Multiple: Seasonal Affective Disorder

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Multiple: Seasonal Affective Disorder

Causes and Symptoms
The Future
For more information


Seasonal affective disorder, or SAD, is a form of depression related to the changes in the seasons. Most people with SAD feel tired, depressed, and uninterested in life during the fall and winter and feel happier and more energetic in spring and summer. There are, however, some people who follow the opposite pattern, feeling depressed in spring and summer and livelier in fall and winter. This summer pattern is sometimes called summer SAD, reverse seasonal affective disorder, or RSAD.


Seasonal affective disorder has troubled humans, particularly those living at some distance from the equator, for centuries. It used to be part of common folk wisdom that the changing seasons affect the way people feel. With the coming of electric lighting and indoor climate control, however, modern people are less in touch with the influence of seasonal changes in temperature and light intensity on human moods. Dr. Thomas Wehr, an expert on SAD, commented in an interview in 2002 that “We've kind of de-seasonalized ourselves as much as possible. You know, we turn the lights on after dark, we turn the heat on in winter, we turn the air conditioning on in summer, and you could almost not notice [the weather].”

The symptoms of winter SAD vary in intensity in the general North American population. Some people are only mildly affected, feeling some loss of energy during the winter, a tendency to oversleep and gain weight, an increased craving for starchy foods, and lowered interest in social activities, but others feel severely depressed to the point of requiring hospitalization. The symptoms of RSAD are somewhat different, with people feeling agitated or jumpy, finding themselves having difficulty sleeping, and in some cases, thinking about suicide.


Researchers at the National Institute of Mental Health (NIMH) estimate that as many as 5 percent, or 15 million Americans suffer severely from SAD, with another 33 million feeling some moodiness or loss of creativity or productivity during the winter. There appears to be some connection between geographical location and the risk of SAD, with the rates of winter SAD increasing from south to north in the United States. About 1.5 percent of people in Florida have winter SAD, compared to 9 percent in Minnesota and Maine. Areas with overcast skies in the winter also have higher rates of SAD than those with relatively clear winter weather.

Women are about twice as likely as men to suffer from SAD. The disorder is most likely to appear in the early adult years, but some patients report symptoms of SAD going back to childhood.

About 85 percent of patients with SAD have the winter blues, with the remaining 15 percent having summer SAD. Summer SAD is more common in hotter climates, such as India, parts of China, or the American South.

A Doctor's SAD Story

Dr. Norman Rosenthal, the psychiatrist who first identified seasonal affective disorder (SAD), grew up in South Africa, where the length of daylight at different times of the year does not vary as much as it does in most parts of the United States. In the summer of 1976 Rosenthal moved to New York City and was surprised by the difference between the energy he enjoyed during the warm months and a tiredness that began almost as soon as daylight saving time ended. He moved in 1977 to the National Institute of Mental Health (NIMH) in Maryland and met several patients who seemed to suffer from depression related to the seasons.

Rosenthal and several colleagues experimented with having these patients sit in front of boxes containing light bulbs covered by a plastic screen for several hours a day and were surprised by how quickly the patients responded to light therapy. At first the doctors thought this seasonal type of depression might be very rare. They decided to contact the health journalist at the Washington Post to see whether there might be other people in the Washington area with the condition. They received thousands of phone calls from people all over the United States who were eager to participate in research that might help them. By 1981 Rosenthal recognized that his first winter in the United States was an indication of his own mild form of SAD.

Causes and Symptoms

The causes of SAD are not completely understood, but there are several theories that have been proposed to explain the disorder:

  • Genetic factors. About two-thirds of people diagnosed with SAD have at least one relative with depression or another mood disorder.
  • Abnormal levels of melatonin. Melatonin is a hormone produced by the pineal gland in the brain that regulates the daily circadian rhythm (sleep/wake cycle) in humans. Humans generally produce more melatonin during the long nights of winter, and some researchers think that overproduction of melatonin in some people may be responsible for the depressed mood of SAD.
  • Disruption of the circadian rhythm caused by the decreasing levels of sunlight in fall and winter. There are some researchers who think that SAD is related to jet lag, another form of depression that is associated with disruption of a person's usual sleep/wake pattern caused by traveling across too many time zones too rapidly.
  • Lack of serotonin. Serotonin is a neuro-transmitter (chemical produced by the brain) that is known to affect mood. The lower levels of sunlight in the winter are thought to cause a drop in serotonin production, which in turn leads to depression.

The causes of summer SAD are less clear-cut. Some doctors think that it may be more related to summer heat than to seasonal changes in light levels.

