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".
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