Seasonal Affective Disorder (SAD)

Seasonal affective disorder (SAD) is a form of depression that occurs at the same time each year (usually with the onset of winter) and disappears at the same time each year (typically at the start of spring). SAD is linked to the availability of daylight and occurs most often in people who live in the Northern Hemisphere.

What Is SAD?

Many people get the winter blahs or cabin fever as the days get shorter and colder, but for the approximately 10 million Americans with SAD, shorter days mean a slide into true depression. SAD is a seasonal pattern of depression. Women experience this form of depression four times more often than men, and it can also occur in children and teens. The farther individuals live from the equator, the higher the risk that they will experience SAD. Some studies suggest there may be genetic factors that influence which people are more susceptible. SAD rates are typically higher in younger people and decrease with age.

One study has estimated the incidence of SAD in the general population as only 1.4 percent in Florida but 9.7 percent in New Hampshire. These numbers suggest that the condition strikes people who live in the northern United States about seven times more frequently than it does people who live in the South. The study also showed that SAD affected more people in other Northern states: 4.7 percent in New York and 6.3 percent in Maryland. SAD rates vary around the world in similar patterns. For example, in Turkey the rate is 4.8 percent, compared with Scotland at 9.9 percent and Siberia at 16.2 percent.

What Causes Seasonal Affective Disorder?

As autumn arrives, the number of daylight hours declines. The effect is greater the farther north a person travels from the equator. Daylight also declines with increasing cloud cover in specific areas of the United States, such as the Great Lakes region and the northwestern coastal areas of Washington.

Researchers believe that for some people, the decrease in available daylight causes a decline in the neurotransmitter * serotonin in the brain. A decrease in serotonin in the brain has been linked to depression because serotonin typically is associated with feelings of well-being. In the autumn, after a few weeks of reduced serotonin levels, a person can start to show signs of depression. If left untreated, the depression may continue throughout the winter and then disappear in the spring as the number of daylight hours increases.

Medical professionals diagnose SAD in people if they become depressed in the fall and winter for two or more consecutive years with periods of normal moods in the spring and summer, and if they have no other problems that might account for seasonal depression. A rare form of SAD, called summer SAD, occurs in reverse of the normal pattern. People with summer SAD become depressed during the summer and feel better in the winter.

What Are the Symptoms of Seasonal Affective Disorder?

Not everyone who has SAD experiences all of the same symptoms. Common symptoms of SAD include fatigue and oversleeping, a craving for carbohydrates (such as breads and pasta), and a tendency to gain a little weight. In addition, a person may experience other common symptoms of depression including:

A patient uses light therapy to treat seasonal affective disorder (SAD).

A patient uses light therapy to treat seasonal affective disorder (SAD).
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How Do Doctors Treat Seasonal Affective Disorder?

Following a correct diagnosis, a medical professional may recommend that the patient begin light therapy to treat seasonal affective disorder. The individual sits in front of special bright light boxes or wears light visors for a period of 30 minutes to two hours every day, glancing occasionally at the light. To be effective, the light must enter the eyes and not just fall on the skin. Occasionally, people report eyestrain or headaches from the light devices, but they usually experience no other negative side effects. When natural daylight increases, people with SAD discontinue light treatment.

In addition to light therapy, some people with SAD benefit from antidepressant medications * . Some researchers have also advocated the use of melatonin, a light-sensitive hormone * that is believed to play a role in the normal sleep-wake cycle. They believe that SAD results when the body's normal cycle becomes skewed, and the timed administration of melatonin can help restore the normal pattern.

See also Depressive Disorders: Overview • Psychopharmacology


Books and Articles

Contie, Vicki, Meghan Mott, and Harrison Wein. “Beat the Winter Blues: Shedding Light on Seasonal Sadness.” NIH News in Health, January 2013. (accessed July 6, 2016).

Khazan, Olga. “When Summer Is Depressing.” The Atlantic, July 31, 2014. (accessed July 6, 2016).


MedlinePlus “Seasonal Affective Disorder.” U.S. National Library of Medicine. (accessed July 6, 2016).

NHS Choices. “Beating the Winter Blues.” (accessed July 6, 2016).

PubMed Health. “Depression.” U.S. National Library of Medicine. (accessed July 6, 2016).


Mental Health America. 2000 N. Beauregard St., 6th Floor, Alexandria, VA 22311. Toll-free: 800-969-6642. Website: (accessed July 6, 2016).

Seasonal Affective Disorder Association. PO Box 332, Wallingford, England OX10 1EP. Website: (accessed July 6, 2016).

* neurotransmitter (NUR-o-tranzmit-er) is a brain chemical that lets brain cells communicate with each other. Therefore, it allows the brain to function properly. In other words, a neurotransmitter transmits (carries) a chemical message from neuron to neuron.

* antidepressant medications are used for the treatment and prevention of depression.

* hormone is a chemical substance that is produced by a gland and sent into the bloodstream carrying messages that affect other parts of the body.

  This information is not a tool for self-diagnosis or a substitute for professional care.