The Therapeutic Effects of Red and Near-Infrared Light (2013 version)

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-Vladimir





"Penetrating red light is possibly the fundamental anti-stress factor for all organisms. The chronic deficiency of such light is, I think, the best explanation for the deterioration which occurs with aging." - Raymond Peat

1. Preface

During the last summer, I spent quite a lot time reading Ray Peat's articles. In many of his articles, Peat writes that darkness and blue light can be harmful for health, and red light is healthy and even crucial for well-being.

Peat doesn't give many references to justify his claims, but nevertheless, there exists a large amount of study data that seems to support his views. Some of the data is presented is this article.




2. The basic mechanism

Certain wavelengths of electromagnetic radiation directly increase ATP-levels in the tissues, mainly by activating the cytochrome c oxidase (Cox), the mitochondrial respiratory enzyme discovered by Nobel laureate Otto Warburg.[1-4] One important mechanism seems to be the photodissociation of nitric oxide, which can bind to Cox, inhibiting its ability to bind oxygen.[5-8]

The most relevant wavelengths are 600-1000nm --- in other words, red light and the penetrating shorter wavelengths of near-infrared radiation (NIR).[1]

There are important differences in the penetrating power of the different wavelengths. Visible red light doesn't penetrate tissue very well, but near-infrared does that quite well. If near-infrared is directed to the skin, the power seems to decrease 1000-fold by every 2-3 centimetres.[9,10] According to a worm study, even those very small doses seem to have an effect on the cellular level.[11] Later in this article, I will also discuss the issue that some of infrared's effects can also spread by circulation (blood cells).

When it comes to Peat's claims about blue light, high intensities can inhibit the same enzyme (Cox), and this can lead to retinal damage and other problems. I haven't examined the mechanism of inhibition.[12,13]





3. The health effects of red light and near-infrared radiation: The extent of research

Red light's positive effects on health are not a recent finding. The very earliest reports on the topic have been published in the 19th century, the most well-known article being The Red Light Treatment of Small-Pox (1895) by Niels Finsen, who also got the 1903 Nobel Prize in medicine, for his research regarding the health effects of light.[14]

In 1910, John Harvey Kellogg published his 200-page book Light Therapeutics, which included a large amount of information about the therapeutic usefulness of light therapy by incandescent light bulbs and arc lights. According to his book, light therapy can be effectively used for diabetes, obesity, chronic fatigue, insomnia, baldness, cachexia and many other health problems.[15, see also Appendix 3]

In this writing, I will focus on the contemporary research, most of which has been has been usually studied with low-level laser therapy devices (coherent light). Merely during this year, dozens of controlled human studies have been published on this subject. Many of the studies are also placebo-controlled, because low-power near-infrared light is invisible and doesn't emit heat.

According to the studies, many different illnesses can be treated with this kind of light therapy. Many of the results have been very encouraging. Here's a list of some illnesses/problems that could be, according to the studies, effectively treated with red light and/or infrared:

Acne [16]
Achilles tendinitis [17]
Angina pectoris [18]
Aphthous stomatitis [19,20]
Body contouring (weight loss) [21,22,90]
Chemotherapy-induced oral mucositis [23-26]
Cholesterol levels [27,28]
Chronic autoimmune thyroiditis [29,30]
Chronic myofascial pain in the neck [31]
Chronic rhinosinusitis [32,33]
Depression/mood [34-36]
Dry mouth / xerostomia [37,38]
Dysmenorrea [39]
Fibromyalgia [40,41]
Gingivitis [42-45]
Hand-foot-and-mouth disease [46]
Herpes labialis [47-52]
Knee osteoarthritis [53-56]
Lateral epicondylitis [57]
Lymphedema (breast cancer-related) [58,59]
Macular degeneration, age-related [60]
Male androgenetic alopecia [61,62]
Myopia (degenerative/progressive) [63]
Onychomycosis [64]
Orofacial myofunctional conditions [65]
Photoaged skin [66,67]
Pressure ulcer [68]
Raynaud's phenomenon [69]
Recovery from third molar extraction [70]
Restless legs syndrome [71,72]
Skin ulcers [73]
Sleep quality [74]
UVB-induced erythema (prevention of sunburns) [75]
Wound healing [76]

(The treatment methods vary between the studies, and this might explain varying study results.)

