Sleep Disorders

Seasonal Affective Disorder

Signs and Symptoms
Diagnosis
Treatment

Signs and Symptoms

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.

Common symptoms of SAD include:

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

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.

Reviewed by health care specialists at UCSF Medical Center.
Last updated November 4, 2007