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Thomas S. May, M.A.Medical Writer |
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Scientists Debate SAD Story: Does White Light Cure Winter Blues?
Thomas S. May, Medical Writer
Introduction When days shorten and nights lengthen, some of us find just getting out of bed difficult. Those of us who also feel depressed every day and for long stretches of every winter may well suffer from seasonal affective disorder (SAD). According to some scientists, SAD develops because its victims don't get enough sunlight in the winter. These researchers also claim that sufferers can be treated successfully with light therapy--exposing them to bright light for a few hours a week. A number of studies performed in the 1980s and '90s appear to support this idea, showing that light therapy relieves the symptoms of SAD in most patients. But some experts are skeptical of these findings. For example, Domien Beersma, MD, a psychiatrist with the University of Groningen in the Netherlands, argues that it is impossible to know if patients given light therapy improve because of the treatment or simply because they expect to get better from it.
"Testing the effectiveness of light treatment presents a serious problem for researchers," Beersma says, "because a proper placebo [dummy therapy] for light treatment does not exist."
Michael Terman, PhD, a professor of clinical psychology at Columbia University in New York City, agrees. He says light therapy "presents a conundrum" for researchers because "one can always see the difference between the active agent and the placebo."
Placebo Power Even though people taking part in studies can tell the difference between the active (bright light) treatment and the intended placebo treatment (dim red light, for example), they can be led to believe that both treatments are supposed to work equally well. In this way, the researchers can tell whether a positive response is actually caused by bright light or whether it is the result of the "placebo effect." Researchers in the United Kingdom tested this approach and published the results of their study in the April 2001 issue of the British Journal of Psychiatry. The results cast some doubt on earlier positive findings. The investigators chose a dim red light as the placebo, and they made sure that people given this treatment believed it was supposed to work. The researchers told them the treatment had been helpful to other patients in the past.
The data show that both the active treatment (bright white light) and the placebo led to an improvement in SAD symptoms in most (about 60%) of the patients.
The power of the placebo effect on SAD has been demonstrated even more dramatically in a recent experiment conducted by Beersma and his colleagues, who managed to convince their study subjects that light treatment applied to the back of the knee was supposed to help SAD symptoms. After several sessions of light treatment applied to the back of the knee, most of the people in the study reported a gradual improvement in their symptoms. People in the control group (who thought that they had received the same treatment, but had not) showed the same degree of improvement as the others did.
Timing Is Everything Even though the British and Dutch scientists found that dummy treatments can improve SAD symptoms just as well as light therapy, new research suggests that when done a certain way, light therapy works much better than most placebo treatments. In a recent study, Terman and
his colleagues compared the effects of light in the morning and evening on
SAD patients. Those exposed to light in the morning responded best: About
80% of them got better, compared to only about 40% of those exposed to
light in the evening. "The effect of morning light exposure is to advance the [body's] biological clock," Terman says. "Such phase advances appear to be at the heart of the mechanism of action of light therapy." To identify conditions in which light therapy might be most helpful, David H. Avery, MD, and his colleagues at the University of Washington compared the effect of "dawn simulation" to that of steady light in the morning and a fake dawn simulation. In the dawn simulation, SAD patients were exposed to a white light that got brighter gradually over a period of 90 minutes just before they woke up at 6 AM. The fake dawn simulation used a gradually intensifying dim red light. Exposure to a steady bright light for 30 minutes in the morning worked no better than the placebo treatment (fake dawn simulation). Patients exposed to the white-light dawn simulation, however, had significantly more improvement than those exposed to either the steady bright light or the placebo.
"Dawn simulation may work best because it most closely resembles the natural conditions that occur in the summer," Avery says. People can detect the changing light conditions through their eyelids even though they are sleeping, he says.
"The light hits the retina of the eye, and the retinas have direct connections to the suprachiasmatic nucleus of the hypothalamus, which is the 'master clock' inside the brain," Avery says. "And this is how light can reset the body's clock and help relieve depression."
Sidebar: SAD Q&A Who might benefit most from light therapy? People whose symptoms include oversleeping or difficulty waking and people who crave carbohydrates and gain weight in the winter are most likely to respond to light treatment. In full-blown SAD, patients have a major episode of depression--which can last as long as 5 months--each winter. A mental health professional experienced in light therapy should treat this kind of depression. What kind of light works best? Many different light boxes have been devised and manufactured, and most have reached the market without any scientific testing. Any light box you buy should have been tested successfully in peer-reviewed clinical trials. Some other guidelines for buying a light box:
Sidebar: 'Lark' or 'Owl'? Are you a morning person ("lark") or an evening person ("owl")? You can find out by completing a questionnaire at the Web site of the Center for Environmental Therapeutics (www.cet.org/AutoMEQ.htm). The answer can help you find out what the best time for receiving light treatment may be for you.
Thomas S. May is a Medical
Writer. Source: Medscape Health
Reprinted from Medscape Health for Consumers.
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