Many animal studies have also been contucted (see Appendix 2).





4. The health effects of red light and near-infrared radiation: A few examples of the clinical study results

Age-related macular degeneration

Researchers in the University of Heidenberg conducted a large trial of 200 subjects, in which they medicated elderly people with and without cataracts by near-infrared light (using low level laser).[60]

The intervention group was treated four times during two weeks. Placebo group was given a mock treatment.

Placebo didn't affect subject's vision, but of the patients getting infrared, 95% saw significant improvements in their vision. A large portion of the patients were able to see a few rows lower on the Snellen chart. The improved vision was maintained for 3-36 months after treatment. Four years later, the same researchers got similarly excellent results with amblyopia patients.[87]

Knee Osteoarthritis

Hungarian researchers studied the use of near-infrared light in knee osteoarthritis patients, in a double-blinded placebo controlled trial. Intervention group got infrared treatment on their affected joint twice a week, over a period of four weeks. The placebo group got a similar treatment of 100-fold lower intensity.[53]

In the intervention group, the pain scores were (on a scale from 1 to 10):

- 5.75 before the treatment

- 1.71 after the last treatment session

- 1.18 two months after completing the therapy

In the placebo group, the pain scores were:

- 5.62 before treatment

- 4.13 after the last treatment session

- 4.12 two months after completing the therapy


Labial herpes

The researchers of University of Vienna Medical School studied the usage of red light on labial herpes in a double-blind, placebo-controlled trial.[47]

The subjects were treated in a recurrence-free period. The intervention group were treated for 10 minutes daily for two weeks with visible red light (low-level laser). Placebo group got a similar treatment, but the laser wasn't turned on. The subjects wore masks, so that they couldn't see whether they were given the real treatment.

The patients were instructed to return to the department at the time of symptom recurrence. The median recurrence-free interval in the laser-treated group was 37.5 wk compared with 3 wk in the placebo group.

5. The systemic anti-inflammatory effect

Usually the red/near-infrared is applied locally to the treatable tissue. However, light also has systemic effects which seem to be transmitted mainly by circulation of blood. The researcher Natalya Zhevago has conducted an interesting study, in which the patients got some visible light and infrared to the sacral area (low back).[77] The given light was quite similar to sunlight, except that this light didn't contain UV radiation or blue light, and the infrared portion was polarized. According to one study, polarization of light enchances the metabolic effect slightly.[78]

The subjects' blood was analyzed after the treatment. The results were interesting. Subjects' pro-inflammatory cytokines (TNF-α, IL-6 etc.) were dramatically reduced in the subjects, especially in those with initially high values. Also, the concentrations anti-inflammatory cytokines increased.[77]

A dramatic decrease in the level of pro-inflammatory cytokines TNF-α, IL-6, and IFN-γ was revealed: at 0.5 h after exposure of volunteers (with the initial parameters exceeding the norm), the cytokine contents fell, on average, 34, 12, and 1.5 times[...]

The effects were quite opposite to the typical effects of UV radiation, which increases TNF-α ja IL-6 and other pro-inflammatory cytokines.[79] High sun-exposure is also related to increased IL-6 levels.[80]

In human studies, large doses of IL-6 and TNF-α have been demonstrated to suppress peripheral thyroid hormone metabolism by decreasing T3 and increasing rT3.[81,82] We could also speculate, whether lack of sufficient therapeutic light could be one cause of the "rT3 dominance" and hypothyroid symptoms. In two studies, half of the hypothyroid patients getting near-infrared treatment did not require any medication through the 9-month follow-up after the treatment period, somewhat establishing the importance of light for thyroid health.[29,30] Moreover, in a Russian study (Kovalyova 2002), the diabetic patients' total cholesterol was reduced from 7.98 to 5.31 in one month, a change also seen in thyroid treatments.[88,89]




6. Light sources (laser, LED, light bulbs, heat lamps, sunlight)

"Many people who came to cloudy Eugene to study, and who often lived in cheap basement apartments, would develop chronic health problems within a few months. Women who had been healthy when they arrived would often develop premenstrual syndrome or arthritis or colitis during their first winter in Eugene." - Ray Peat

In the studies conducted in recent years, red light and near-infrared have been studied mostly with coherent (laser) light devices. Some animal studies have also been conducted with light-emitting diodes (LEDs), eg. many of Janis Eells' studies.

