Seasonal affective disorder (SAD) is a type of
depression. It is associated with the seasonal changes in light. SAD most commonly occurs in late fall and lasts through the winter and into spring. SAD is more than feeling down, it interferes with normal daily functions during these times.
SAD may be caused by fluctuations in hormones and brain chemicals.
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The causes of SAD are not completely clear. Some factors that may play a role include:
- Reduced sunlight—This affects internal clocks, readjusting hormones and brain chemicals.
- Increase in melatonin production—Melatonin may cause symptoms of depression. This hormone is produced in higher amounts in the dark.
- Low serotonin—Serotonin is a brain chemical that is associated with well-being. In people with SAD, there may be a lack of serotonin in the brain.
SAD is more common in women than in men, often appearing in young adulthood. People who live in northern latitudes also have an increased risk of developing SAD.
Symptoms appear and peak during the winter months. As spring and summer approach, symptoms disappear. SAD may cause:
- Depressed mood, feelings of sadness
- Fatigue/lack of energy
- Social withdrawal
- Difficulty concentrating
- Decreased sexual desire
- Weight gain
- Cravings for sweet or starchy foods
The doctor will ask about your symptoms and medical history. A physical and psychological exam will be done.
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 2 years
- No nonseasonal major depressive episodes have occurred during same period
- You have complete relief from symptoms during the summer months
Light therapy provides a special type of lighting to your body. Therapy includes sitting a few feet away from an 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. Treatment usually lasts about 30 minutes each day.
There is some evidence that light therapy may be as effective as
antidepressant therapy, but with fewer side effects.
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.
Your doctor may prescribe antidepressant medications or supplements.
Therapists can help you learn ways of managing stress and the symptoms of SAD.
If you have SAD each year, your doctor may make suggestions to help prevent the symptoms from coming. For example, certain antidepressants or light therapy may be used to prevent SAD symptoms from coming if started before autumn.
Johansson C, Smedh C, et al. Seasonal affective disorder and serotonin-related polymorphisms.
Neurobiology of Disease.
Seasonal affective disorder. American Academy of Family Physicians website. Available at:
http://familydoctor.org/familydoctor/en/diseases-conditions/seasonal-affective-disorder.html. Updated September 2012. Accessed September 28, 2014.
Seasonal affective disorder. EBSCO DynaMed website. Available at:
http://www.ebscohost.com/dynamed. Updated December 19, 2012. Accessed September 28, 2014.
7/20/06 DynaMed's Systematic Literature Surveillance.
http://www.epnet.com/dynamed/what.php: Lam RW, Levitt AJ, 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 August 2014 by Michael Woods, 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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