Seasonal Affective Disorder

Seasonal Affective Disorder, or SAD, is a depression that normally occurs in winter months, in response to changes in the natural day/night cycle. Artificial light therapy is an effective treatment.


Seasonal affective disorder (also called SAD) is a type of depression that follows the seasons. The most common type of SAD is called winter depression. It usually begins in late fall or early winter and normal mood returns in summer. A less common type of SAD, known as summer depression, usually begins in the late spring or early summer. SAD may be related to changes in the amount of daylight you get.

Seasonal affective disorder is estimated to affect 10 million Americans. Another 10 percent to 20 percent may have mild SAD. SAD is more common in women than in men. Illness typically begins around age 20. Some people experience symptoms severe enough to affect quality of life, and 6 percent require hospitalization. Many people with SAD report at least one close relative with a psychiatric disorder, most frequently a severe depressive disorder (55 percent) or alcohol abuse (34 percent). Although some children and teenagers get SAD, it usually doesn't start in people younger than age 20. Yet when it does the syndrome is first suspected by parents and teachers. Risk decreases with age. SAD is more common the farther north you live.


Not everyone with SAD has the same symptoms, but common symptoms of winter depression include the following:

  • Feelings of hopelessness and sadness
  • Thoughts of suicide
  • Hypersomnia or a tendency to oversleep
  • A change in appetite, especially a craving for sweet or starchy foods
  • Weight gain
  • A heavy feeling in the arms or legs
  • A drop in energy level
  • Decreased physical activity
  • Fatigue
  • Difficulty concentrating
  • Irritability
  • Increased sensitivity to social rejection
  • Avoidance of social situations

Symptoms of the summer SAD are:

  • Poor appetite
  • Weight loss
  • Insomnia
  • Agitation and anxiety

Either type of SAD may also include some of the symptoms that are present in other kinds of depression, such as feelings of guilt, a loss of interest or pleasure in activities previously enjoyed, ongoing feelings of hopelessness or helplessness, or physical problems such as headaches and stomachaches.

Symptoms of SAD tend to reoccur at about the same time every year. The changes in mood are not necessarily related to obvious seasonal stressors (like being regularly unemployed during the winter). Usually depression is mild or moderate. However, some people experience severe symptoms and 6 percent of SAD patients need hospitalization at some time in their lives.

Seasonal Affective Disorder can be misdiagnosed as hypothyroidyism, hypoglycemia, or a viral infection such as mononucleosis.


The cause for SAD is unknown. One theory is that it is related to the amount of melatonin in the body, a hormone secreted by the pineal gland. The body is exposed to its secretions for a shorter period of time during summer because light suppresses it production. The long nights of winter extends the amount of time melatonin is released into the body, thus increasing symptoms. It is not clear how melatonin produces the symptoms reported. One possible explanation is that melatonin causes a drop in body temperature and lower body temperature is associated with sleep. This could indicate that it is related to the sleep-wake cycle and related to the hypersomnia and fatigue reported.


Because winter depression is probably caused by a reaction to a lack of sunlight, broad-band light therapy is frequently used. This therapy requires a light box or a light visor worn on the head like a cap. The individual either sits in front of the light box or wears light visor for a certain length of time each day. Generally, light therapy takes between 30 and 60 minutes each day throughout the fall and winter. The amount of time required varies with each individual. When light therapy is sufficient to reduce symptoms and to increase energy level, the individual continues to use it until enough daylight is available, typically in the springtime. Stopping light therapy too soon can result in a return of symptoms.

When used properly, light therapy seems to have very few side effects. Side effects include eyestrain, headache, fatigue, irritability and inability to sleep (when light therapy is used too late in the day). People with manic depressive disorders, skin that is sensitive to light, or medical conditions that make their eyes vulnerable to light damage may not be good candidates for light therapy.

When light therapy does not improve symptoms within a few days, then medication and, or, behavioral therapies should be introduced. In some cases, light therapy can be used in combination with anyone or all of these therapies.


  • Monitor your mood and energy level
  • Take advantage of available sunlight
  • Plan pleasurable activities for the winter season
  • Plan physical activities
  • Approach the winter season with a positive attitude
  • When symptoms develop seek help sooner rather than later


  • American Psychiatric Association
  • Diagnostic and Statistical Manual of Mental Disorders, 4th Edition
  • What is seasonal affective disorder?
  • National Alliance of Mental Illness
  • National Institute of Mental Health
  • U.S. Department of Health and Human Services; 2005
  • National Mental Health Association
  • American Family Physician
  • Substance Abuse and Mental Health Services Administration
Last reviewed 11/18/2015