What is seasonal affective disorder (SAD)?
If you are depressed during the shorter days of winter but feel happier and more energetic in spring and summer, you may have seasonal affective disorder (SAD). SAD is a type of depression that affects you at the same time each year, usually in the fall or winter. But as the days lengthen in spring and summer, the depression lifts.

What causes SAD?
Shorter days of winter and lack of light are considered one cause of seasonal depression, especially for people who move to extreme northern climates, where winter days are very short or seasonal differences in the amount of daylight are extreme.1, 2 However, researchers are studying other possible causes, including disturbances in the body's natural biological clock (circadian rhythms) or problems with the regulation of a brain chemical (neurotransmitter) called serotonin.

What are the symptoms?
Symptoms of SAD include irritability, sadness, anxiety, increased appetite and a craving for carbohydrate, weight gain, decreased activity and a need for more sleep, drowsiness during the daytime, and problems with work and relationships.

Symptoms begin and end around the same time each year for each person, usually starting in September or October and ending in April or May.

How is SAD diagnosed?
A doctor will base his or her diagnosis of SAD on whether you have been depressed in the winter and recovered in the spring or summer for at least 2 years in a row. These dramatic mood swings in response to changes in seasons are what differentiate SAD from nonseasonal depression.

Although many of the symptoms for depression and SAD are the same, your doctor will look for increased appetite (especially cravings for carbohydrate), weight gain, and excessive sleeping as symptoms that help diagnose whether you have seasonal depression. Your doctor may also ask if a close relative-a parent or sibling-had seasonal depression.

How is it treated?
Treatment for SAD includes light therapy, in which you sit at a certain distance from artificial bright lights, usually in the morning. Another form of light therapy called dawn simulation is also used. With dawn simulation, lights in your bedroom are programmed to come on gradually a few hours before you wake up in the morning.

Your doctor may also prescribe antidepressant medications, such as fluoxetine (for example, Prozac). Fluoxetine is a selective serotonin reuptake inhibitor (SSRI) that can improve the balance of certain brain chemicals that regulate mood.

Who is affected by SAD?
You are more likely to develop seasonal affective disorder if you are a female between the ages of 15 and 55. Between 60% and 90% of people with SAD are women, and those who have a relative with SAD are more likely to develop it. Older teens and young adults are also at risk for SAD. People living farther away from the equator develop SAD more often, but you can develop it no matter where you live.3 The risk of developing SAD for the first time decreases as you age.