorter days and longer nights of autumn and winter. Symptoms include lethargy, depression, social withdrawal, and work difficulties. The patients also consume excess amounts of carbohydrates, gaining weight. The symptoms recede in the spring, when days become longer. The condition is associated with the effect of light on melatonin secretion and is treated with light therapy for 5 to 6 hours per day.
