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Seasonal Affective Disorder


Seasonal affective disorder (SAD) is a form of depression that occurs during specific seasons, most commonly during the fall and winter. However, the condition can occur at any time of the year, including during the summer. The cause of SAD is not yet known, but it's believed to be related to the availability of sunlight. Light affects your internal body clock, which helps you regulate when to sleep and when to be awake.

Some scientists believe that a fluctuation in the body's production of melatonin, a hormone that helps induce sleep, might be the cause of SAD. Other researchers speculate that a lack of serotonin, a brain chemical or neurotransmitter that seems to be triggered by sunlight, is the cause of SAD. People who are depressed often have decreased levels of serotonin in their brains.

The incidence of the condition varies with geography. For example, it tends to be more common in the northern or polar regions. One study found a 10 percent occurrence in New Hampshire and only a 2 percent rate in Florida.

Our Approach to Seasonal Affective Disorder

UCSF offers thorough assessments and personalized care for mood disorders, including seasonal affective disorder. Treatment options include light therapy, medications and psychotherapy to help patients identify and avoid triggers. We also offer guidance on simple lifestyle adjustments that may help, such as taking a regular morning walk.

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Signs & symptoms

Common symptoms of seasonal affective disorder (SAD) include:

  • Increased appetite
  • Weight gain
  • Inactivity and low energy levels
  • Excessive sleep
  • Negative feelings and depression
  • Headaches
  • Anxiety
  • Self-imposed isolation


Seasonal affective disorder (SAD) can be difficult to diagnose because it's hard to differentiate from other forms of depression. Your doctor will ask about your symptoms and how long you have been experiencing them — in particular, whether you've experienced symptoms of SAD for at least two consecutive years and whether it was during the same season each year.

In addition, your doctor will want to know if the periods of depression were followed by seasons when you did not feel depressed. Lastly, your doctor will want to make sure that there are not other explanations for the changes in your mood or behavior.


If you are diagnosed with seasonal affective disorder (SAD), your doctor may choose one of several approaches to your treatment.

  • Light Therapy Short periods of exposure to light can help ease depression. Doses of sunlight are measured in "lux." For example, the sun emits about 90,000 lux and blue sky reflects about 45,000 lux. Treatments could range from two hours of light at 2500 lux every morning to 30 to 40 minutes of light at 10,000 lux every morning. However, light therapy in the evening may interrupt sleep patterns. There are few, if any, side effects to the eyes from using light therapy. Sometimes, an hour walk in the morning can help without any other treatment.
  • Medication Your doctor may prescribe an antidepressant in combination with light therapy or if light therapy isn't effective. Antidepressants often are used when the condition occurs in the summer.
  • Psychotherapy Psychotherapy may help you identify ways to avoid behaviors or environments that tend to trigger episodes of SAD, or to reduce stress in your life, which may worsen the symptoms.

In addition to the treatments described above, there are a number of things you can do to help your body cope with seasonal depression. For example, try increasing the amount of light in your home or workplace by opening window shades. Increase your physical activity as exercising regularly can help relieve stress. Also, you may want to consider visiting a warm, sunny place during the winter, such as vacationing in a tropical location.

UCSF Health medical specialists have reviewed this information. It is for educational purposes only and is not intended to replace the advice of your doctor or other health care provider. We encourage you to discuss any questions or concerns you may have with your provider.

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