Vitamin D is a fat-soluble vitamin, synthesised primarily in the skin when exposed to sunlight. The production of this vitamin varies greatly by region and season, and depending on skin pigmentation. It boosts intestinal absorption of calcium and phosphates, and promotes bone mineralisation.

It is also thought to act on the immune system, generating a certain amount of interest in its potential use in covid-19. Epidemiological studies have shown a statistical association between certain infections and low blood levels of vitamin D, but there is no solid evidence of a causal relationship, or of the value of vitamin D supplementation in these situations.

A few studies have found low levels of vitamin D in the blood of patients infected with Sars-CoV-2, and a statistical association with complications of covid-19. As of mid-December 2020, according to the Belgian Centre for Pharmacotherapeutic Information (CBIP) and our own literature search, the only published results are from a single randomised "pilot" trial, without blinding, in 76 patients (> HERE and > HERE). This pilot was conducted in preparation for a larger trial that appears to have been abandoned. Despite the apparent efficacy of vitamin D in the pilot trial, no other results have confirmed this effect. As of 14 December 2020, the international clinical trials registry clinicaltrials.gov includes about 10 phase 3 clinical trials evaluating vitamin D in Sars-CoV-2 infection, but no results have been published.

In practice, as of late 2020, in the absence of comparative clinical data of sufficient quality, the effect of vitamin D supplementation in preventing infection with Sars-CoV-2 or treating covid-19 remains unknown. Vitamin D can cause adverse effects, especially after an overdose, in particular hypercalcaemia and its complications, which include kidney stones and renal failure. The clinical situations in which the use of vitamin D supplementation is supported by evaluation data remain unchanged, i.e. for the prevention or treatment of bone disorders, mainly in older patients and in some children.

©Prescrire 15 December 2020

Source:

• "Covid-19 et vitamine D : trop d'incertitudes" Application Prescrire 15 December 2020.

For more information:

• "Covid-19: Follow Prescrire's independent, evidence-based analysis of the pandemic" > HERE