Light therapy can help to manage pain

BY MOHAB IBRAHIM, UNIVERSITY OF ARIZONA

Light has been recognized as having biological effects, and scientists are beginning to understand that some of these effects may help to alleviate a variety of chronic conditions, both physically and psychologically. The sleep cycle, for example, is tightly associated with increased and decreased light. Some psychiatric conditions are known to be affected by the brightness of light, and exploiting this connection for treatment purposes could improve the quality of life for many.

Seasonal affective disorder, for example, is a condition in which people may feel loss of the sense of pleasure or lack of energy when they live in areas with decreased sunshine. One potential solution for such individuals is bright light therapy. I am an associate professor of anesthesiology and pharmacology at the University of Arizona (UA) College of Medicine, and I have recently been involved in light therapy studies.

My brother Wael gets occasional headaches. He noticed they would subside when he spent time in his backyard garden tending his trees. Now he prefers being among trees when he has a headache, rather than taking medication to manage it.

It wasn’t until I had a similar experience that I wanted to look into this interesting phenomenon scientifically. I developed a headache, and when I sat in a park, I noticed that my headache lessened. The first question that came to my mind was: What potential impact do chemicals released from trees have on pain?

So my initial impulse was to collect air samples from the park and analyze which chemicals may be released from the trees. But an air sample taken from an open environment will most likely contain many chemicals. Testing each and every one of those chemicals would have required significant time and resources. There had to be a better way.

I asked myself: What do my brother’s backyard in San Diego and the park I frequented in Tucson, Ariz., have in common? Well, the color green is in both places. So perhaps green light is producing analgesic effects.

I started experimenting in my laboratory by exposing healthy rats to various wavelengths of light and testing their responses. Much to my delight and surprise, rats that were exposed to green light for eight hours a day for two to four days exhibited antinociception (higher tolerance to noxious stimuli). We evaluated the rats’ behavioral response to noxious stimuli by measuring both the time before they moved away from a thermal source and the amount of mechanical force applied before they moved away from it. The response of the rats was so dramatic, I had to repeat the experiment several times to make sure the data was real and reproducible. Green light exposure in rats had similar efficacy as NSAIDs and even some opioids, resulting in some rats reaching the cutoff value — the maximum amount of stimulus that can be applied — without exhibiting any signs of discomfort.

My colleagues and I found that exposure to green light also controlled the discomfort associated with many conditions, such as HIV-induced neuropathy in rats. The National Institutes of Health’s National Center for Complementary and Integrative Health granted us an award to conduct a study to further understand the mechanism of green-light pain control.

While we were working with animals to understand the mechanisms of green-light therapy, we decided to move next to clinical trials involving human subjects. After all, green light is relatively noninvasive, and we use low energy from an LED source, so the risks are low. We obtained approval from the Institutional Review Board at UA to work with chronic pain patients.

We recruited patients with fibromyalgia, migraines, and interstitial cystitis who did not respond to traditional therapy. Some patients were seen at the Banner-University Medical Center Tucson pain clinic; some were from the Tucson community; and some were from outside of the city. We started patients on white light as a control for 10 weeks, and then switched to green light. The patients were given multiple paper surveys to evaluate several aspects of their chronic pain at various stages of the process.

White light did not offer much benefit for most of the subjects. However, most study participants loved how green-light therapy made them feel. They reported decreased frequency of headaches, and decreased intensity of their headaches or fibromyalgia. They also reported improved quality of sleep and better quality of life. In fact, many patients refused to return their green light to the researchers after the conclusion of the trial. It was a very good sign that some people with fibromyalgia and migraines felt significantly better after the treatment, in terms of experiencing improved ability to function and lessened intensity of pain.

We still do not fully understand the mechanism by which green light produces its effects. But given that it has low risk and potential benefits, we see advantages in continuing to investigate the option of offering patients a complementary therapy to make their lives more enjoyable.

One thing is clear: Light has more potential to alter biology than we thought. It is time to let it shine in more areas.

Meet the author

Mohab Ibrahim, M.D., Ph.D., earned master’s and doctorate degrees in pharmacology and toxicology from the University of Arizona, with a focus on neuropathic pain. He received a medical degree from the UA College of Medicine in 2008, and completed his residency in anesthesiology from the Brigham and Women’s Hospital in Boston. Ibrahim then earned a fellowship in chronic pain management from the Department of Anesthesiology at Massachusetts General Hospital. He is currently an associate professor of anesthesiology, pharmacology, and neurosurgery at the Banner-University Medical Center Tucson, where he is also the director of the chronic pain clinic.

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