What is seasonal affective disorder?

Seasonal affective disorder (also called SAD) is a type 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, usually begins in the late spring or early summer. SAD may be related to changes in the amount of daylight.

Do many people get SAD?

Surveys estimate that four to six of every 100 people may have winter depression, and another 10% to 20% 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 20. The risk of SAD decreases as you get older. SAD is 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?

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

Symptoms of the summer depression 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, ongoing feelings of hopelessness or helplessness, or physical problems such as headaches and stomach aches.

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 stressors (like being regularly unemployed during the winter).

Is there a treatment for SAD?

Summer depression may be similar to other kinds of nonseasonal depression, but winter depression is probably caused by a reaction to a lack of sunlight. This theory has led to the development of light therapy for the treatment of winter depression.

If your doctor suggests you try light therapy, you will use a specially made desk-type 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 for a certain length of time each day. Generally, light therapy takes about 30 minutes each day throughout the fall and winter, when you're most likely to be depressed. If light therapy helps you, you'll continue using it until enough daylight is available, typically in the springtime. Stopping light therapy too soon can make the symptoms come back.

When used properly, light therapy seems to have very few side effects. Side effects include eye strain, headache, fatigue, irritability and inability to sleep (if light therapy is used too late in the day). Caution is required with light therapy in people with manic depressive disorders, skin that is sensitive to light, or medical conditions that make their eyes vulnerable to light damage.

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