Despite the fact that most of the studies used coherent light (laser), the coherence of the light is not a requirement for the therapeutic effects, so other light sources can be used therapeutically too. This has been stated long time ago by a leading researcher Tiina Karu, and has been confirmed in a review article by Harvard researchers.[83] And as mentioned above, J. H. Kellogg has reported the immensely effective therapeutic use of incandescent bulbs as early as in 1910 (see Appendix 3).

When I was writing my Circadian Rhythms essay, I used to think about the possible explanations of the therapeutic effects of walking outdoors. Sunlight can increase the production of vitamin D and it can also suppress melatonin, but now we have a brand new mechanism explains why it's good to spend time outdoors.

A review article on this subject states that in central Europe, the amount of IR-A radiation is limited to 20mW/cm2, which is actually quite a good amount compared to the power of the devices used in the low-level laser studies.[1] On the other hand, the wavelengths aren't optimized (to the absorption peaks) as in the laser studies, and daylight also contains UV radiation and blue light, which might reduce the benefits of red light. It should also be remembered that near-infrared radiation doesn't penetrate through the clothes.

In the indoors, halogen lamps, incandescent lamps and heat lamps are good sources of red and near-infrared light, at least if they're held close enough to the skin. Heat lamps by Philips or Osram have quite a good spectrum with low amount of blue light, but a large amount of their power is emitted as warming IR-B radiation, and only ~12% of the power is emitted as the therapeutic wavelengths (600-1000nm). However, the heat lamps are often high power (up to 250W), so they still emit quite a significant amount of therapeutic wavelengths.

Because of the phase-out of incandescent lamps, it will soon be increasingly difficult to get typical incandescent lamps of sufficient power, so in future the heat lamps might be the most practical choice. It's somewhat sad that the incandescent lamps are going to be replaced with compact fluorescent lamps (CFL), which emit some UV but only low amounts of protective red and near-infrared light. This is the reason why some of the researchers, such as Richard Funk and Alexander Wunsch, who also appeared in the Bulb Fiction documentary, have stated that increase in the CFL usage might be harmful to citizens' eyes.

The possible benefits of infrared saunas aren't usually based on this aforementioned mechanism, because most of the saunas don't emit the therapeutic wavelengths of 600-1000nm. For example, in one infrared sauna study, the sauna emitted infrared in the wavelength range of 5000-1000000 nanometres.[84]

Theoretically, LEDs and lasers with optimized wavelengths would be the best option, but to this date, the products aren't very cheap for the consumers. In theory, the optimal device emits only wavelengths of 700-950nm, so the light would be invisible and wouldn't emit any heat, but still it would produce the therapeutic health benefits by increasing the function of Cox.




7. Conclusion

The important biological effects of red light were known even back in the 19th century, yet very few of the biologists seem to know about those findings nowadays. The knowledge of the physiological effects of light is mainly limited to blue light's effects on circadian rhythm, yet the importance of red and near-infrared light is possibly even an more important topic for the public health.

The general therapeutic usefulness of red light reminds me of the therapeutic uses of thyroid hormone, the topic about which I've written before. This connection is actually quite logical, considering that thyroid hormone also increases Cox activity, by increasing the cardiolipin concentration in the mitochondria.[85,86]

Time will tell whether various treatments or lifestyle interventions based on red and near-infrared light will gain popularity in the near future. But they should, because the most of the study results are very positive*.

(*Note: There are also several trials in which results in the LLLT group were identical to placebo group (no benefit). In many cases, it's mostly about laser parameters (often a very low dose) but some results are also somewhat difficult to explain. I think I will investigate the issue during the summer 2014.)

