Beating Seasonal Affective Disorder (SAD)

About half a million Americans — women more often than men — suffer from seasonal affective disorder. Although bright white light remains a mainstay of treatment, in the past few years researchers have investigated ways to improve and refine light therapy.

Traditional light therapy

Fluorescent light boxes are most often used to deliver traditional bright light therapy. Patients usually expose themselves to 30 minutes of light. Bright white light acts on cells in the retina that connect to the hypothalamus, a part of the brain that helps control circadian rhythms, which are somehow disrupted in seasonal affective disorder.

Two reviews of multiple studies on light therapy, which included only randomized controlled trials, concluded that bright light therapy was as effective at treating seasonal affective disorder as antidepressant therapy, and in some cases more effective.

But investigators have sought to improve on traditional light therapy for three reasons. First, it doesn’t work for everyone. Different studies have reported that 50% to 80% of patients achieve complete relief from depressive symptoms after bright light therapy — and remission may depend upon carefully individualized timing of light.

Second, dosing remains a major question. Dose depends on the strength of the light source, the patient’s distance from the light box, light wavelength, and duration of exposure. The recommendation for 30 minutes of daily exposure is based on average response to white light; some patients may not need that much exposure to benefit, or may experience adverse side effects from that amount. Others — such as parents of toddlers — may not be able to sit in front of a device for 30 minutes each morning.

Finally, side effects of bright light therapy, while mild for many patients, may be more of a concern for others. For example, bright light therapy may trigger hypomania or mania in patients with bipolar disorder, which is why mood-stabilizing medications are often recommended at the same time. And while the risk of retinal damage from light therapy is small over all, some medications and medical conditions increase the risk for some patients.

Retina risk The following medications or conditions raise the risk of retinal damage from bright light therapy: First-generation antipsychotics Lithium Melatonin St. John’s wort Diabetes Retinopathies

Enhancing light therapy

Investigations are under way to see if changing the timing of light therapy, or using particular wavelengths of light, might improve response or reduce risk of side effects like mania or retinal damage.

Better timing. Researchers from Columbia University reported that remission from seasonal affective disorder was twice as likely if light therapy was precisely calibrated to melatonin rhythms. They found that 80% of patients achieved remission if light therapy began 7.5 to 9.5 hours after an evening melatonin surge, compared with 38% of patients whose light therapy began 9.5 to 11 hours afterward. Individual melatonin shifts may vary by five to six hours.

Dawn simulation. In this variation of light therapy, a preset light device turns on before a patient awakens. Light intensity increases gradually over a period of 90 minutes. Although the studies so far have been small, they have also been promising.

Blue light. Traditional devices use white light, a mixture of all the colors (such as blue, green, and red) in the visible light spectrum. The use of light-emitting diode (LED) technology has made it possible to create smaller and more portable devices and test specific wavelengths of light.

Studies have found that ganglion cells in the retina are particularly sensitive to blue light, suggesting that this wavelength may powerfully affect circadian rhythms. Researchers are investigating whether blue light might provide the same benefit as white light but with less exposure time — which might reduce risk of side effects in vulnerable patients.

Current guidance

Experts recommend that patients with seasonal affective disorder first try traditional bright white light therapy after awakening. If it does not help or creates bothersome side effects, it may be worth trying antidepressants or one of the alternatives under investigation.

The FDA does not test, approve, or regulate light box devices, so patients considering buying any device should ask about the wavelengths it emits and check to see if it has been used in any reputable research facilities.

-Adapted from: “Beating seasonal affective disorder”, in HEALTHbeat e-mail newsletter, Harvard Medical School, December 23, 2008.

 

12/08