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Does Vitamin D Protect Against COVID? Seems Not

It would indeed be nice if simply giving people vitamins could prevent a pandemic. But we must acknowledge that it cannot.

This article was originally published in the Montreal Gazette

One of the major arguments used by people who want to downplay the seriousness of this pandemic or the importance of vaccines is to raise the issue of Vitamin D.

Early in the pandemic some research suggested a link between vitamin D deficiency and severe COVID-19 disease. Some contend that if we simply gave people vitamin D supplements, there would be no need for lockdowns, masks or vaccines because we would effectively eliminate coronavirus and its impact on our lives. If that were true, vitamin D would have saved us all a lot of pain and heartache. Unfortunately it is not.

Over the years, vitamin D has been suggested as a possible treatment for many diseases, including cancer and cardiovascular disease. But when put to the test, it has failed on multiple occasions. The reason the initial results, though encouraging, proved false is an example of how different types of research can answer different questions. The early research was, generally speaking, observational research. In these types of studies, researchers examine data to see if the patients with cancer or heart disease tend to have lower vitamin D levels in their blood than healthy patients do. But the true method to establish whether a treatment works is to do a randomized controlled trial where you take a group of people and randomly give some vitamin D and the others a placebo to see if cancer or heart-disease rates differ in these two groups.

Since you recruit all subjects at the beginning of the study before they get sick and randomly assign them to a treatment or placebo, there should be no differences between the two groups. It was randomized studies that ultimately proved that vitamin D had no impact on cancer or heart disease. But doing randomized studies is hard, time consuming and costly, and there has not been enough time to do many such studies for COVID-19. There is, however, a statistical technique that comes close to mimicking a randomized trial and can help determine if the association between vitamin D levels and COVID-19 severity is real or driven by other factors.

Researchers at McGill recently conducted a Mendelian Randomization study, a type of genetic analysis that is sometimes referred to as nature’s randomized trial. Mendelian randomization studies exploit a particularly useful quirk of genetic inheritance. At conception, an embryo is equally likely to receive either version A or version B of a gene, essentially mimicking the randomization seen in clinical trials. Since genetics at the moment of conception are unaffected by things that happen later in life, in a large random sample both groups should have equal numbers of smokers, diabetics, people with high blood pressure and so on, so any differences between the two groups should be due entirely to Vitamin D levels.

In this analysis, higher vitamin D levels did not reduce the risk of catching COVID-19 or getting more severe disease or landing in hospital. Along with some other recent vitamin D randomized trials, this research argues against vitamin D having any role in terms of treatment or prevention. As the authors themselves concluded, other avenues should be given higher priority.

While many people still cling to the early research linking low vitamin D levels to worse COVID-19 outcomes, it is becoming increasingly clear that much of that association was driven by other factors like age or high blood pressure and that people with low vitamin D do worse because they are sicker on average.

It would indeed be nice if simply giving people vitamins could prevent a pandemic. But we must acknowledge that it cannot. There are more fruitful avenues of research to explore and a much better way to prevent a fourth wave, especially given the growing spread of the Delta variant. That better way is vaccination, because vaccines work and, so far, vitamin D does not.


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