- Vitamin D has been shown to help protect against respiratory infections.
- Vitamin D supplementation may also help reduce COVID-19 infection and severe illness, according to certain observational studies.
- However, recent study using gene variations to replicate a randomised clinical trial reveals that increased vitamin D levels may not protect against COVID-19.
- The research couldn’t rule out the potential that patients who are vitamin D deficient may benefit from supplementation.
The concept of a low-cost, safe, and easily accessible supplement protecting individuals against SARS-CoV-2 infection and severe sickness is appealing.
However, there is conflicting data that vitamin D does protect against COVID-19.
The vitamin is necessary for keeping strong bones and muscles, but there is evidence that it may help protect against respiratory infections.
As a result, it might theoretically defend against COVID-19, which is mostly a respiratory illness.
Another point in its favour is the fact that persons who are prone to vitamin D insufficiency, such as obese people, elderly folks, and individuals of Black or Asian ethnicity, are also prone to COVID-19.
In an unreported investigation, researchers discovered a relationship between mean vitamin D levels in the populations of 20 European nations and the number of COVID-19 cases and death rates.
Several studies have shown a link between low vitamin D levels and COVID-19 infection.
One research indicated that those who were found to be vitamin deficient were more likely to test positive for the virus up to a year later.
The researchers cautioned, however, that only randomised clinical studies might give conclusive proof that vitamin D treatment may prevent COVID-19 and so save lives.
This is due to two statistical issues known as “confounding” and “reverse causation,” which may occur in observational studies like theirs.
When another element that the researchers have not completely accounted for effects the results, this is known as confounding. Older age and chronic illness, for example, increase not just a person’s vitamin D levels but also their risk of COVID-19.
When the result has an effect on the variable being studied, this is known as reverse causation. COVID-19, for example, may cause a person’s vitamin D levels to drop.
Researchers circumvent these issues in clinical trials by randomly assigning people to receive either the medication or a placebo and then monitoring them to see what occurs.
Clinical studies, on the other hand, are expensive and take a long time to produce any results.
Random genetic variation
To explore the effects of vitamin D, researchers from McGill University in Montreal, Canada, and partners from the University of Siena in Italy utilised a method called Mendelian randomisation, which harnesses genetic diversity across persons to imitate a randomised controlled trial.
They started by looking for genetic variations that impact a person’s vitamin D levels.
In fact, a mixture of their parents’ gametes randomly assigns these variations to humans during conception. Because the variations are identified before infection, there are no biases in the results from confounding factors (as the variations may break the links with other confounders) or reverse causation (as the variants may break the correlations with other confounders).
The existence of these variations was subsequently employed as a proxy for vitamin D levels in 14,134 people from up to 11 nations who tested positive for COVID-19 and over 1.2 million people who did not.
They discovered no links between COVID-19 infection, hospitalisation, or sickness severity and projected vitamin D levels based on each person’s genetic composition.
The research was published in the journal PLOS Medicine.
Definitive clinical trials
Professor Naveed Sattar, Ph.D. of the Institute of Cardiovascular and Medical Sciences at the University of Glasgow in the United Kingdom, said, “I guess this paper adds further caution to those who think vitamin D supplements will be a magic bullet against COVID-19, and there are many who still think this.”
Prof. Sattar was not part in this investigation, but he and his colleagues recently published an observational study in which they discovered no link between vitamin D levels and the risk of COVID-19 infection or death.
However, he told Medical News Today that the best way to answer the issue is to conduct vitamin D supplementation clinical studies. Several are already in the works.
“One must always be open-minded about the success of any such trial,” he said. “However, given these new genetic data, combined with our prior work and that of others, I remain pessimistic that vitamin D supplements will provide any meaningful benefit in the prevention or treatment of COVID-19,” he said.
“I might be proved incorrect, but if I am, I will be grateful,” he said.
The authors of the current research warn that they can’t rule out the potential that persons who are vitamin D deficient, rather than those who have inadequate amounts, might benefit from supplementing.
“The reason we can’t say anything about those who are actually vitamin D deficient is because [Mendelian randomisation] looks at average effects,” stated first author Guillaume Butler-Laporte, M.D.
The goal of the study was to look at the impact of average vitamin D levels in a community.
He told MNT that “anytime we look at averages in statistics, there’s a danger that outliers aren’t properly represented.”
He did note out, however, that Mendelian randomisation studies have been shown to be quite excellent at predicting the results of vitamin D clinical trials in other disorders, such as cancer and asthma.
Dr. Butler-Laporte and his colleagues argue in their research that the little funds available for future randomised controlled trials should instead be focused on other possible COVID-19 therapies.
They point out that one of the study’s limitations was that it only looked at people of European origin. It’s still possible that vitamin D levels in other populations have differing impact on COVID-19 results.
Clinical trials of vitamin D supplementation for other diseases, they write, have produced similar results in people of various ancestries.