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Seasonal Affective Disorder

Weather often affects people's moods. Sunlight breaking through clouds can lift our spirits, while a dull, rainy day may make us feel a little gloomy. While noticeable, these shifts in mood generally do not affect our ability to cope with daily life. Some people, however, are vulnerable to a type of depression that follows a seasonal pattern. For them, the shortening days of late autumn are the beginning of a type of clinical depression that can last until spring. This condition is called "Seasonal Affective Disorder," or SAD.

A mild form of SAD, often referred to as the "winter blues," causes discomfort, but is not incapacitating. However, the term winter blues can be misleading; some people have a rarer form of SAD which is summer depression. This condition usually begins in late spring or early summer.

Awareness of this mental condition has existed for more than 150 years, but it was only recognized as a disorder in the early 1980s. Many people with SAD may not be aware that it exists or that help is available.

SAD can be a debilitating condition, preventing sufferers from functioning normally. It may affect their personal and professional lives, and seriously limit their potential. It is important to learn about the symptoms, and to know that there is treatment to help people with SAD live a productive life year-round.

What Causes SAD?

Research into the causes of SAD is ongoing. As yet, there is no confirmed cause. However, SAD is thought to be related to seasonal variations in light A biological internal clock in the brain regulates our circadian (daily) rhythms. This biological clock responds to changes in season, partly because of the differences in the length of the day. For many thousands of years, the cycle of human life revolved around the daily cycle of light and dark. We were alert when the sun shone; we slept when our world was in darkness. The relatively recent introduction of electricity has relieved us of the need to be active mostly in the daylight hours. But our biological clocks may still be telling our bodies to sleep as the days shorten. This puts us out of step with our daily schedules, which no longer change according to the seasons. Other research shows that neurotransmitters, chemical messengers in the brain that help regulate sleep, mood, and appetite, may be disturbed in SAD.

What are the Symptoms?

SAD can be difficult to diagnose, since many of the symptoms are similar to those of other types of depression or bipolar disorder. Even physical conditions, such as thyroid problems, can look like depression. Generally, symptoms that recur for at least 2 consecutive winters, without any other explanation for the changes in mood and behaviour, indicate the presence of SAD. They may include:

  • change in appetite, in particular a craving for sweet or starchy foods
  • weight gain
  • decreased energy
  • fatigue
  • tendency to oversleep
  • difficulty concentrating
  • irritability
  • avoidance of social situations
  • feelings of anxiety and despair

The symptoms of SAD generally disappear when spring arrives. For some people, this happens suddenly with a short time of heightened activity. For others, the effects of SAD gradually dissipate.

Symptoms of summer depression may include:

  • poor appetite
  • weight loss
  • trouble sleeping

Who is at Risk?

Research suggests that between 2% and 3% of the general population may have SAD. Another 15% have a less severe experience described as the "winter blues."

SAD may affect some children and teenagers, but it tends to begin in people over the age of 20. The risk of SAD decreases with age. The condition is more common in women than in men.

Recent studies suggest that SAD is more common in northern countries, where the winter day is shorter. Deprivation from natural sources of light is also of particular concern for shift workers and urban dwellers who may experience reduced levels of exposure to daylight in their work environments.

People with SAD find that spending time in a southerly location brings them relief from their symptoms. 

How is SAD Treated?

If you feel depressed for long periods during autumn and winter, if your sleep and appetite patterns change dramatically and you find yourself thinking about suicide, you should seek professional help, for example, from your family doctor. There is effective treatment for SAD. Even people with severe symptoms can get rapid relief once they begin treatment.

People with mild symptoms can benefit from spending more time outdoors during the day and by arranging their environments so that they receive maximum sunlight. Trim tree branches that block light, for example, and keep curtains open during the day. Move furniture so that you sit near a window. Installing skylights and adding lamps can also help.

Exercise relieves stress, builds energy and increases your mental and physical well-being. Build physical activity into your lifestyle before SAD symptoms take hold. If you exercise indoors, position yourself near a window. Make a habit of taking a daily noon-hour walk. The activity and increased exposure to natural light can raise your spirits.

A winter vacation in a sunny destination can also temporarily relieve SAD symptoms, although symptoms usually recur after return home. At home, work at resisting the carbohydrate and sleep cravings that come with SAD.

Many people with SAD respond well to exposure to bright, artificial light. "Light therapy," involves sitting beside a special fluorescent light box for several minutes a day. A health care professional should be consulted before beginning light therapy.

For people who are more severely affected by SAD, antidepressant medications are safe and effective in relieving symptoms. Counseling and therapy, especially short-term treatments such as cognitive-behavioral therapy, may also be helpful for winter depression.

Increasing your exposure to light, monitoring your diet, sleep patterns and exercise levels are important first steps. For those who are severely affected, devising a treatment plan with a health care professional consisting of  light therapy, medication and cognitive-behavioral therapy may also be needed.  

What treatments are available for SAD?

Research has shown that many patients with SAD improve with exposure to bright, artificial light, called light therapy, or phototherapy. As little as 30 minutes per day of sitting under a special fluorescent light box results in significant improvement in 60% to 70% of SAD patients.

Light Therapy

How does light therapy work?

We don't know, exactly, but research shows that light has a biological effect on brain chemical (neurotransmitters) and function. One theory is that people with SAD have a disturbance in the biological clock in the brain that regulates hormones, sleep and mood, so that this clock runs slow in the winter. The bright light may help to reset the clock and restore normal function. Other theories are that neurotransmitter functions, particularly serotonin and dopamine, are disturbed in SAD, and that these neurotransmitter imbalances are corrected by light therapy and/or antidepressant medications. Still other scientists believe that patients with SAD have reduced retinal light sensitivity in the winter that is corrected by light therapy. There is also evidence for a genetic basis for SAD.

How do you use light therapy?

A fluorescent light box is the best-studied light therapy treatment. Patients usually purchase a lightbox and use it in their own homes. The usual "dose" of light is 10,000 lux, where lux is a measurement of light intensity. Indoor light is usually less than 400 lux; a cloudy day about 3,000 lux; and a sunny day is 50,000 lux or more. Using the light box for about 30 minutes a day is usually enough for a beneficial response.

How do I get a lightbox?

Safe and portable lightboxes are now commercially available. Ask your doctor, or contact our clinic for more information. The cost of a lightbox is usually between $200 and $400. We do not recommend building your own lightbox, because of the safety hazards, and the difficulty in getting the correct dose of light.

Are there side effects to light therapy?

Side effects of light therapy are usually mild. Some people may experience nausea, headaches, eye strain, or feeling edgy when they first start using the lightbox. These effects usually get better with time.

There are no known long-term harmful effects of light therapy. However, people with certain medical conditions (such as retinal disease or diabetes) or taking certain medications should have special eye examinations before considering light therapy.

Other Treatments

Are there other treatments for SAD?

Other treatments for depression, including the newer antidepressant medications (e.g., selective serotonin reuptake inhibitors, or SSRIs) are also effective for patients with SAD. Counselling may also help. People with milder symptoms of the winter blahs may be helped by simply spending more time outdoors and exercising regularly in the winter (e.g., a daily noon hour walk).

Where To Go For More Information

For further information about seasonal affective disorder, contact a community organization to find out about support and resources in your community.

Thanks to:
Canadian Mental Health Association
UBC site on Seasonal Affective Disorder.


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last updated July, 2014