Red light phototherapy (2/3): Brain, Muscles and Eyes

Read Time: 8 min

Before writing these posts I was aware of only a fraction of the therapeutic benefits of red light. I have been staggered at how many different effects have now been demonstrated (hence the need for a three-part post)
Since writing the first post I have uncovered a ton of material on red light phototherapy effects on the brain (surely, you are thinking, that’s one place where the sun don’t shine?) plus the latest ideas on how exactly red light pulls off these remarkable feats – it’s to do with water… Consequently, I have rejigged the planned content of post 2 and 3 to fit in these fascinating ideas… enjoy!
Part 1: Skin (click to read)
• Red light and skin rejuvenation, collagen production and wrinkle reduction
• Red light protects the skin from photo-ageing
Part 2: Brain, Muscles and Eyes (this post)
• Red light and brain health
• Red light enhances muscle performance and exercise recovery
• Red and infra-red light protect the retina
Part 3: Hair regrowth, Pain, Wound Healing and Practical Ideas (coming soon)
• Red light increases hair regrowth
• Red-light for pain relief
• Red-light for wound healing
• Practical ways to make use of these ideas

PART 2 INTRODUCTION
In part 1 we looked at the effects of red light on the skin. But does red light penetrate deep enough to affect hair follicles, blood vessels or muscles? The image below indicates the relative depth of penetration of different colours of light. As the diagram shows red wavelengths penetrate most deeply. The image is a little deceptive, as the 830nm wavelength shown on the left of the diagram is actually in the near infrared and invisible to the human eye. Interestingly, if the wavelength is increased further into the mid-infrared it has less penetration, indicating that the human body is most transparent to far-red and near-infrared wavelengths.

As you can see red light easily reaches hair follicles and subcutaneous blood vessels. But can it affect deeper tissue such as muscles? And what about the brain? Surely the skull prevents red light having any direct effects on the brain? Well, let’s see.
Although the diagram above would suggest that red light only penetrates a few millimetres there is, in fact, no sudden cutoff and the intensity simply diminishes as it goes deeper. The image on the right makes it clear that light can pass through more than a 1cm of flesh – a finger in this case. You can check this yourself by holding a bright LED (such as your phone torch function) against your finger [see more here]. Or put a torch in your mouth in a dark room – your whole lower face lights up! (OK, you probably don’t need to do this as most of us tried it when we were seven years old.) This shows that light can penetrate deeply into tissue. But surely it can’t get through bones such as the skull?
Red light for brain health
Amazingly, light shone up the nose actually reaches the brain. Here is an image from a 2013 conference paper The potential of intranasal light therapy for brain stimulation [pdf]

What is constantly amazing about all the areas of research on red-light therapies is the relatively short duration of exposure and the safe, low power levels of the light sources. This makes it all very applicable for home use, using potentially simple equipment that could be employed whilst relaxing or watching TV. There is nothing complex required to apply red or infra-red light via the nose, as indicated in the following photo which comes from the paper above.

Why shine light via the nose? (1) The skull is thinnest at the top of the nasal cavity (2) The shape of the brain behind the nasal cavity means that a large surface area is illuminated (3) Important metabolic regulatory areas such as the hippocampus lie close to this area and can be influenced.
From their studies on the optimum wavelengths for stimulating neurons, the authors developed this small nasal light source using pulsed infrared light. Whilst this is (to my knowledge) not available as a commercial unit, it is easy to find cheap red light nasal clips marketed for hay-fever reduction (yet another red light phototherapy application!) Whilst this may not be as effective as the pulsed IR units, the research base on red light and brain health would suggest it is still very likely to be effective.
Existing evidence of brain stimulation based on intranasal light therapy at red wavelengths 
The paper above starts by covering early research that used red light, before going on to look at the more effective infra-red wavelengths. In those red light studies, the light was applied intranasally, typically for 30 minutes per day for ten days. Benefits were seen in multiple conditions including:

1. Insomnia
2. Mild Cognitive Impairment
3. Alzheimer’s disease
4. Parkinson’s disease
5. Schizophrenia
6. Migraine and headaches
7. Stroke (cerebral infarction)
8. Traumatic brain injury

How does it work?
Circa 2000, it was discovered that the brain contains light-sensitive cells (!) However, it soon became clear that chief effect of red light is on the mitochondria, the cell’s powerhouses, which are stimulated to produce more ATP – the molecule that provides the energy for all cells in living things.
So how does red light stimulate ATP production? Until recently it was assumed to be due to the red light being absorbed by the respiratory enzyme cytochrome C. Then in 2015, Andrei Sommer’s team at the University of Ulm in Germany found that red light interacts with water inside cells. Their research indicates that red and infra-red light exposure reduces the surface tension of water inside cells, making it less viscous, and enabling the mitochondrial membrane enzyme, ATP Synthase*, to run more easily, so producing more ATP. You can read more about this fascinating story over at New Scientist.
(ATP synthase is the smallest electrical rotary motor in the universe! To see it in action take a look at this video on YouTube)
Many of the neurological conditions listed above have recognised links to mitochondrial deficiencies, so it makes sense that red-light therapy can help. Improved mitochondrial functioning can also be induced by a ketogenic diet, and through exercise – both of which also have recognised benefits in these neurological conditions.
The knock on effects of enhanced mitochondrial function are summarised in the following diagram. (If you don’t care much for this level of detail, skip over it!)

