I have been absolutely fascinated with the association of Sun exposure to health for nearly three decades. It was obvious to me that nearly all dermatologists are seriously confused about avoiding the Sun, as Sun exposure is essential to stay healthy.
I always knew there was some important fact we were missing and a video by Dr Roger Seheult (www.medcram.com) elaborates; he explains the ins and outs of how sunlight impacts your health – not only through increasing your vitamin D levels but through melatonin! (Sunlight: Optimize Health and Immunity [Light Therapy and Melatonin]; well worth it).
Seheult’s review is primarily based on a 2020 paper, written by the leading melatonin researcher, Dr Russel Reiter, whom I first heard lecture on melatonin over 25 years ago. This free paper is one of the best I have read in a long while.
Melatonin produced in response to Sun exposure
To summarise the key finding before we dive into the nitty-gritty: the vast majority of the melatonin your body produces – 95% – is actually made inside your mitochondria in response to NIR from the Sun (Fig 1). Only 5% of melatonin is produced in your pineal gland at night.
It is important to note that melatonin supplements, contrary to what you might expect, do not wind up in your mitochondria where they are needed most to quench the damage from oxidative stress produced in the electron transport chain.
Melatonin, of course, is a master hormone, a potent antioxidant and antioxidant recycler, and a master regulator of inflammation and cell death.5 These functions are part of what makes melatonin such an important anti-cancer molecule.
Melatonin has also been shown to be an important part of Covid treatment, reducing incidence of thrombosis and sepsis and lowering mortality. As noted by Seheult, evidence suggests Sun exposure may help combat any number of respiratory infections, including Covid, and the production of melatonin in your mitochondria appears to be a key part of why that works.
Seheult reviews a number of evidence sources showing that Covid rates across the world correlate to the solar index or the amount of Sun striking the area. Positive case rates also correlate with vitamin D levels in the blood. Higher blood levels correlate with lower incidence of Covid and higher rates of survival for inpatients.
In short, vitamin D is more than likely a marker or surrogate for Sun exposure. But nearly all the benefits are likely due to other factors than vitamin D itself. As noted by Seheult, some studies looking at the effect of giving vitamin D to patients treated for severe Covid found no benefit, even at very high doses.
What is more, research looking at UVA levels and Covid mortality rates found areas of the US, the UK and Italy with higher UVA also had lower Covid mortality rates. Vitamin D does not rise in response to UVA (only UVB) so, something in the sunlight, other than stimulating vitamin D, must have a beneficial impact. As noted by the authors:
‘In conclusion, this study is observational and therefore any causal interpretation needs to be taken with caution. However, if the relationship identified proves to be causal, it suggests that optimizing sun exposure may be a possible public health intervention.
‘Given that the effect appears independent of a vitamin D pathway, it suggests possible new COVID-19 therapies and the importance of exploring the role of circulating NO [nitric oxide].”
Here, they speculated that nitric oxide, which is produced in response to UVA, could be the key, as nitric oxide has been shown to limit SARS-CoV-2 replication in vitro in addition to normalising your blood pressure.
But while it is true that nitric oxide rises in response to sunlight (specifically UVA and NIR), Seheult believes the primary mechanism at work here is melatonin, because it is produced in response to the infrared spectrum, which makes up a much greater portion of the solar spectrum than ultraviolet and works regardless of the angle at which it hits the Earth.
Hence the southern part of England can have lower Covid deaths than the northern part, even though the entire country is too far north for vitamin D production during the winter.
Understanding solar energy
As Figure 1 shows, 39% of the solar spectrum is what we see as visible light. The majority of the solar spectrum, 54%, is infrared,11 which is not visible but rather felt as heat. Ultraviolet light accounts for only 7% of the solar spectrum and vitamin D is specifically produced in response to UVB radiation, which is only a small part of the UV spectrum.
Melatonin is produced inside your mitochondria in response to NIR, which is part of the infrared spectrum. Because NIR has a much longer wavelength than UV, it can penetrate much deeper into your body, reaching cells in your subcutaneous tissue and not just on your skin. NIR is not seen but rather felt as warmth. Its penetrative power (heat) also means it can penetrate lightweight clothing.
Melatonin combats oxidative stress, day and night
Your mitochondria produce ATP (adenosine triphosphate), the energy currency of your cells. A by-product of this ATP production are reactive oxidative species (ROS), which are responsible for oxidative stress. Excessive amounts of ROS will damage your mitochondria, contributing to suboptimal health, inflammation and chronic health conditions such as diabetes, obesity and thrombosis (blood clots).
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