References

[1] Tiina I. Karu: Multiple Roles of Cytochrome c Oxidase in Mammalian Cells Under Action of Red and IR-A Radiation (2010)

[2] Karu et al: Irradiation with He-Ne laser increases ATP level in cells cultivated in vitro. (1995)

[3] Benedicenti et al: Intracellular ATP level increases in lymphocytes irradiated with infrared laser light of wavelength 904 nm. (2008)

[4] Lapchatk et al: Transcranial near infrared laser treatment (NILT) increases cortical adenosine-5′-triphosphate (ATP) content following embolic strokes in rabbits. (2010)

[5] Huang et al: Biphasic dose response in low level light therapy. (2009)

[6] Brown GC: Nitric oxide inhibition of cytochrome oxidase and mitochondrial respiration: implications for inflammatory, neurodegenerative and ischaemic pathologies. (1997)

[7] Brown GC: Regulation of mitochondrial respiration by nitric oxide inhibition of cytochrome c oxidase. (2001)

[8] Nick Lane: Cell biology: Power games (2006)

[9] Hudson et al: Penetration of laser light at 808 and 980 nm in bovine tissue samples. (2013)

[10] Jagdeo et al: Transcranial red and near infrared light transmission in a cadaveric model. (2012)

[11] Wu&Persinger: Increased mobility and stem-cell proliferation rate in Dugesia tigrina induced by 880nm light emitting diode. (2011)

[12] Osborne et al: A hypothesis to suggest that light is a risk factor in glaucoma and the mitochondrial optic neuropathies (2008)

[13] Nick Lane: Are mitochondria the alpha and omega of retinal disease? (2006)
[14] Niels R. Finsen: The Red Light Treatment of Small-Pox (1895)

[15] John H. Kellogg: Light therapeutics; a practical manual of phototherapy for the student and the practitioner, with special reference to the incandescent electric-light bath (1910)
[16] Aziz-Jalali et al: Comparison of Red and Infrared Low-level Laser Therapy in the Treatment of Acne Vulgaris. (2012)

[17] Bjordal et al: A randomised, placebo controlled trial of low level laser therapy for activated Achilles tendinitis with microdialysis measurement of peritendinous prostaglandin E2 concentrations. (2006)

[18] Babushkina et al: Results Of 10-Year Use Of Low Intensity Laser Therapy And Conventional Treatment Of Patients With Stenocardia

[19] Anand et al: Low level laser therapy in the treatment of aphthous ulcer. (2013)

[20] De Souza et al: Clinical evaluation of low-level laser treatment for recurring aphthous stomatitis. (2010)

[21] Jackson et al: Low-level laser therapy as a non-invasive approach for body contouring: a randomized, controlled study. (2009)

[22] McRae&Boris: Independent evaluation of low-level laser therapy at 635 nm for non-invasive body contouring of the waist, hips, and thighs. (2013)

[23] Kuhn et al: Low-level infrared laser therapy in chemotherapy-induced oral mucositis: a randomized placebo-controlled trial in children. (2009)

[24] Gautam et al: Low level laser therapy for concurrent chemoradiotherapy induced oral mucositis in head and neck cancer patients - a triple blinded randomized controlled trial. (2012)

[25] Antunes et al: Phase III trial of low-level laser therapy to prevent oral mucositis in head and neck cancer patients treated with concurrent chemoradiation. (2013)

[26] Hodgson et al: Amelioration of oral mucositis pain by NASA near-infrared light-emitting diodes in bone marrow transplant patients. (2012)

[27] Jackson et al: Reduction in Cholesterol and Triglyceride Serum Levels Following Low-Level Laser Irradiation: A Noncontrolled, Nonrandomized Pilot Study (2010)

[28] Maloney et al: The reduction in cholesterol and triglyceride serum levels following low-level laser irradiation: a non-controlled, non-randomized pilot study (2009)

[29] Höfling et al: Low-level laser therapy in chronic autoimmune thyroiditis: a pilot study. (2010)

