Light can be dangerous. As electromagnetic radiation, light can blind us, burn us, damage our DNA and give us cancer. However, when applied correctly, light might also be able to improve general health and perhaps even slow ageing. The application of visible light to affect cellular biochemistry for health purposes is known as photobiomodulation (PBM). The terms low-level laser therapy (LLLT), cold laser therapy and photobiomodulation are often used interchangeably, though not all PBM involves the use of lasers. While PBM is still largely experimental, it is not pseudoscience. PBM has very real effects on cellular processes that are thought to be fundamental to ageing, and early research suggests that these cellular effects may translate to human health. Let’s take a deep dive into this topic: how exactly does PBM work, how strong is the evidence supporting it, and is the use of PBM for general health justified?
We are exposed to the full spectrum of visible light every day, so what makes PBM special? To understand that, we need to take a trip into the mitochondria, the microscopic power plants that reside within each of our cells. Within each mitochondria, a series of mitochondrial enzymes (creatively named complexes I, II, III and IV) use electrons derived from the breakdown of nutrients in order to generate a tiny voltage across the mitochondrial membrane. This voltage is used to power a fifth mitochondrial enzyme called ATP synthase (AKA complex V). Complex V is the enzyme that produces ATP, the universal fuel source for our cells.
ATP is consumed constantly by cells for all kinds of purposes, from muscle contraction to the repair of damaged DNA. Unfortunately, the efficiency with which mitochondria produce ATP declines with age. This has cascading effects on many aspects of our biology and is thought to be an important driver of age-related diseases.
Now back to PBM: research shows that when mitochondrial enzymes (especially complex 4) absorb certain wavelengths of light, this promotes the shedding of electrons required to generate the voltage powering ATP production. In other words, delivering light concentrated around certain wavelengths can enhance the function of mitochondrial enzymes to boost ATP production, meaning more energy is available for the cell to carry out important tasks. In particular, the rise in ATP activates genes involved in suppressing inflammation and enhancing cellular repair functions.
PBM may also have beneficial effects on the cardiovascular system. ATP production is closely linked to the production of nitric oxide (NO) and reactive oxygen species (ROS). Nitric oxide is important for cardiovascular health as it dilates blood vessels, lowers blood pressure, and preserves the lining of the blood vessels. Large quantities of ROS are generally thought to promote ageing, but smaller increases in ROS may activate cellular repair pathways and lead to a net benefit for health.
The evidence for the effects of PBM is continually growing as interest rises. This database compiled by Vladimir Heiskanen, a prominent PBM researcher, cites nearly 7500 studies investigating the biological effects of PBM. You may notice, however, that the vast majority of these studies were conducted in either cell models or animals, and so we do need to take a measured approach to the human health benefits of this treatment. This isn’t to say that human studies haven’t been done, but they are generally quite small and usually targeted at specific diseases rather than ageing or general health. Furthermore, a lot of research has quality issues, such as failing to use proper placebo control groups. Finally, it’s worth mentioning now that the majority of PBM studies and devices use red or near-infrared light in favour of other wavelengths. As we’ll see later, this is because longer wavelengths of light have a few properties that make them generally more suitable for eliciting health benefits. This means that shorter wavelengths of light are relatively unstudied in humans.
With those caveats aside, what are the proposed human benefits of PBM?
While this is an impressive list, it is important to understand much of this evidence is tentative, and you will find studies both supporting and contradicting some of these benefits. That’s why it’s important to take a cautiously optimistic approach to PBM as more evidence continues to emerge.
Well, if we’re going to get really pedantic about this, then the answer is no. That’s because colour is a property of the visual system. What we really care about is wavelength. To explain why this distinction is important, consider that wavelengths between 620 and 750 nm are considered red, while amber light occupies a much narrower band between 600 and 615 nm, roughly speaking. The only thing that makes this little corner of the electromagnetic spectrum special is that we perceive it as amber. When it comes to the benefits of light applied to the body, there’s no reason amber light should be special in comparison to any other 15nm frequency band. Thus, efforts to pin specific health benefits on specific colours don’t really make a lot of sense outside of the visual system.
