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Is there proof that vitamin D works against COVID-19? False

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Can vitamin D tablets prevent or cure COVID-19? Despite some enthusiastic advertising and serious research, the Rumour Detector reminds us that no clear results are available yet.  
 
The origin of the rumour 

Finally Confirmed! This message has been shared over 10,000 times on Facebook, generating 65,000 interactions. Blogger Chris Masterjohn is enthusiastic about the results of a Spanish study recently published in the Journal of Steroid Biochemistry and Molecular Biology. 

The study in question exists. It is peer-reviewed and compares 76 patients treated for COVID-19 with a combination of hydroxychloroquine and azithromycin. Fifty of them also received calcifediol, the hormone produced in the liver by vitamin D. We’re not talking about vitamin D3 supplements available over the counter. Most of the patients who received calcifediol avoided intensive care (49 of 50, compared to 13 of 26 for the others). 

The downside  

But contrary to what the blogger claims – he’s a nutritionist who sells vitamins and natural products on his website – the study doesn’t settle the question “once and for all”. Even according to its authors, it’s still very preliminary and larger studies will be needed. There are many reasons for caution, experts responded.  The sample is very small (only 76 patients). The initial vitamin D level is unknown. The degree of severity of COVID-19 isn’t identified. Also, the study’s was imperfectly randomized: the patients who didn’t receive calcifediol were more at risk than the patients who received it.  

A persistent rumour 

This isn’t the first time vitamin D has raised enthusiasm. Since February, fact-checking websites and other media have reminded us that there’s still no evidence that vitamin D can prevent COVID-19. In July, an article circulating on social media presented data from a supposedly German study linking low vitamin D levels to mortality by COVID-19. In fact, this study was conducted by Indonesian researchers. It didn’t establish a cause-and-effect relationship these two factors. That’s because it didn’t consider other risk factors. In other words, it compared two groups of patients whose vitamin D level wasn’t the only thing that differentiated them. Since then, the authors have withdrawn this preprint from their platform. 

The role of vitamin D 

However, scientists are really interested in vitamin D, because it is known to pay an important role in regulating the immune system. Several clinical studies are in progress. In theory, vitamin D could mitigate the inflammatory firestorm that the coronavirus frequently causes in the most serious cases. 

Some epidemiological studies also found that a large proportion of patients infected with COVID-19 had a low vitamin D level. But they didn’t prove a cause-and-effect relationship between these two factors. In a study published on September 3, two American researchers concede that vitamin D deficiencies are associated with other risk factors: age, obesity, chronic diseases. A poor diet, a sedentary lifestyle or smoking results in a low vitamin D level

Germany study published in August made the connection between vitamin deficiency and preexisting conditions that can increase the risk of complications for COVID patients. But the results of the clinical studies are still ending. The authors remind us that several effects of vitamin D on the immune system also occur in combination with vitamin A. Yet vitamin A hasn’t been studied in relation to COVID. 

Having said this, it’s still important to have a balanced vitamin D level. Deficiencies are common in industrialized countries, and the lockdown may have accentuated this problem. An easy way to remedy this is to expose yourself to sunlight for fifteen minute (without sunscreen) a few time a week. Before taking supplements, it’s best to consult your doctor, because too much vitamin D can be toxic. In June, a report in BMJ Nutrition, Prevention and Health noted the importance of considering vitamin D intake in the context of a healthy lifestyle, and not as a “magic bullet” to beat COVID-19. 


This article was originally published on the website of L'Agence Science-Presse (French only).


 

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