[30] Höfling et al: Low-level laser in the treatment of patients with hypothyroidism induced by chronic autoimmune thyroiditis: a randomized, placebo-controlled clinical trial. (2013)

[31] Gur et al: Efficacy of 904 nm gallium arsenide low level laser therapy in the management of chronic myofascial pain in the neck: a double-blind and randomize-controlled trial. (2004)

[32] Naghdi et al: A pilot study into the effect of low-level laser therapy in patients with chronic rhinosinusitis. (2013)

[33] Krespi&Kizhner: Phototherapy for chronic rhinosinusitis. (2011)

[34] Barrett&Gonzalez-Lima: Transcranial infrared laser stimulation produces beneficial cognitive and emotional effects in humans. (2013)

[35] Schiffer et al: Psychological benefits 2 and 4 weeks after a single treatment with near infrared light to the forehead: a pilot study of 10 patients with major depression and anxiety. (2009)

[36] Meesters et al: Prophylactic treatment of seasonal affective disorder (SAD) by using light visors: bright white or infrared light? (1999)

[37] Vidović Juras et al: Effects of low-level laser treatment on mouth dryness. (2010)

[38] Lončar et al: The effect of low-level laser therapy on salivary glands in patients with xerostomia. (2011)

[39] Shin et al: Skin adhesive low-level light therapy for dysmenorrhoea: a randomized, double-blind, placebo-controlled, pilot trial. (2012)

[40] Gür et al: Effects of low power laser and low dose amitriptyline therapy on clinical symptoms and quality of life in fibromyalgia: a single-blind, placebo-controlled trial. (2002)

[41] Gür et al: Efficacy of low power laser therapy in fibromyalgia: a single-blind, placebo-controlled trial. (2002)

[42] Obradović et al: Low-level lasers as an adjunct in periodontal therapy in patients with diabetes mellitus. (2012)

[43] Igic et al: Chronic gingivitis: the prevalence of periodontopathogens and therapy efficiency. (2012)

[44] Obradović et al: A histological evaluation of a low-level laser therapy as an adjunct to periodontal therapy in patients with diabetes mellitus. (2013)

[45] Makhlouf et al: Effect of adjunctive low level laser therapy (LLLT) on nonsurgical treatment of chronic periodontitis. (2012)

[46] Toida et al: Usefulness of low-level laser for control of painful stomatitis in patients with hand-foot-and-mouth disease. (2003)

[47] Schindl&Neumann: Low-intensity laser therapy is an effective treatment for recurrent herpes simplex infection. Results from a randomized double-blind placebo-controlled study. (1999)

[48] Muñoz Sanchez et al: The effect of 670-nm low laser therapy on herpes simplex type 1. (2012)

[49] Dougal&Lee: Evaluation of the efficacy of low-level light therapy using 1072 nm infrared light for the treatment of herpes simplex labialis. (2013)

[50] Ferreira et al: Recurrent herpes simplex infections: laser therapy as a potential tool for long-term successful treatment. (2011)

[51] de Carvalho et al: Effect of laser phototherapy on recurring herpes labialis prevention: an in vivo study. (2010)

[52] Eduardo Cde et al: Prevention of recurrent herpes labialis outbreaks through low-intensity laser therapy: a clinical protocol with 3-year follow-up. (2012)

[53] Hegedus et al: The effect of low-level laser in knee osteoarthritis: a double-blind, randomized, placebo-controlled trial. (2009)

[54] Gur et al: Efficacy of different therapy regimes of low-power laser in painful osteoarthritis of the knee: a double-blind and randomized-controlled trial. (2003)

[55] Stelian et al: Improvement of pain and disability in elderly patients with degenerative osteoarthritis of the knee treated with narrow-band light therapy. (1992)

[56] Alghadir et al: Effect of low-level laser therapy in patients with chronic knee osteoarthritis: a single-blinded randomized clinical study. (2013)

[57] Lam&Cheing: Effects of 904-nm low-level laser therapy in the management of lateral epicondylitis: a randomized controlled trial. (2007)