The symptoms of winter SAD typically include:

  • Oversleeping, having difficulty getting up in the morning.
  • Craving for heavy, starchy foods and sweets. Some people with winter SAD gain so much weight every winter and lose it in the summer that they have wardrobes in two different sizes for the different seasons.
  • Lack of interest in work or social activities.
  • Feelings of depression and hopelessness.
  • Difficulty concentrating or paying attention.

The symptoms of summer SAD include:

  • Anxiety
  • Loss of appetite and weight loss
  • Insomnia
  • Agitation
  • Irritable mood


The diagnosis of SAD is based on the doctor's discussion of the patient's symptoms with him or her and completion of a set of questionnaires about SAD. The patient will usually be asked about seasonal changes in mood and behavior, his or her lifestyle and social situation, and sleeping and eating patterns. In most cases the doctor will also give the patient a physical examination to rule out changes in mood that could be caused by thyroid disease or other disorders.


Treatment for winter SAD usually includes light box therapy, in which a person sits in front of a box containing bright white lights covered by a plastic filter to prevent glare. Treatments usually last for thirty to sixty minutes in the morning (or whatever time of day works best for the patient). The patient is instructed to sit near the box with eyes open but without staring at the box. People who find light boxes inconvenient are sometimes helped just by taking walks outside in the winter during

daylight hours. One advantage of light therapy is that it is easy to use and has few side effects.

Other treatments for winter SAD include antidepressant medications; timed doses of melatonin in the early evening to shift the body's circadian rhythm; and psychotherapy to help people cope with the mood changes of winter SAD.

Some people with summer SAD are helped simply by staying in air-conditioned environments as much of the time as they can, but others need antidepressant medications as well.


The prognosis of SAD depends on the severity of the patients' symptoms and whether they have another mental disorder in addition to SAD. People with only mild symptoms often do well on their own by using more bright lights in their homes in the winter and spending more time outside.

Between 50 and 80 percent of patients with severe SAD benefit from light box therapy, and about 67 percent of patients feel better when treated with antidepressants. Timed doses of melatonin appear to be less effective with most people.

Patients who suffer from major depression as well as SAD should be treated for both disorders. About 20 percent of patients with severe SAD are eventually diagnosed with bipolar disorder.


There is no known way to prevent SAD, but learning about the condition and beginning treatment each year before the seasonal symptoms get underway can keep them from getting worse as the season progresses. Sticking to a treatment plan and getting regular physical exercise are also ways to minimize the effects of SAD on one's life.

The Future

Researchers are hopeful that better understanding of the causes of both winter and summer SAD will lead to more effective treatments, as none of the present therapies work for all patients with the disorder.

SEE ALSO Bipolar disorder; Depression


Circadian rhythm: The medical name for the daily sleep/wake cycle in humans.

Jet lag: A sleep disorder or disturbance in the sleep/wake cycle related to rapid travel across time zones.

Melatonin: A hormone produced in the pineal gland in the brain that regulates the sleep/wake cycle.

Serotonin: A chemical produced in the brain that regulates mood.

For more information


Rosenthal, Norman E., M.D. Winter Blues: Everything You Need to Know to Beat Seasonal Affective Disorder. New York: Guilford Press, 2006.

Smith, Laura, and Charles Elliott. Seasonal Affective Disorder for Dummies. Indianapolis, IN: Wiley Publishing, Inc., 2007.


Brody, Jane E. “Getting a Grip on the Winter Blues.” New York Times, December 5, 2006. Available online at (accessed May 8, 2008).

Friedman, Richard A., M.D. “Brought On by Darkness, Disorder Needs Light.” New York Times, December 18, 2007. Available online at (accessed May 8, 2008).

Ivry, Sara. “Seasonal Depression Can Accompany Summer Sun.” New York Times, August 13, 2002. Available online at health&spon=&pagewanted=all (accessed May 9, 2008). This is an article about summer SAD.


Center for Environmental Therapeutics. Home Page. (accessed May 8, 2008). This a Web site with information about light therapy for SAD, advice about the use of light boxes for self-treatment, and an online questionnaire to help individuals determine the time of day that light therapy would be most beneficial for them.

Mayo Clinic. Seasonal Affective Disorder. Available online at (updated September 24, 2007; accessed May 9, 2008).

National Alliance on Mental Illness (NAMI). Seasonal Affective Disorder. Available online at (updated 2004; accessed May 9, 2008).

TeensHealth. Seasonal Affective Disorder. Available online at (updated January 2007; accessed May 9, 2008).

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Multiple: Seasonal Affective Disorder

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