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“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.” 
– Ray Peat

1. Preface

put on the red lightDuring 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.

Peat doesn’t give many references to justify those claims, but nevertheless, there exists a tremendous amount of study data supporting his views.

Certain wavelengths of electromagnetic radiation directly increase ATP-levels in the tissues, mainly by activating the mitochondrial enzyme cytochrome c oxidase (Cox). The most relevant wavelengths are 600-1000nm–in other words, red light and the penetrating shorter wavelengths of near-infrared radiation (NIR).[1-4]

On the other hand, blue light can inhibit the same enzyme (Cox), and this can lead to retinal damage and other problems.[5,6]

 

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

Red light’s positive effects on health are not a recent finding. The 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.[7]

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.[8, see also Appendix 3]

In this writing, I will focus on the contemporary research, most of which has been usually studied with low-level laser therapy devices (coherent light). Merely during this year (2013), 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 [9]
  • Achilles tendinitis [10]
  • Angina pectoris [11]
  • Aphthous stomatitis [12,13]
  • Body contouring [14,15]
  • Chemotherapy-induced oral mucositis [16-19]
  • Cholesterol levels [20,21]
  • Chronic autoimmune thyroiditis [22,23]
  • Chronic myofascial pain in the neck [24]
  • Chronic rhinosinusitis [25,26]
  • Depression/mood [27-29]
  • Dry mouth / xerostomia [30,31]
  • Dysmenorrea [32]
  • Fibromyalgia [33,34]
  • Gingivitis [35-38]
  • Hand-foot-and-mouth disease [39]
  • Herpes labialis [40-45]
  • Knee osteoarthritis [46-49]
  • Lateral epicondylitis [50]
  • Lymphedema (breast cancer-related) [51,52]
  • Macular degeneration, age-related [53]
  • Male androgenetic alopecia [54,55]
  • Myopia (degenerative/progressive) [56]
  • Onychomycosis [57]
  • Orofacial myofunctional conditions [58]
  • Photoaged skin [59,60]
  • Pressure ulcer [61]
  • Raynaud’s phenomenon [62]
  • Recovery from third molar extraction [63]
  • Restless legs syndrome [64,65]
  • Skin ulcers [66]
  • Sleep quality [67]
  • UVB-induced erythema (prevention of sunburns) [68]
  • Wound healing [69]

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

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

 

3. 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).[53]

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.

 

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.[46]

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.[40]

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. In the placebo group, the symptoms recurred. The median recurrence-free interval in the laser-treated group was 37.5 wk compared with 3 wk in the placebo group.

 

4. 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).[70] 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 enhances the metabolic effect slightly.[71]

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 concentration of anti-inflammatory cytokines increased.[70]

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.[72]

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.[73,74] We could also speculate, whether lack of sufficient therapeutic light could be one cause of the “rT3 dominance” and hypothyroid symptoms. In one study, half of the hypothyroid patients getting near-infrared treatment did not require any medication through the 9-month follow-up after the treatment period, establishing the importance of light for thyroid health.[22]

 

5. 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

 

red light therapyIn 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 was stated long ago by a leading researcher, Tiina Karu, and has been confirmed in a review article by Harvard researchers.[75] 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 to explain 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 lampsincandescent 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 the future 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), because they don’t usually emit significant amount 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.

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.

 

6. 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 probably a 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.[76,77]

Time will tell whether various treatments based on red and near-infrared light will gain popularity in the near future. But they should, because the study results are thoroughly so positive.

 

 

About the author

Vladimir Heiskanen2Vladimir Heiskanen of Finland has been researching and writing about health for several years. Currently a chemistry student at the University of Helsinki and a blogger since 2010, he has a keen interest in human biology, and has studied scores of books, reports and cutting-edge health websites, especially the work of Chris Masterjohn, Paul Jaminet, and Matt Stone. You can read all of his fascinating articles published at 180D HERE.

 

