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Seasonal affective disorder | page 1, 2
Light therapy comes in all sizes, colors and intensities. Although
Rosenthal's original experiments used full-spectrum fluorescent tubes, his later research showed that light from incandescent and
halogen bulbs was just as effective. No one bulb is definitely better than another. Even intensity may not matter. Amount of exposure time is also unclear. Despite a lack of evidence for superiority
of any specific light source, the standard seems to be full-spectrum non-ultraviolet fluorescent tubes because of their even disbursement of light and cool operating temperatures. A typical treatment strategy begins with having the patient set up a light box on a table to sit directly in front of while eating breakfast or reading the newspaper. Exercise is also a critical element of treatment. Dr. Rosenthal suggests taking a quick walk during lunch breaks. Even on overcast days, the sunlight filtering through the clouds is beneficial. In the evenings the patient can have another session in front of the light box, perhaps while eating dinner. (Estimates as to optimal exposure vary; some say that 60 to 80 percent of patients feel better with as little as 30 minutes under the lamp.) It's not necessary, or even recommended, to stare into the light.
The entire retina responds to light, so it's possible to get the full
benefit of light therapy while reading, talking on the phone or even watching television. I have friends who swear by the light treatment. I personally feel better on sunny days. But how specific is SAD? Is it a discrete disorder, or merely an extension of ordinary depression? I hear "Jingle Bells" or "Rudolph the Red-Nosed Reindeer" and I look around for a sharp knife, a nice comforting loop of rope, a plastic bag inscribed "Here lies a man who detested the holiday season." I doubt that standing in front of a searchlight would make a difference. Even the constitutionally euphoric get depressed when double-parked in standstill traffic while the spouse runs in
to a jam-packed mall to exchange that scratchy purple sweater from your aunt in Toledo. Fifteen years have passed since Rosenthal's original paper, but I'm still a bit in the dark about SAD. If the disorder is related to diminution in light exposure, shouldn't the prevalence of SAD be greater at higher latitudes? Some studies say yes, others show no difference. And some Northerners (Icelanders in particular) appear peculiarly immune to the disorder. Does this negate the light hypothesis or merely point to other complicating factors such as genetically influenced decreased susceptibility to depression? That was Rosenthal's speculation -- but no one knows for sure. The issues of duration and intensity of light exposure remain unanswered. Rosenthal now believes that light intensity may not be an issue -- in fact levels as low as those mimicking the beginning of dawn can be therapeutically effective. And there is the problem of assessing light therapy against a placebo. I cannot imagine what would be used as a non-light source placebo. So we are left with a common-sense observation that lack of light seems to cause depression in winter. Science has provided some tantalizing clues but no final answer; there's more to darkness than meets the eye. In the meantime, keep warm, exercise (preferably outdoors), eat sensibly and, above all, keep well lit.
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