Photobiomodulation
Melatonin is often referred to as the “hormone of darkness” as exposure to darkness stimulates its production from the pineal gland. Only about 5% of all melatonin produced comes from the pineal gland with the majority of it coming from other tissues and organs, such as the gut mucosa, mitochondria, skin, kidney, thyroid, brain, thymus, spleen, liver, reproductive tissues and all body fluids, as well as what is consumed in the diet, collectively contributing to the body’s melatonin pool (1,2). (Image 1) However, there is evidence that exposure to the major portion of the wavelengths of sunlight, referred to as near infrared radiation (NIR), also promotes extrapineal melatonin production (1,3).
For this reason, photobiomodulation (PBM) therapy (exposure to the sun during the day hours and avoidance of light in the evening and night hours) can be beneficial to the production of melatonin, specifically in the mitochondria, increasing its antioxidant and anti-inflammatory actions, resulting in a host of potential clinical benefits (1,3–7).
Image credit: Tan DX, Reiter RJ, Zimmerman S, Hardeland R. Melatonin: Both a Messenger of Darkness and a Participant in the Cellular Actions of Non-Visible Solar Radiation of Near Infrared Light. Biology (Basel). 2023;12(1):89. Published 2023 Jan 6. doi:10.3390/biology12010089. CC BY 4.0 https://creativecommons.org/licenses/by/4.0/
Humans are exposed to a wide range of solar light (250-4000+ nm). Blue light (visible light) at wavelengths of about 480 nm is most effective for suppressing melatonin synthesis in the pineal gland. However, melatonin produced outside of the pineal gland is not suppressed by this light exposure. In fact, exposure to non-visible NIR (wavelengths of 650-1200 nm) is able to interact with virtually all cells as it penetrates the skin. NIR travels through the cerebral spinal fluid (CSF), amniotic fluid, and blood vessel walls (1). The increased production of melatonin primarily serves as an antioxidant (1,3).
Due to lifestyle factors, such as decreased time and activity outside and Low E glass and artificial lighting in homes, it is reported that 93% of our time is spent without exposure to NIR (1). As part of a comprehensive lifestyle program, daily exposure to sunlight should be recommended, ideally in the morning hours with avoidance during 10 am – 4 pm when ultraviolet radiation is the strongest. It is important to note that for those at risk of skin cancer, protecting the skin from prolonged exposure to sunlight is warranted (8).
References
1. Tan DX, Reiter RJ, Zimmerman S, Hardeland R. Melatonin: Both a Messenger of Darkness and a Participant in the Cellular Actions of Non-Visible Solar Radiation of Near Infrared Light. Biology (Basel). 2023;12(1):89. doi:10.3390/biology12010089
2. Minich DM, Henning M, Darley C, Fahoum M, Schuler CB, Frame J. Is Melatonin the “Next Vitamin D”?: A Review of Emerging Science, Clinical Uses, Safety, and Dietary Supplements. Nutrients. 2022;14(19). doi:10.3390/nu14193934
3. Zimmerman S, Reiter RusselJ. Melatonin and the Optics of the Human Body. Melatonin Research. 2019;2(1). doi:10.32794/mr11250016
4. Lipko NB. Photobiomodulation: Evolution and Adaptation. Photobiomodul Photomed Laser Surg. 2022;40(4). doi:10.1089/photob.2021.0145
5. Chen Z, Huang S, Liu M. The review of the light parameters and mechanisms of Photobiomodulation on melanoma cells. Photodermatol Photoimmunol Photomed. 2022;38(1). doi:10.1111/phpp.12715
6. Odinokov D, Hamblin MR. Aging of lymphoid organs: Can photobiomodulation reverse age-associated thymic involution via stimulation of extrapineal melatonin synthesis and bone marrow stem cells? J Biophotonics. 2018;11(8). doi:10.1002/jbio.201700282
7. Hamblin MR. Mechanisms and applications of the anti-inflammatory effects of photobiomodulation. AIMS Biophys. 2017;4(3). doi:10.3934/biophy.2017.3.337
8. Manne SL, Coups EJ, Jacobsen PB, Ming M, Heckman CJ, Lessin S. Sun protection and sunbathing practices among at-risk family members of patients with melanoma. BMC Public Health. 2011;11. doi:10.1186/1471-2458-11-122