Green light exposure is emerging as a potential therapy for chronic pain conditions like migraines and fibromyalgia, offering a non-pharmacological alternative for patients seeking relief. Researchers at the University of Arizona and other institutions have been investigating the pain-relieving effects of green light, with promising results from both animal and human studies. These findings suggest that green light could provide a safe and effective way to manage chronic pain, addressing a significant unmet need in pain management.
Clinical Evidence for Green Light Therapy
Clinical trials have demonstrated the potential benefits of green light therapy for migraine and fibromyalgia patients. In one study, migraine patients exposed to green light reported a significant reduction in headache days, decreasing from an average of 7.9 to 2.4 days in those with episodic migraines and from 22.3 to 9.4 days in those with chronic migraines. The intensity and duration of headache attacks were also reduced. Similarly, fibromyalgia patients experienced a nearly 60 percent reduction in pain intensity on a numeric scale following green light exposure. These trials involved patients sitting in front of an LED strip emitting green light for one to two hours daily over a ten-week period. No side effects were reported by participants in either trial.
An independent pilot study on fibromyalgia explored the use of green-light filtering glasses, with patients wearing them for at least four hours per day. While the results were not statistically significant, there was a hint at reduced daily opioid requirements among those wearing green glasses. These findings, led by Padma Gulur at Duke University, suggest that easily adaptable methods of green light exposure could offer some benefit.
Rami Burstein's team at Harvard Medical School, studying migraine-related photophobia, found that green light exacerbated headache pain less than other colors. Their research indicated that green light even reduced pain intensity in 20 percent of participants. A larger open-label trial involving 181 individuals showed that two hours of exposure to a green light lamp during migraine attacks improved headache perception in 55 percent of reported events.
Mechanisms of Action
Researchers are actively investigating the mechanisms through which green light exerts its analgesic effects. Evidence suggests that the visual system plays a crucial role. Studies on rats with opaque contact lenses showed no response to green light therapy, indicating that light perception through the eyes is necessary for the therapy to work. While the specific roles of cones, rods, and intrinsically photosensitive retinal ganglion cells (ipRGCs) are still being debated, there is growing consensus on the neural pathways involved.
Yu-Qiu Zhang and colleagues at Fudan University identified a subset of neurons in the ventrolateral geniculate nucleus (vLGN) in the thalamus as key to green light's pain-relieving effects. These neurons express proenkephalin, a precursor to enkephalin, an endogenous opioid involved in pain modulation. Mohab Ibrahim's team also observed increased expression of enkephalins in the spinal cords of rats exposed to green LEDs. Based on these findings, researchers believe that green light activates photoreceptor cells in the eyes, leading to retinal projections that reach the vLGN, activating enkephalinergic neurons, which in turn project to pain-modulating brain areas, increasing the release of enkephalins and other endogenous opioids.
Future Directions
While the precise mechanisms are still being elucidated, the positive impact of green light on patients, the absence of reported side effects, and the affordability of the therapy are encouraging. Researchers are now focusing on optimizing therapy parameters, such as the optimal doses and wavelengths, and identifying other pain conditions that may benefit from green light therapy. Further research is also needed to fully understand the roles of different photoreceptor cells and neural pathways involved in green light's analgesic effects.
Padma Gulur, who has a patent pending for green light-based analgesia, emphasizes the importance of advancing the science, stating, "Once you start seeing this benefit, it behooves us to advance the science."
