(  PDF )  Rev Osteoporos Metab Miner. 2022 ;14(Supl 1): S2-3

Sosa Henríquez M

Editor

Vitamin D is recently in the news. Until not many years ago, it was almost exclusively related to bone mineralization. However, the increasingly widespread knowledge that the actions of vitamin D extend to practically all our body cells has led to the discovery and research into the so-called “extra-osseous effects of vitamin D.” This research is increasing and becoming better known[1-8]. In fact, vitamin D should be termed hormone D, since its structure, functioning, control and self-regulation mechanisms are more typical of a hormone than a vitamin9.
Precisely one of these extra-osseous effects is the direct relationship of hormone D with the functioning of the cells responsible for the body’s immunity. Thus, low levels of vitamin D have been associated with a higher prevalence of infections and autoimmune diseases and adequate levels have been related to a better clinical course of infectious diseases[1,10,11].
The whole world is immersed in the COVID-19 pandemic. This has brought about profound changes in both the social sector and, of course, in health care. We have not yet overcome it completely, although everything indicates that, at the time of this writing (October 2021), we are close to overcoming at least its worst stage, thanks to the greater knowledge of the disease and, above all, to the development of vaccines.
In this sense, Dr. Olmos Martínez’s article, which opens this supplement, offers a masterful overview of the changes that this pandemic has engendered at all levels, especially in the health sphere. Next, Professor del Pino Montes analyzes the mechanisms by which vitamin D exerts its action in the immune system and, therefore, in close relation to infections. Subsequently, Dr. Hernández Hernández reviews the association between vitamin D and COVID-19 infection, which he does with the authority of having published a study carried out by his working group in the Journal of Clinical Endocrinology and Metabolism[12] which was the most read and cited journal article in 2020. Finally, Dr. Gómez de Tejada describes those documents and guides prepared by some scientific societies and institutions in which they reflect on the need of having and obtaining adequate levels of vitamin D to prevent and treat COVID-19.
However, a certain ambiguity prevails concerning vitamin D. It is spoken of in general terms and its different metabolites, cholecalciferol, calcifediol and calcitriol are treated indistinctly, calling them all “vitamin D”, seeming equivalent and similar in terms of potency or toxicity, which is not true[13]. On the one hand, cholecalciferol is the most widely used molecule in the vast majority of clinical trials in which vitamin D has been used as a treatment[14]. In virtually all randomized clinical trials comparing drugs that reduce fracture risk, both the treated and control groups received cholecalciferol. Not one of these trials used calcifediol or calcitriol[15]. Therefore, the clinical evidence goes hand in hand with cholecalciferol.
Furthermore, these molecules do not have the same potency. Calcitriol is so powerful and entails a risk of hypercalcaemia, that its indications approved by the Spanish Agency for Medicines and Health Products (AEMPS) are very scarce, and, in addition, it requires medical inspection approval. Calcifediol is more potent than cholecalciferol and although it does not require inspection, the AEMPS published an alert due to some reported cases of overdose and hypercalcaemia[16]. These side effects, however, do not appear with cholecalciferol.
To sum up, I consider that this collection of articles is of great interest because it deals with a very current topic such as vitamin D in preventing and treating COVID-19, which will help clinicians to gain a better understanding of this broad, complex world of vitamin D.

Conflict of interest: The author declares that he has no conflicts of interest.

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