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What Is SAD?

Seasonal Affective Disorder Can Be Treated with Light Box


Updated February 10, 2014

Written or reviewed by a board-certified physician. See About.com's Medical Review Board.

What Is SAD?

A man uses a light box to treat his seasonal affective disorder.

Christopher Furlong / Getty Images

Seasonal affective disorder (SAD) is a subtype of depression that seems to follow a seasonal pattern. Aside from the timing, SAD shares many of the same features of typical depression.

In most cases, the symptoms of SAD come on as the days become shorter. This fall onset leads to the condition’s alternative name: winter depression. In this instance, the symptoms tend to remit with summer’s return. However, there is a less common alternative type of SAD that actually occurs with a spring-onset pattern.

Symptoms of SAD

The features of fall-onset SAD include what are called the atypical symptoms of depression, such as:

  • Increased desire to sleep
  • Increased appetite with carbohydrate cravings
  • Increased weight
  • Irritability
  • Interpersonal difficulty
  • Heavy feelings in the arms or legs

In contrast to this, the spring-onset SAD has so-called typical symptoms of depression, including weight loss, insomnia, and poor appetite.

How Common Is SAD?

SAD tends to occur in the more northern regions of the world and may affect up to 10 percent of people. It more commonly occurs in women. The average age of onset seems to be about 23 years, and as people get older the risk of having SAD actually decreases.

What Causes SAD?

The cause of SAD is not fully understood. Logically, people who are predisposed to developing the condition may be sensitive to changes in the amount of daylight. As the days become shorter, and the exposure to daylight decreases, there may be an adverse effect on their circadian rhythms. These rhythms help to control metabolism, sleep patterns, hormonal changes, and, conceivably, even mood.

One possible mitigating factor in all this is a chemical (or neurotransmitter) within the brain called serotonin. Serotonin levels have been shown to vary in healthy people with as seasons change. The ultimate role of this in SAD is still being worked out.

Treatment Options for SAD

There are many effective options for the treatment of SAD. As it is a subtype of depression, many of the therapies are very similar to those used in that condition, with the exception of light therapy as a useful alternative.

Light therapy involves the use of a light box that generates a standard wavelength and amount of light. Exposure to this light is thought to affect the circadian rhythm that may be disrupted as the days become shorter. Light therapy has very few side effects and is usually well tolerated.

In addition, standard treatments of depression, including medications, may be helpful. No studies have examined the use of electroconvulsive treatments or psychotherapy for SAD, but there may be situations where these options may likewise prove useful.

If you think you suffer from SAD, start by speaking with your doctor about your concerns and investigate whether treatment may help you to feel better throughout all the seasons of the year.


American Academy of Sleep Medicine. "International classification of sleep disorders: Diagnostic and coding manual." 2nd ed. 2005.

American Psychiatric Association. "Diagnostic and Statistical Manual of Mental Disorders. " 4th ed. American Psychiatric Association, Washington DC, 2000.

Eagles, JM. "Seasonal affective disorder. " Br J Psychiatry. 2003;182:174.

Partonen, T., et al. "Seasonal affective disorder." Lancet 1998;352:1369.

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