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] Osborne et al: A hypothesis to suggest that light is a risk factor in glaucoma and the mitochondrial optic neuropathies (2008)
[6] Nick Lane: Are mitochondria the alpha and omega of retinal disease? (2006)
[7] Niels R. Finsen: The Red Light Treatment of Small-Pox (1895)
[8] 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)
[9] Aziz-Jalali et al: Comparison of Red and Infrared Low-level Laser Therapy in the Treatment of Acne Vulgaris. (2012)
[10] 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)
[11] Babushkina et al: Results Of 10-Year Use Of Low Intensity Laser Therapy And Conventional Treatment Of Patients With Stenocardia
[12] Anand et al: Low level laser therapy in the treatment of aphthous ulcer. (2013)
[13] De Souza et al: Clinical evaluation of low-level laser treatment for recurring aphthous stomatitis. (2010)
[14] Jackson et al: Low-level laser therapy as a non-invasive approach for body contouring: a randomized, controlled study. (2009)
[15] McRae&Boris: Independent evaluation of low-level laser therapy at 635 nm for non-invasive body contouring of the waist, hips, and thighs. (2013)
[16] Kuhn et al: Low-level infrared laser therapy in chemotherapy-induced oral mucositis: a randomized placebo-controlled trial in children. (2009)
[17] 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)
[18] 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)
[19] Hodgson et al: Amelioration of oral mucositis pain by NASA near-infrared light-emitting diodes in bone marrow transplant patients. (2012)
[20] Jackson et al: Reduction in Cholesterol and Triglyceride Serum Levels Following Low-Level Laser Irradiation: A Noncontrolled, Nonrandomized Pilot Study (2010)
[21] Maloney et al: The reduction in cholesterol and triglyceride serum levels following low-level laser irradiation: a non-controlled, non-randomized pilot study (2009)
[22] Höfling et al: Low-level laser therapy in chronic autoimmune thyroiditis: a pilot study. (2010)
[23] 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)
[24] 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)
[25] Naghdi et al: A pilot study into the effect of low-level laser therapy in patients with chronic rhinosinusitis. (2013)
[26] Krespi&Kizhner: Phototherapy for chronic rhinosinusitis. (2011)
[27] Barrett&Gonzalez-Lima: Transcranial infrared laser stimulation produces beneficial cognitive and emotional effects in humans. (2013)
[28] 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)
[29] Meesters et al: Prophylactic treatment of seasonal affective disorder (SAD) by using light visors: bright white or infrared light? (1999)
[30] Vidović Juras et al: Effects of low-level laser treatment on mouth dryness. (2010)
[31] Lončar et al: The effect of low-level laser therapy on salivary glands in patients with xerostomia. (2011)
[32] Shin et al: Skin adhesive low-level light therapy for dysmenorrhoea: a randomized, double-blind, placebo-controlled, pilot trial. (2012)
[33] 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)
[34] Gür et al: Efficacy of low power laser therapy in fibromyalgia: a single-blind, placebo-controlled trial. (2002)
[35] Obradović et al: Low-level lasers as an adjunct in periodontal therapy in patients with diabetes mellitus. (2012)
[36] Igic et al: Chronic gingivitis: the prevalence of periodontopathogens and therapy efficiency. (2012)
[37] Obradović et al: A histological evaluation of a low-level laser therapy as an adjunct to periodontal therapy in patients with diabetes mellitus. (2013)
[38] Makhlouf et al: Effect of adjunctive low level laser therapy (LLLT) on nonsurgical treatment of chronic periodontitis. (2012)
[39] Toida et al: Usefulness of low-level laser for control of painful stomatitis in patients with hand-foot-and-mouth disease. (2003)
[40] 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)
[41] Muñoz Sanchez et al: The effect of 670-nm low laser therapy on herpes simplex type 1. (2012)
[42] Dougal&Lee: Evaluation of the efficacy of low-level light therapy using 1072 nm infrared light for the treatment of herpes simplex labialis. (2013)
[43] Ferreira et al: Recurrent herpes simplex infections: laser therapy as a potential tool for long-term successful treatment. (2011)
[44] de Carvalho et al: Effect of laser phototherapy on recurring herpes labialis prevention: an in vivo study. (2010)
[45] Eduardo Cde et al: Prevention of recurrent herpes labialis outbreaks through low-intensity laser therapy: a clinical protocol with 3-year follow-up. (2012)
[46] Hegedus et al: The effect of low-level laser in knee osteoarthritis: a double-blind, randomized, placebo-controlled trial. (2009)
[47] 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)
[48] Stelian et al: Improvement of pain and disability in elderly patients with degenerative osteoarthritis of the knee treated with narrow-band light therapy. (1992)
[49] Alghadir et al: Effect of low-level laser therapy in patients with chronic knee osteoarthritis: a single-blinded randomized clinical study. (2013)
[50] Lam&Cheing: Effects of 904-nm low-level laser therapy in the management of lateral epicondylitis: a randomized controlled trial. (2007)
[51] 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)
[52] Ahmed Omar et al: Treatment of post-mastectomy lymphedema with laser therapy: double blind placebo control randomized study. (2011)
[53] Ivandic&Ivandic: Low-level laser therapy improves vision in patients with age-related macular degeneration. (2008)
[54] 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)
[55] Lanzafame et al: The growth of human scalp hair mediated by visible red light laser and LED sources in males. (2013)
[56] Shyrygina&Khadzhieva: [Effect of infrared low-intensity laser therapy on orbital blood circulation in children with progressive short sightedness]. (2009)
[57] Landsman et al: Treatment of mild, moderate, and severe onychomycosis using 870- and 930-nm light exposure. (2010)
[58] Melchior Mde et al: Does low intensity laser therapy reduce pain and change orofacial myofunctional conditions? (2013)
[59] Baez&Reilly: The use of light-emitting diode therapy in the treatment of photoaged skin. (2007)
[60] Russell et al: A study to determine the efficacy of combination LED light therapy (633 nm and 830 nm) in facial skin rejuvenation. (2005)
[61] Schubert V: Effects of phototherapy on pressure ulcer healing in elderly patients after a falling trauma. A prospective, randomized, controlled study. (2001)
[62] Hirschl et al: Low level laser therapy in primary Raynaud’s phenomenon–results of a placebo controlled, double blind intervention study. (2004)
[63] Aras&Güngörmüş: The effect of low-level laser therapy on trismus and facial swelling following surgical extraction of a lower third molar. (2009)
[64] Mitchell et al: Restless legs syndrome and near-infrared light: An alternative treatment option. (2011)
[65] Mitchell et al: Comparison of two infrared devices in their effectiveness in reducing symptoms associated with RLS. (2011)
[66] Kubota J: Defocused diode laser therapy (830 nm) in the treatment of unresponsive skin ulcers: a preliminary trial. (2004)
[67] Zhao et al: Red Light and the Sleep Quality and Endurance Performance of Chinese Female Basketball Players (2012)
[68] Barolet&Boucher: LED photoprevention: reduced MED response following multiple LED exposures. (2008)
[69] 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)
[70] 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)
[71] Barulin&Plavskii: Effect of Polarization and Coherence of Optical Radiation on Sturgeon Sperm Motility (2012)
[72] Bashir et al: UVB and proinflammatory cytokines synergistically activate TNF-alpha production in keratinocytes through enhanced gene transcription. (2009)
[73] Stouthard et al: Effects of acute and chronic interleukin-6 administration on thyroid hormone metabolism in humans. (1994)
[74] van der Poll et al: Tumor necrosis factor: a putative mediator of the sick euthyroid syndrome in man. (1990)
[75] Chung et al: The Nuts and Bolts of Low-level Laser (Light) Therapy (2012)
[76] Paradies et al: Cardiolipin-dependent decrease of cytochrome c oxidase activity in heart mitochondria from hypothyroid rats (1997)
[77] Jakovcic et al: Biochemical and stereological analysis of rat liver mitochondria in different thyroid states (1978)

