Laser and LED phototherapy bear further exploration.

Thousands of clinical studies, of varying quality, support the use of cold laser therapy to relieve pain and swelling and to stimulate healing. "Laser therapy is an umbrella term that can include light from low level lasers as well as superluminous diodes, also known as light emitting diodes (LEDS)," explains Kendric C. Smith, PhD, founder and first president of the American Society for Photobiology. Lasers emit coherent waves of a single wavelength. Light from a handheld laser (with a wavelength of 830 nanometers and power of 90 milliwatts) can penetrate up to 5 centimeters below the skin's surface and stimulate all types of cells. LEDs, which cost less than lasers, emit noncoherent light. Light from LEDs does not penetrate as deeply but works very well on surface injuries. Recent studies indicate that wavelength, not coherency, is the therapeutic factor.

But how does light cause a physiological effect? Smith says, "When a photon is absorbed by a molecule, the electrons of that molecule are raised to a higher energy state. This excited molecule must lose its extra energy, and it can do this either by re-emitting a photon of longer wavelength (i.e., lower energy than the absorbed photon) as fluorescence or phosphorescence, it can lose energy by giving off heat, or it can lose energy by undergoing photochemistry." That change in chemistry causes biological effects.

Smith voices his concern that phototherapy will remain outside mainstream medicine and science if the quality of published studies does not improve. Too many studies ignore photobiology fundamentals. Research must identify the system or cellular part that is absorbing specific wavelengths. This "first law of photochemistry," according to Smith, says: "Unless light of a particular wavelength is absorbed by a system, no photochemistry (or photophysics) will occur, and no photobiological effects will be observed, no matter how long one irradiates with that wavelength of light." Each chemical compound absorbs varying amounts of specific wavelengths--the absorption spectrum. For example, Tiina Karu, PhD, showed that respiratory chain molecules (such as cytochrome c oxidase) in the mitochondria absorb visible and near-infrared radiation. She then found that radiation absorption increases cellular metabolism, which sends signals to other parts of the cell and spurs growth. After tracking photon absorption and noting the photobiological effect, the next step is to identify specific wavelengths that produce the desired effect with the least dose. Details like these have potential for moving cold laser therapy from an imprecise pain reliever to a standardized treatment for many common health problems. To further this field, clinical studies need to state the exact wavelength(s), power, dose, area of exposure, pulsed or continuous wave, and time--all the factors that would allow replication of the study by others. Without these specifics, the "paper is useless," says Smith

The effect of light therapy depends on the physiology of the cells themselves. If the body is dealing with a fresh wound, adding light will do little; light does not turn the cells into super cells that exceed their normal response. If, however, a wound is not healing at a normal rate, the correct wavelength(s) can stimulate healing. Too much radiation can actually be counterproductive: "At high doses an excessive amount of singlet oxygen can be produced, and its chemical action can be detrimental to cells," Smith explains.

Alexandra K. Schnee, DC, offers other warnings in her online Low Level Light Therapy series. She says that cold laser therapy should not be directed at the thyroid gland, the eyes, or any lesion suspected of being cancerous. Also, low level light therapy is contraindicated in pregnant women simply because its effect on the fetus is unknown.

Karu TI. Cellular mechanisms of low-power laser therapy (photobiomodulation) [web page]. Available at: www.laserhealthsystems.com/Dr.%20Tiina%20Karu%20Presentation.htm. Accessed September 5, 2009.

Schnee AK. Cold laser therapy advantages and disadvangages [web page]. Spine-Health. February 12, 2009. Available at: www.spine-health.com. Accessed August 17, 2009.

--. Cold laser therapy pain management treatment [web page].Spine-Health. February 12, 2009. Available at: www.spine-health.com. Accessed August 17, 2009.

--. Types of conditions treated by cold lasers [web page]. Spine-Health. February 13, 2009. Available at: www.spine-health.com. Accessed August 17, 2009.

Smith KC. Laser and LED therapy is phototherapy [web page]. American Society for Photobiology. April 30, 2009. Available at www.pol-us.net/lllt/phototherapy.html. Accessed August 17, 2009.

briefed by Jule Klotter

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