[58] Ridner et al: A pilot randomized trial evaluating low-level laser therapy as an alternative treatment to manual lymphatic drainage for breast cancer-related lymphedema. (2013)

[59] Ahmed Omar et al: Treatment of post-mastectomy lymphedema with laser therapy: double blind placebo control randomized study. (2011)

[60] Ivandic&Ivandic: Low-level laser therapy improves vision in patients with age-related macular degeneration. (2008)

[61] Leavitt et al: HairMax LaserComb laser phototherapy device in the treatment of male androgenetic alopecia: A randomized, double-blind, sham device-controlled, multicentre trial. (2009)

[62] Lanzafame et al: The growth of human scalp hair mediated by visible red light laser and LED sources in males. (2013)

[63] Shyrygina&Khadzhieva: [Effect of infrared low-intensity laser therapy on orbital blood circulation in children with progressive short sightedness]. (2009)

[64] Landsman et al: Treatment of mild, moderate, and severe onychomycosis using 870- and 930-nm light exposure. (2010)

[65] Melchior Mde et al: Does low intensity laser therapy reduce pain and change orofacial myofunctional conditions? (2013)

[66] Baez&Reilly: The use of light-emitting diode therapy in the treatment of photoaged skin. (2007)

[67] Russell et al: A study to determine the efficacy of combination LED light therapy (633 nm and 830 nm) in facial skin rejuvenation. (2005)

[68] Schubert V: Effects of phototherapy on pressure ulcer healing in elderly patients after a falling trauma. A prospective, randomized, controlled study. (2001)

[69] Hirschl et al: Low level laser therapy in primary Raynaud's phenomenon--results of a placebo controlled, double blind intervention study. (2004)

[70] Aras&Güngörmüş: The effect of low-level laser therapy on trismus and facial swelling following surgical extraction of a lower third molar. (2009)

[71] Mitchell et al: Restless legs syndrome and near-infrared light: An alternative treatment option. (2011)

[72] Mitchell et al: Comparison of two infrared devices in their effectiveness in reducing symptoms associated with RLS. (2011)

[73] Kubota J: Defocused diode laser therapy (830 nm) in the treatment of unresponsive skin ulcers: a preliminary trial. (2004)

[74] Zhao et al: Red Light and the Sleep Quality and Endurance Performance of Chinese Female Basketball Players (2012)

[75] Barolet&Boucher: LED photoprevention: reduced MED response following multiple LED exposures. (2008)

[76] Simunovic et al: Wound healing of animal and human body sport and traffic accident injuries using low-level laser therapy treatment: a randomized clinical study of seventy-four patients with control group. (2000)
[77] Zhevago&Samoilova: Pro- and Anti-inflammatory Cytokine Content in Human Peripheral Blood after Its Transcutaneous (in Vivo) and Direct (in Vitro) Irradiation with Polychromatic Visible and Infrared Light (2006)

[78] Barulin&Plavskii: Effect of Polarization and Coherence of Optical Radiation on Sturgeon Sperm Motility (2012)

[79] Bashir et al: UVB and proinflammatory cytokines synergistically activate TNF-alpha production in keratinocytes through enhanced gene transcription. (2009)
[80] Levandovski et al: The effect of sunlight exposure on interleukin-6 levels in depressive and non-depressive subjects. (2013)
[81] Stouthard et al: Effects of acute and chronic interleukin-6 administration on thyroid hormone metabolism in humans. (1994)

[82] van der Poll et al: Tumor necrosis factor: a putative mediator of the sick euthyroid syndrome in man. (1990)

[83] Chung et al: The Nuts and Bolts of Low-level Laser (Light) Therapy (2012)
[84] Oosterveld et al: Infrared sauna in patients with rheumatoid arthritis and ankylosing spondylitis. A pilot study showing good tolerance, short-term improvement of pain and stiffness, and a trend towards long-term beneficial effects. (2009)

[85] Paradies et al: Cardiolipin-dependent decrease of cytochrome c oxidase activity in heart mitochondria from hypothyroid rats (1997)

[86] Jakovcic et al: Biochemical and stereological analysis of rat liver mitochondria in different thyroid states (1978)