Jagdeo et al: Transcranial red and near infrared light transmission in a cadaveric model. (2012) “These findings indicate that near infrared light can penetrate formalin fixed soft tissue, bone and brain and implicate that benefits observed in clinical studies are potentially related to direct action of near infrared light on neural tissue.”

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.”

Brown GC: Nitric oxide inhibition of cytochrome oxidase and mitochondrial respiration: implications for inflammatory, neurodegenerative and ischaemic pathologies. (1997) “Nitric oxide (NO) at high levels is cytotoxic, and may be involved in a range of inflammatory, neurodegenerative, and cardiovascular/ischaemic pathologies. The mechanism of NO-induced cytotoxicity is unclear. Recently we and others have found that low (nanomolar) levels of NO reversibly inhibit mitochondrial respiration by binding to the oxygen binding site of cytochrome oxidase in competition with oxygen.”

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.”

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.”
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.“

Wu&Persinger: Increased mobility and stem-cell proliferation rate in Dugesia tigrina induced by 880nm light emitting diode. (2011) “These findings suggest that non-coherent light sources with power-densities about 1000 times lower than contemporary low-power laser settings remain effective in generating photobiostimulation effects and warrants further investigation on stem-cell proliferation induced by near-infrared light emitting diodes.”

Appendix 2: Animal studies (with positive results)

Rats: laryngitisreflux laryngitispalatal mucoperiosteal wound healingbone metabolismperipheral nerve regeneration,acute joint inflammationzymosan-induced arthritistendon healingacute skeletal muscle injuryMetSyn-related kidney injurystreptozotocin-induced diabetic kidneyheart failure-related inflammationcortical metabolic capacity and memory retentiontraumatic brain injuryrheumatoid arthritisacute myocardial infarctionsecond-degree burn healingthird-degree burn healing1 2 3lesions of diabetic retinopathymethanol-induced retinal toxicity 

 
 

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