Michael R. Hamblin
This paper is a review of the Redox Theory of the effects of photobiomodulation (PBM).
The discussion applies to both red light and near-infrared at low power PBM therapy.
There are two hypotheses as to how PBM works.
Hypothesis 1: The Redox Theory is that light is absorbed in the mitochondria at the cytochrome C oxidase (CCO).
Inhibitory nitric oxide disassociates from CCO. This increases the mitochondrial membrane potential.
Hyposthesis 2: PBM activates gated ion channels through a heat and/or a light pathway.
Laser Medicine that Does Not Use Lasers
The term “laser medicine” became an inaccurate when researchers were able to achieve the same effects with non-laser lights.
Lower power light-emitting diodes (LED) can create the same mitochondrial and healing changes as higher-powered laser lights.
LLLT as Low Level Laser
Journal authors first renamed “laser medicine” to “low level laser therapy.” That would be fine, if an LED were a low-level laser, but it is not. Lasers emit coherent waves. LED emits incoherent waves. Calling an LED a “low level laser” just confused the issue.
LLLT as Low Level Light
Recognizing that LEDs are not low-level lasers, authors changed LLLT to mean “low level light therapy.”
Now there were two problems. First, previous authors used LLLT to refer to low-level lasers. When searching scientific journal databases, LLLT would bring up both laser and LED studies. LLLT had two meanings, which confused the issue for researchers.
Next, “low level light therapy” now completely drops “lasers,” which is not what we are trying to say.
We are trying to describe the use of light in medicine, whether that light comes from LED or laser sources.
Photobiomodulation: Using Light to Change Biology
A few light and laser medical organizations agreed. In 2016, they officially changed laser medicine, low-level laser therapy, and low-level light therapy, to Photobiomodulation (PBM).
PBM is the use of photons (light) energy to change (modulate) biology.
Photobiomodulation is over 50 years old. Researchers first applied the concepts to wound repair.
Researchers initially found success using 694 nm and 633 nm wavelengths. Both wavelengths are red. Repeatedly, researchers found frequencies in the red (and infrared range) to heal human and animal biology. Red Light Therapy (RLT) is the use of red and infrared light to heal. RLT is a form of Photobiomodulation.
Laser and LED Effectiveness
Clinicians and consumers can treat scores of problems with light. Researchers have repeatedly found LED to be as effective as lasers. Lasers are more powerful, and take less time to deliver their effective dose.
Clinicians use both laser and LED devices. Consumers use LED only. Lasers can burn, and so are not consumer devices.
Laser and LED lights are equally effective. Laser is more powerful, so treatments are faster. LED is cooler, and so treatments are slower, but consumers can do them at home.
Photobiomodulation Success and Safety
Over 1,000 clinical studies show that PBM is healthy and generally very safe.
PBM is a Goldilocks therapy. The dose must be just right, or the recipient will not get a healing response.
This is because Photobiomodulation has a “biphasic dose response,” that follows the “Arndt-Schulz Law.”
The biphasic dose response means that:
- a little bit of energy works a little bit or not at all
- too much energy works a little bit, not at all, or causes harm
- the healing dose of energy is in a sweet spot between too little and too much
- the effectiveness plateau is a range of energy in the sweet spot, and all energy levels in that range have healing effects
The First Law of Photobiology
For PBM to be effective, the chromophore molecules in the mitochondria must absorb the photons. This is the first law of photobiology.
For example, when the chromophore molecules absorb red nm (nanometer wavelength) photons, the molecules initiate a chain reaction that disassociates nitric oxide, leaving the mitochondria with more oxygen. This gives the body more energy.
The chromophore’s ability to absorb light changes with the light’s wavelengths. Therefore, some wavelengths are more effective than others are.
The mitochondrial oxygen creates a healthful response in skeletal muscle, cardiac muscle, neurons, liver cells, kidney cells, and more.
PBM Redox Increases Energy and Absorbs Oxidants
PBM affects reactive oxygen species (ROS). We usually think of ROS as free radicals, but PBM can use them as messenger transports.
Light in the blue color range has the greatest ROS impact, because it induces ROS creation without reducing their impact.
Red light induces ROS but resolves their presence before they can harm the body.
When red light produces reactive oxygen species, the mitochondria absorb them. Red light increases energy (ATP), which gives the body’s system energy to heal. The red light absorption process invokes N-acetylcysteine, which in turn, reduces reactive oxygen species.
Thus, red light produces free radicals, but disarms them. Red ROS are mediators.
Blue light produces free radicals, and at least in some cases, those reactive oxygen species harm the body.
Biphasic Dose Response
PBM can both heal and harm. Dose quantity and frequency determine the biological response.
For example, 780 nm at 50 J cm^2 (infrared light delivered in 50 joules per square centimeter) increases bone tissue to positively act on osteoporosis and fractures that failed to heal.
On the other hand, 650 nm at 50 J cm^2 (red light delivered in 50 joules per squared centimeter) decreases bone tissue, making both osteoporosis and joint failures worse.
PBM has a protective effect at multiple levels. For example, 670 nm (red) LED reduces methanol damage and potassium cyanide neural damage. When the tissues are exposed to 670 nm light prior to cyanide exposure, the cyanide cannot kill as many cells (the light reduces the apoptosis).
“Photobiomodulation (PBM) involves the use of red or nearinfrared light at low power densities to produce a beneficial effect on cells or tissues. PBM therapy is used to reduce pain, inflammation, edema, and to regenerate damaged tissues such as wounds, bones, and tendons.” – Dr. Michael R. Hamblin