As fall transitions to winter, the weather cools in much of the country and the days grow shorter and darker. Many people find that their mood darkens along with the days. They feel sad and hopeless, want to do little more than sleep, and barely have enough energy to get through their days. People who feel down during the winter months have a condition known as seasonal affective disorder, or SAD.

Seasonal affective disorder isn?t the same as the ?winter blues,? a mild feeling of sadness that coincides with the winter months. It?s a real medical diagnosis, with symptoms that are severe enough to affect a person?s day-to-day life. Seasonal affective disorder is more common in northern climates than in southern climates. Women are more likely than men to have this condition, particularly if they have family members with seasonal affective disorder or depression.

Experts don?t know exactly what makes some people depressed during the winter months. They suspect seasonal affective disorder stems from a disruption to the body?s internal clock, called the circadian rhythm. Shorter days interrupt the production of melatonin, a natural chemical that helps us fall asleep.

Even though seasonal affective disorder typically lasts only as long as the season, it does need to be treated. Like other forms of depression, it can get worse over time, and can even lead to suicidal thoughts or actions.

One way to relieve sadness during the winter is with light therapy. Patients sit in front of a light box every morning for about 30 minutes. The light exposure can help reset circadian rhythms, and relieve symptoms of seasonal affective disorder. For some people, light therapy isn?t enough. They also need talk therapy to combat the negative thoughts that are preoccupying their mind.