Mitochondrial function, of course, is not only relevant to the nervous system but particularly muscle cells which have some of the highest concentrations of mitochondria, which brings us to…
Red light enhances muscle performance and exercise recovery

Red light exposure is known to increases mitochondrial activity, ATP production and protein synthesis. It has therefore been tested for its ability to increase sports performance and exercise recovery, with very positive results.
A meta-analysis in 2013 looked at ten double-blind studies and concluded that,

Exposing skeletal muscle to single-diode and multidiode laser or multidiode LED therapy was shown to positively affect physical performance by delaying the onset of fatigue, reducing the fatigue response, improving postexercise recovery, and protecting cells from exercise-induced damage. [ref]

Observed improvements included increased muscle contractions before exhaustion, reduced lactate formation and a reduction in the inflammatory markers creatine kinase and C reactive protein (CRP). [ref] These effects were induced following just 30 seconds of high intensity red and infra-red LED exposure to the centre of the tested muscle prior to exercise, that’s right, just a 30 seconds exposure!
Two points to note are 1) The red light exposure needs to be before exercise, and 2) as muscle is deeper than skin, either high-intensity red-light sources are needed, or longer exposure periods with regular intensity light sources. Infra-red light, however, has been shown to increase muscle recovery after exercise [ref1, ref2]

Red and infra-red light protect the retina
Red light is now being investigated for the treatment of eye disorders such as macular degeneration, diabetic retinopathy, and amblyopia, among many others. Animal studies of bright-light retinal damage (i.e. blindness induced by really bright light!) found that subsequent stimulation with low dose red light for as little as 90 seconds five times over 35 days helped restore function, whilst similar exposure before the ‘blinding light’ reduced the severity of the damage. [ref]
That’s pretty remarkable, isn’t it?

In a diabetic rat model, whole body red light exposure for 4 minutes per day for 9 weeks led to multiple improvements in retinopathy, including lowering ganglion cell death and reversing the diabetes-induced inflammatory state of the retina. In a more recent human study, four diabetic patients with diabetic macular oedema had one eye treated with red light through the closed eyelid. The other eye served as control. The macular thickness in the treated eye increased by 20% whereas the untreated eye only increased by 3%
In another rat study red light significantly reduced methanol-induced blindness, opening the possibility of a treatment for methanol poisoning which can otherwise lead to permanent blindness [ref]
At the other end of the spectrum – quite literally – lifetime blue light exposure is now considered to be one of the principal causes of Age-related Macular Degeneration (AMD). The increased use of fluorescent lighting in buildings and computer screens may explain the increasing rates of AMD, which is expected to affect 25% of the Western populations by the time they reach the age of 75.
Dietary eye-protection
One of the best natural defences (apart from avoiding blue light sources) is egg yolks. The carotenoids lutein and zeaxanthin, which give egg yolks their distinctive colour, accumulate in the retina and absorb up to 95% of blue light before it reaches the retina [ref]. A 2013 review on diet and eye health concluded that ‘egg yolk could be an important dietary source to improve lutein and zeaxanthin status for the prevention of cataracts and AMD in adults’ [ref].
If you are not into eggs, then either (1) get into eggs or (2) ensure you get sufficient vegetable source carotenoids. Somewhere in our childhoods we all picked up the ‘carrots help you see in the dark’ meme. Carrots, along with many fruit and veg contain these important retinal carotenoids lutein and zeaxanthin. The problem is that being fat-soluble their bioavailability depends on the fats consumed with them. Egg yolk comes with built-in fats, but kale, carrots and broccoli don’t, so the fats in your meal determine how much of these you absorb. This led to a recent headline:

Olive oil and coconut oil could stop you going blind, says nutrition expert in boost for ‘Mediterranean Diet’. The Mirror, July 2016 

However, in another study researchers found that saturated fats (coconut and butter) were more effective than MUFA and PUFA dominated sources (olive oil and fish oils) [ref] as they formed smaller myceles (fat globules) that allowed increased absorption of lutein and zeaxanthin.
So, all in all, it looks like eating eggs is clever, putting butter on your vegetables is great and taking a morning and evening stroll or jog might be wise too.
Next Post (coming soon)
In the final post in this series, we will look at the NASA research that kicked off modern red-light therapy demonstrating its benefits for pain reduction. Plus its benefits in wound healing and hair regrowth.
Finally, we will consider simple practical ways we can apply these ideas in our homes.