[87] Ivandic&Ivandic: Low-level laser therapy improves visual acuity in adolescent and adult patients with amblyopia. (2012)

[88] Т.В. Ковалева: Комбинированная лазерная терапия больных сахарным диабетом с дислипидеимей (2002)
[89] Moshkovska&Mayberry: It is time to test low level laser therapy in Great Britain (2005)

[90] Möckel et al: Influence of water-filtered infrared-A (wIRA) on reduction of local fat and body weight by physical exercise (2006)

Appendix 1: Recommended articles (+citations)

Tiina Karu: Multiple Roles of Cytochrome c Oxidase in Mammalian Cells Under Action of Red and IR-A Radiation (2010) 

The Low Level Laser Therapy - LLLT Internet Guide

Healing Light Seminars - Laser Research Library

Wu&Xing: Intracellular signaling cascades following light irradiation (2013)

Hashmi et al: Effect of Pulsing in Low-Level Light Therapy (2010)

Nashville Hair Doctor - Low Level Light Therapy System

Stress reaction in outer segments of photoreceptors after blue light irradiation. (2013)

Rojas&Gonzalez-Lima: Neurological and psychological applications oftranscranial lasers and LEDs (2013)

Rojas et al: Neuroprotective effects of near-infrared light in an in vivo model of mitochondrial optic neuropathy (2008) "superoxide dismutase activities were also increased in NIL-treated subjects in a dose-dependent manner, suggesting an in vivo transcranial effect of NIL."

Light promotes regeneration and functional recovery and alters the immune response after spinal cord injury. (2005) "6% of the power of a 150 mW 810 nm laser was transmitted through all of the layers of tissue between the [adult rat] dorsal skin surface and the ventral side of the spinal cord." "PBM resulted in a significant suppression [...] of IL6 expression at 6 hours post-injury, with a 171-fold decrease in expression of IL6."

Hentschke et al: Low-level laser therapy improves the inflammatory profile of rats with heart failure. (2013) "LLLT reduced plasma IL-6 levels (61.3 %; P<0.01), TNF-α/IL-10 (61.0 %; P<0.01) and IL-6/IL-10 ratios (77.3 %; P<0.001) and increased IL-10 levels (103 %; P<0.05) in the 21 J/cm(2)-HF group. Moreover, LLLT reduced the TNF-α (20.1 % and 21.3 %; both P<0.05) and IL-6 levels (54.3 % and 37.8 %; P<0.01 and P<0.05, respectively)"

Fukuda et al: Infrared low-level diode laser on inflammatory process modulation in mice: pro- and anti-inflammatory cytokines. (2013) "The low-level laser application decreased the TNF-α and IFN-γ release in vivo of spleen mononuclear cells in mice, especially after two exposure sessions. However, there was no modulation of the IL-6 and TGF-β1 release."

Chung et al: The Nuts and Bolts of Low-level Laser (Light) Therapy (2012) "It was originally believed that the coherence of laser light was crucial to achieve the therapeutic effects of LLLT, but recently this notion has been challenged by the use of LEDs, which emit non-coherent light over a wider range of wavelengths than lasers. It has yet to be determined whether there is a real difference between laser and LED, and if it indeed exists, whether the difference results from the coherence or the monochromaticity of laser light, as opposed to the non-coherence and wider bandwidth of LED light."

Eells et al: Mitochondrial signal transduction in accelerated wound and retinal healing by near-infrared light therapy. (2004) "These findings provide a link between the actions of red to near infrared light on mitochondrial oxidative metabolism in vitro and cell injury in vivo. Based on these findings and the strong evidence that mitochondrial dysfunction is involved in the pathogenesis of numerous diseases processes, we propose that NIR-LED photobiomodulation represents an innovative and non-invasive therapeutic approach for the treatment of tissue injury and disease processes in which mitochondrial dysfunction is postulated to play a role including diabetic retinopathy, age-related macular degeneration, Leber's hereditary optic neuropathy and Parkinson's disease."

