Dear Editor

Once again we read a selective approach to evaluating the role of this autocrine signal in the pandemic. The authors do not acknowledge the primacy of physiology in medicine. The physiological serum 25(OH)D3 is between 100 and 150 nmol/L. To acheive this by supplements requires ca 4000 IU pd or more for the obese and some indivduals. This amount is well within the known physiological maximum production rate in the skin exposed to whole-body summer sunlight (10 to 20,000 IU pd).

The authors also ignore evolution. The vitamin D receptor has a 500 million year evolutionary history, its first role being in regulating innate immunty, our first line of defence against microbes, and one which lyses coronavirus rendering them unviable, a trick that vaccines do not replicate. Innate immune defences are pan-specific.

D3 also acts on adaptive immunity to calm the cytokine storm, although this is unlikely to arise if innate defences are fully D3-primed.

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Re: Vitamin D and covid-19: ignorance of physiology and evolution - The BMJ