UBC/VHHSC Mood Disorders Clinic - Many people feel mildly "depressed" during the winter, but some people have more severe bouts of feeling down all the time, low energy, problems with sleep and appetite, and reduced concentration to the point where they have difficulty functioning at work or in the home. We say that these people have a clinical depression, to distinguish it from everyday ups and downs. Seasonal affective disorder (affective is a psychiatric term for mood), or SAD, describes people who have these clinical depressions only during the autumn and winter seasons. During the spring and summer, they feel well and "normal".

The common symptoms of SAD include:

Extreme fatigue and lack of energy
Increased need for sleep; sleeping much more than usual
Carbohydrate craving and increased appetite
Weight gain

How common is SAD?

Researchers believe that SAD results from the shorter daylength in winter. Recent studies estimate that SAD is more common in northern countries because the winter day gets shorter as you go farther north. In Florida, less than 1% of the general population have SAD, while in Alaska as many as 10% of people may suffer from winter depression. In B.C., 2% to 5% of people probably have SAD. This means that up to 200,000 people in British Columbia may have difficulties in the winter due to significant clinical depression.

What treatments are available for SAD?

An exciting new research finding is 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 lightbox results in significant improvement in 60% to 80% of SAD patients. Side effects of light therapy are mild, although people with certain medical conditions or taking certain medications should avoid light therapy. Other treatments for depression, including antidepressant medications and counseling, may also be helpful for patients with SAD. People with milder symptoms of the "winter blahs" may be helped by simply spending more time outdoors and exercising regularly in the winter.

Why does light therapy work?

We don't know, exactly, but research shows that light has a biological effect on brain hormones 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 changes in brain chemical (neurotransmitter) function, particularly serotonin and dopa-mine, may be disturbed in SAD, and that these neurotransmitter imbalances are corrected by light therapy and/or anti-depressant medications. Still other scientists believe that patients with SAD have reduced retinal light sensitivity in the winter that is corrected by light therapy.