Kim et al: Near-infrared light and expectancy effects on maximal isokinetic strength performance: a randomized, double-blind, placebo-controlled study. (2006) "Individuals in active conditions were outfitted in NIR light-emitting bandages, T-shirts, and socks[...]"

Havelock Ellis: Sexual Education and Nakedness (1909) "The hygienic value of nakedness is indicated by the robust health of the savage throughout the world who go naked. The vigor of the Irish, also, has been connected with the fact that (as Fynes Moryson's Itinerary shows) both sexes, even among persons of high social class, were accustomed to go naked except for a mantle, especially in more remote parts of the country, until the sevcenteeth century. Wherever primitive races abandon nakedness for clothing, at once the tendency to disease, mortality, and degeneracy notably increases, though it must be remembered that the use of clothing is commonly accompanied by the introduction of other bad habits.“

Lindqvist et al: Avoidance of sun exposure is a risk factor for all-cause mortality: results from the Melanoma in Southern Sweden cohort (2014) "The mortality rate amongst avoiders of sun exposure was approximately twofold higher compared with the highest sun exposure group"

Grimes et al: Sunlight, cholesterol and coronary heart disease. (1996) "the increased concentration of blood cholesterol during the winter months, confirmed in this study, may well be due to reduced sunlight exposure"

Al-Tamer et al: Seasonality of Hypertension (2008) "These results suggest that in areas where significant changes in day temperature and daylight duration exist at different times of the year, blood pressure, serum cholesterol, and HDL-C levels change accordingly in a cycle with higher blood pressure and serum total cholesterol and lower HDL-C values in the coldest season." 

Argani&Javanshir: Seasonal variations of blood pressure in hemodialysis and renal transplant recipients. (2004) "We conclude that [blood pressure] and [body weight] are decreased in warmer seasons in both HD and RTX patients."

University of Milwaukee - Light as medicine? UWM researchers explain how

Mironava et al: The effects of UV emission from compact fluorescent light exposure on human dermal fibroblasts and keratinocytes in vitro. (2012) "The data presented herein confirm that higher than expected levels of UVA and UVC irradiation can be emitted by commercially available CFL bulbs as a result of the limitation of the current production process and the possible physical defects in the bulbs where the phosphorus coating was compromised. Skin cells exposed to the CFL exhibit 25% and 50% attrition for DO33 and CF-29, respectively. For the surviving cells, a significant increase in the production of ROS, and in the case of the CF-29, a decrease in their ability to contract collagen and abnormal migration behavior, are observed and consistent with previous reports of exposure to UVA and UVC radiation.

[...]

Illumination of all cell to incandescent light (where no UV emissions were detected), had no significant effect on proliferation, ROS production, or mitochondrial activity. Taken together, our results confirm that UV radiation emanating from CFL bulbs (randomly selected from different suppliers) as a result of defects or damage in the phosphorus coating is potentially harmful to human skin."

Appendix 2: Animal studies (with positive results)

Rats: laryngitis, reflux laryngitis, palatal mucoperiosteal wound healing, bone metabolism, peripheral nerve regeneration,acute joint inflammation, zymosan-induced arthritis, tendon healing, acute skeletal muscle injury, MetSyn-related kidney injury, streptozotocin-induced diabetic kidney, heart failure-related inflammation, cortical metabolic capacity and memory retention, traumatic brain injury, rheumatoid arthritis, acute myocardial infarction, second-degree burn healing, third-degree burn healing1 2 3, lesions of diabetic retinopathy, methanol-induced retinal toxicity

Dogs: time to ambulation in dogs after hemilaminectomy (14d vs 3.5d), myocardial infarction, sperm motility(!!!)

Mice: traumatic brain injury, myonecrosis induced by Bothrops jararacussu snake venom, experimental autoimmune encephalomyelitis1 2

Rabbits: wound healing, embolic stroke


Appendix 3: Quotes from John Harvey Kellogg's book "Light Therapeutics" (1910) (Google Drive)

Appendix 4: Scientific studies about cytochrome oxidase (Google Drive)

Appendix 5: Ray Peat Quotes: Red Light, Infrared, Light, Darkness (Google Drive)