Seasonal Affective Disorder
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Seasonal Affective Disorder


En Español (Spanish Version)


Seasonal affective disorder (SAD) is a type of depression that corresponds to seasonal changes in light. It most commonly occurs in late fall and lasts through the winter and into spring. It's not uncommon to feel "down" during the winter months. But people with SAD are not able to function normally during these months.

Brain—Psychological Organ

Brain face skull

SAD may be caused by fluctuations in hormones and brain chemicals.

© 2008 Nucleus Medical Art, Inc.


The cause of SAD is not completely understood. It is clearly related to changes in seasonal light.

Light affects cycles in the body. Lack of light during the winter months could possibly throw off levels of hormones and brain chemicals. This could contribute to the symptoms of SAD.

SAD often begins during adolescence or young adulthood.

Risk Factors

A risk factor is something that increases your chance of getting a disease or condition.

  • Sex: female
  • Living in northern latitudes


People with SAD have seasonal symptoms that come and go each year. They usually peak during the winter and disappear during the spring and summer.

Symptoms can include:

  • Depressed mood, feelings of sadness
  • Cravings for sweet or starchy foods
  • Overeating
  • Significant weight gain or loss
  • Lack of energy
  • Oversleeping or insomnia
  • Fatigue
  • Irritability
  • Social withdrawal
  • Difficulty concentrating
  • Decreased sexual desire


The doctor will ask about your symptoms and medical history, and perform a physical exam. You may be referred to a specialist in treating depression.

A diagnosis of SAD will only be made if you have some of the symptoms above and:

  • Your symptoms have occurred annually for at least two years
  • You have complete relief from symptoms during the summer months


Light Therapy

Light therapy is simple. The light box is made up of fluorescent bulbs, a reflective surface, and a diffusing screen. Ordinary household lighting is not sufficient. You sit a few feet away from the ultra-bright light for a certain amount of time each day, usually in the morning. You will be able to read or work during the therapy, as your eyes will remain open. Your doctor will probably start you off with 15 to 20 minutes a day. You will gradually increase the time, usually to 30 to 45 minutes daily.

There is some evidence that light therapy may be as effective as antidepressant therapy, but with fewer side effects. Participants in a recent study showed improvement within a week when they were exposed to a light box with 10,000-lux light treatment, which is equivalent to natural daylight on a bright spring morning. *

Tanning beds are not recommended as a source of light therapy. They give off ultraviolet light, which can increase the risk of cancer. They also have not been proven effective for treating SAD. Many people find that getting outdoors for a walk each day is also helpful.

Antidepressant Medications

Your doctor may prescribe antidepressant medications. These medications are usually prescribed when a person does not feel better with light therapy or if the depression is very severe.


Therapists can help you learn ways of managing stress and the symptoms of SAD.


There are no guidelines for preventing SAD because the cause is not understood. Researchers are studying the role of light therapy in preventing SAD. Light therapy just before the winter months and before the onset of depressive symptoms may prevent SAD from developing.


Depression and Bipolar Support Alliance (DBSA)

National Mental Health Association


Canadian Mental Health Center

Canadian Psychological Association


American Academy of Family Physicians website. Available at: .

National Mental Health Association website. Available at: .

Society for Light Treatment and Biological Rhythms website. Available at: .

*Updated section on Light Therapy on 7/20/06 according to the following study, as cited by DynaMed's Systematic Literature Surveillance : Lam RW, Levitt AJ, Levitan RD, et al. The Can-SAD study: a randomized controlled trial of the effectiveness of light therapy and fluoxetine in patients with winter seasonal affective disorder. Am J Psychiatry . 2006;163:805-812.

Last reviewed December 2007 by Theodor B. Rais, MD

Please be aware that this information is provided to supplement the care provided by your physician. It is neither intended nor implied to be a substitute for professional medical advice. CALL YOUR HEALTHCARE PROVIDER IMMEDIATELY IF YOU THINK YOU MAY HAVE A MEDICAL EMERGENCY. Always seek the advice of your physician or other qualified health provider prior to starting any new treatment or with any questions you may have regarding a medical condition.

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