Since the dawn of time man has recognized not only the therapeutic effects of light, but its life-sustaining qualities. From plant photosynthesis to the sleep-wake cycle of animals, all living things are vitally affected by the presence, absence, and type of light exposure. Light and its personification even play a pivotal role in our festivals, beliefs, and legends.
In the absence of light, all life shrivels and dies. Some humans are even badly affected when daylight levels begin to decline in the late summer and autumn. We begin to gain weight, sleep excessively, experience an increase in irritation and anxiety, and a decline in libido, energy, and alertness. In more severe cases, some people become completely unable to function.
This is winter depression, the “winter blues,” or as it’s clinically known, Seasonal Affective Disorder (SAD). In upper latitudes, this condition affects 15 percent of the population; one-third of which suffer severely. Three times more women than men suffer from SAD. Historically, this disorder was indistinguishable from other depressions. Only within the last 25 years have researchers observed that its seasonality suggested some sort of pathology or physiological disorder. Alot of the work has and continues to be done at the National Institute of Mental Health at the NIH in Bethesda, MD, and at many other research labs and clinical facilities.
When researchers realized that this seasonal depression was more prevalent in northern latitudes, they surmised that it was indirectly caused by light deprivation. The discovery that bright light falling on the eyes will suppress the secretion of melatonin in humans led to the innovation of light treatment for SAD. Clinical studies to test this hypothesis yielded mixed results.
Today, there’s more debate than consensus on what causes SAD. The good news is that light therapy works; the bad news is no one is sure why. Although melatonin levels are commonly accepted as an effective indicator of the biological effects of light (i.e., suppression of melatonin), it is not at all clear what effect, if any, melatonin has on mood and behavior.
The most promising research relates to the study of serotonin. Serotonin is responsible for transmitting electrical signals from one nerve cell in the brain to the next. Many factors indicate abnormalities in brain serotonin may be at the basis of SAD. Serotonin concentrations in the hypothalamus have been shown at their lowest concentration during the winter months. Dietary carbohydrates increase the production of brain serotonin. SAD sufferers crave carbohydrates and feel energized when they consume them.
Antidepressant medications called selective serotonin re-uptake inhibitors, such as Prozac, Zoloft, and Paxil, increase the amount of serotonin available for nerve signal transmission and appear to reverse the symptoms of SAD…as does light therapy.
When SAD was first identified, clinical studies tested the efficacy of light therapy with banks of fluorescent lights and crude “lightboxes” of 2,500 to 5,000 lux (the measurement of light which enters the eye) intensity. Patients would sit in front of these lightboxes for two to four hours. Later research demonstrated that 30 minutes of exposure to 10,000 lux lightboxes provided comparable relief to SAD sufferers. Whereas “fullspectrum” lighting (mimicking the spectral distribution of natural sunlight) was formerly thought to be important, it is now widely dismissed as being unnecessary. More recent studies have pointed to wavelengths around 467 nanometers as best for suppressing melatonin production. What appears to work most effectively is when the level of light produced matches the intensity of outdoor light shortly after sunrise or before sunset. Light intensity is critical for adequate therapy.
As effective as lightboxes were in treating SAD, they were commonly regarded as cumbersome, expensive, obtrusive, and unattractive. Today, light therapy devices, such as the Sadelite and Travelite from Northern Light Technologies, are much more affordable, comfortable to use, attractive, and unobtrusive, while delivering the requisite 10,000 lux of light.
A few companies have begun offering light-emitting devices using light-emitting diodes (LED). Though they offer novel appeal, they are inefficient compared to fluorescent-light technology for two reasons: The amount of heat they produce and the discomfort caused by the afterimage of looking into a matrix of pinpoint lights.
Although the purchase of a phototherapy device does not require a prescription, it is a good idea to consult with a psychiatrist, psychologist, or therapist before submitting to light therapy. Only a healthcare professional can distinguish between SAD symptoms and those caused by other problems that may not be alleviated bylight therapy.
There is a cultural footnote to this engaging new field of chronobiology. We have begun to fathom the mysteries of how our body clocks work, only to realize that we are rediscovering ancient truths.
Celebrating the winter solstice, the shortest and darkest day of the year—December 21st—predates the Roman Saturnalia, which predates Christmas. We celebrate the return of light by lighting candles, dancing, singing, and welcoming the new life that dwells in the darkness. This primordial call found expression in Christmas among Christians, Hanukkah among Jews, and Diwali among Hindus; all festivals of light that celebrate rejuvenation and rededication.
Above all, these festivals promise us ever-brightening days ahead and fortify us through our darkest hours.
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