With that being said, the wavelength of visible light does influence its interaction with biological tissues. As wavelengths shorten, the depth to which light is able to penetrate biological tissues decreases. Thus, near infrared light can penetrate about 5mm into the skin, reaching deeper structures like subcutaneous fat and hair follicles, while blue light only penetrates around 1mm or less. This generally makes longer wavelengths of visible light more suitable for medical applications and is the main reason most PBM devices use red or near infrared light.
Studies have nevertheless studied the potential advantages of using different wavelengths, as wavelength also influences the likelihood that different molecules will absorb the light, thereby affecting their activity. For example, blue light may be worse at activating those mitochondrial enzymes we talked about, but might be better at activating special light-gated ion channels. Blue light also has antimicrobial properties. Unfortunately, the shorter penetration distance of shorter wavelengths limits the usefulness of their unique properties.
As of yet, there’s not enough human research to confidently say that one wavelength is superior to another for a given condition when applied to the skin. It doesn’t help that varying the intensity and duration of exposure appears to alter the effects of a given wavelength, in some cases resulting in completely opposite effects depending on dosage. Thus, much more human research is needed.
Studies of PBM show it to be safe, with very few side effects. Outside of very high doses or incorrect use of lasers on the eye, PBM appears to be completely safe.
As mentioned already, most PBM devices use red and near-infrared light. The main factors that distinguish different PBM devices are the light source (LED vs laser) and intensity. LEDs are generally present in commercially available PBM devices. They emit divergent light that can cover a large area of skin, but this light has a lower intensity than that emitted by lasers. Laser devices are much more powerful and emit a single, specific wavelength in a focussed beam, making them more efficient but harder to operate. There is no evidence that lasers are inherently better than LEDs, but LEDs may take longer than lasers to deliver a given dose due to their lower intensity. Remember also that the optimal doses and wavelengths for PBM are still being studied.
Photobiomodulation, particularly with red and near-infrared light, shows promise for improving general health, delaying ageing, and in the treatment of multiple age-related diseases. However, a lot of the evidence is quite tentative and we need to see a lot more human research. Different wavelengths of light could have different applications, but it is currently too early to pin specific health benefits on specific wavelengths. Commercially available PBM devices are very unlikely to cause any harm to their user but may also fail to deliver the same benefits as observed in scientific studies, since devices used in research tend to be lasers or more powerful LEDs.
Photobiomodulation with Blue Light on Wound Healing: A Scoping Review https://doi.org/10.3390/life13020575
Photobiomodulation (PBM) research - a comprehensive database https://docs.google.com/spreadsheets/d/1ZKl5Me4XwPj4YgJCBes3VSCJjiVO4XI0tIR0rbMBj08/edit#gid=0
Low-level laser (light) therapy (LLLT) in skin: stimulating, healing, restoring https://www.ncbi.nlm.nih.gov/pmc/articles/PMC4126803/
Changes in Circadian Variations in Blood Pressure, Pain Pressure Threshold and the Elasticity of Tissue after a Whole-Body Photobiomodulation Treatment in Patients with Fibromyalgia: A Tripled-Blinded Randomized Clinical Trial https://doi.org/10.3390/biomedicines10112678
Can transcranial photobiomodulation improve cognitive function? A systematic review of human studies https://doi.org/10.1016/j.arr.2022.101786
Cardiopulmonary and hematological effects of infrared LED photobiomodulation in the treatment of SARS-COV2 https://doi.org/10.1016/j.jphotobiol.2022.112619
Low-intensity LASER and LED (photobiomodulation therapy) for pain control of the most common musculoskeletal conditions https://doi.org/10.23736/s1973-9087.21.07236-1
Opportunities and Challenges of Fluorescent Carbon Dots in Translational Optical Imaging http://dx.doi.org/10.2174/1381612821666150917093232
Title image by Bruno Thethe, Upslash