Seasonal affective disorder: How effective is light therapy?

Blue Monday — the third Monday in January — has been called the most depressing day of the year.

While there's no scientific proof of Blue Monday's effect, for many British Columbians, the winter blahs are in full swing with shorter daylight hours and sinking temperatures dragging moods down with them.

Light therapy has been pointed to as solution to seasonal affective disorder, but can 30 minutes in front of a high intensity, UV-filtered light really brighten your day that much?

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According to Dr. Anthony Levitt, a psychiatrist and the chief of Toronto's Sunnybrook Hospital Brain Sciences Program, before talking about treatment, the first step is to distinguish between a general downturn in mood and diagnosable SAD. 

"We are seasonal beings. It is statistically normal to have difficulty in some respect with it, whether it's a mood or energy in the wintertime," he said.

"What we're talking about is the two or three per cent of people who have persistent and consistent low mood, loss of energy, virtually every day and virtually all day for days and weeks at a time, so much so that it influences their vocation, their interpersonal relationships," he said.

For the majority of those who've tried it, light therapy can offer reliable relief. Levitt says the treatment is effective in about 60 per cent of patients.

"It works pretty quickly. It has side effects, but relatively few side effects, and they're not that intense. So it's an excellent treatment."

According to the Mayo Clinic, the side effects of light therapy include eyestrain, headache, nausea and irritability, but they are often short-lived.

The difficulty is that in the medical community, there is still much to learn about SAD.

Questions left to answer

Doctors still don't know for certain why some people suffer from SAD and others don't.

Levitt points to a possible enhanced sensitivity to light. Some studies have also suggested genetics could come into play.

There is also no concrete answer as to why light therapy itself is an effective antidote. 

"It's a very good question, we don't know. We do know that light hits the retina, and the retina is actually part of the brain. And when light hits the retina at a particular time of day when it's most sensitive to light, there's a cascade of changes that normalize or return the brain to pre-depressed function," said Levitt.

He sees finding answers to those remaining questions as a positive, even outside the realm of SAD itself. 

"Seasonal depression is a unique condition. There are very few mental illnesses where we know about when it's going to start and about when it's going to get better," he said, "If we understand what goes on in seasonal depression, we should be able to interpret that and extrapolate to what goes on in [non-seasonal] depression."