Seasonal affective disorder (SAD) is a form of depression that occurs in the fall and winter months, probably in response to the shorter hours of daylight. No one knows exactly what causes SAD, but we do know that it is rare close to the equator and becomes more common the farther away from it you live. Symptoms are typical of depression: fatigue, lack of interest in normal activities, social withdrawal, weight gain, and a craving for carbohydrate foods. However, some of these symptoms occur with other disorders including hypothyroidism (low thyroid function), hypoglycemia, infectious mononucleosis and other viral infections. If you think that you have SAD, I suggest consulting your physician to make sure that your symptoms aren’t due to something else.
Exposure to bright light daily is the treatment method most often recommended for patients whose SAD symptoms are severe enough to affect their daily lives. You need a special (full-spectrum) light source. Typically, SAD patients must sit in front of the light for about a half an hour per day. This type of light therapy is reputed to work in 80 percent of all cases, but a new study from the University of Vermont suggests that cognitive behavior therapy (CBT) is very effective at preventing recurrences of SAD, perhaps even more so than light therapy or a combination of light therapy and CBT. What’s more, CBT proved effective after only a few weeks, whereas light therapy must be continued through the winter season.
For milder cases of SAD, a long daily walk outdoors or arranging your home or office so that you’re exposed to a window during the day can also work, according to the American Psychiatric Association. And daily aerobic exercise is still the most effective treatment I know of for mild to moderate depression.
Some research suggests that a vitamin D deficiency might underlie SAD and that supplementing with vitamin D might help. Since it is estimated that more than 70 percent of the U.S. population is D-deficient, I recommend that everyone take a daily supplement of 2,000 IU. Higher doses of D may be needed to effectively treat SAD.
Andrew Weil, M.D.