What is seasonal affective disorder?

Seasonal affective disorder (also called SAD) is a kind of depression that follows the seasons. The most common type of SAD is called winter depression. It usually begins in late fall or early winter and goes away by summer.

A less common type of SAD, known as summer depression, begins in the late spring or early summer. SAD may be related to changes in the amount of daylight we get.

Do many people get SAD?

About 4 to 6 percent of people may have winter depression. Another 10 to 20 percent may have mild SAD. SAD is four times more common in women than in men. Although some children and teenagers get SAD, it usually doesn't start in people younger than age 20. Your chance of getting SAD goes down as you get older.

SAD is also more common the farther north you go. For example, it's seven times more common in Washington state than in Florida.

How does my doctor know I have SAD?

Your symptoms are clues to the diagnosis. Not everyone with SAD has the same symptoms, but common symptoms of winter depression include the following:

• A change in appetite, especially a craving for sweet or starchy foods

• Weight gain

• A heavy feeling in the arms or legs

• A drop in energy level

• Fatigue

• A tendency to oversleep

• Difficulty concentrating

• Irritability

• Increased sensitivity to social rejection

• Avoidance of social situations—not wanting to go out

Symptoms of the summer version of SAD are poor appetite, weight loss and insomnia. Either type of SAD may also include some of the symptoms that are present in other kinds of depression, such as feelings of guilt, a loss of interest or pleasure in activities you used to enjoy, feelings of hopelessness or helplessness, or physical problems such as headaches and stomachaches.

Symptoms of SAD keep coming back and tend to come and go at about the same time every year. The changes in mood are not necessarily related to obvious seasonal problems (like being regularly unemployed during the winter).

Is there a treatment for SAD?

Yes. Winter depression is probably caused by a lack of sunlight. So, light therapy is one way to treat winter depression.

If your doctor suggests that you try light therapy, you will use a special light box or a light visor that you wear on your head like a cap. You will sit in front of the light box or wear the light visor each day. Generally, light therapy takes about 30 minutes a day in the fall and winter, when you're most likely to be depressed. If light therapy helps you, you'll keep using it until more sun is available in the springtime. Stopping light therapy too soon can make the symptoms come back.

When used properly, light therapy seems to have few side effects. Side effects include eye strain, headache, fatigue, irritability and inability to sleep. This happens if light therapy is used late in the day.

Tanning beds shouldn't be used to treat SAD. The light sources in tanning beds are high in ultraviolet (UV) rays, which harm your eyes and your skin.

If you have SAD, your doctor may also want you to try a medicine or behavior therapy. If light therapy or medicine alone doesn't work, your doctor may want you to use them together.