A recent small-scale study has concluded that hospitalized patients with COVID-19 are less likely to have life threatening complications if they have sufficient vitamin D levels. However, the research has significant flaws.

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A new study concludes that people with sufficient levels of vitamin D are less likely to develop life threatening COVID-19 complications when hospitalized with the disease.

The research, published in the journal PLOS ONE, could be valuable for doctors attempting to reduce the mortality rates of COVID-19 in the absence of an effective vaccine.

If further studies back up these findings, vitamin D supplements might offer a cost-effective way to limit the risk of severe COVID-19. It is important to note, though, that this recent study has several limitations.

Significantly, following discussions on social media, PLOS ONE has released an “expression of concern” regarding the study. Before we outline the research, we will cover some of the primary issues. The journal outline a list of problems. For instance, they write:

“Questions were raised about whether the statistical analyses and results were sufficiently robust to support the article’s conclusions, and about how potential confounds were addressed in the data analyses.”

PLOS ONE also explain that “[t]here are statements in the article, including in its title and conclusions, that suggest a causal relationship between vitamin D levels and the clinical outcome of COVID-19 infections which is not supported by the data.”

The journal also note that less than 1 in 3 participants had laboratory confirmed SARS-CoV-2 infections. The authors of the study also declared no competing interests, which raises another red flag, as PLOS ONE write:

“[P]ublicly available information indicates that corresponding author [Michael F. Holick] may have potential competing interests that include non-financial interests based on his vitamin D research and other activities focused on vitamin D; contributions to an app that tracks vitamin D; and interests that include consultancies, funding support, and authorship of books related to vitamin D usage.”

Since the sudden emergence of the virus SARS-CoV-2 and the disease that it causes, COVID-19, scientists have paid a great deal of attention to the development of a vaccine.

Experts consider a vaccine to be crucial in reducing the effects of the virus, even if it is not yet clear to what extent an initial vaccine would moderate rates of transmission and infection.

Alongside the endeavor to develop a vaccine, researchers are also focusing on developing effective COVID-19 treatments. Even if none can make a person immune to the virus, treatments may be able to reduce the disease’s severity.

The Food and Drug Administration (FDA) have approved two drugs as treatments for COVID-19: remdesivir and dexamethasone.

Another candidate is vitamin D. Research has suggested that it might, in theory, be effective, but corroborating this requires further efforts.

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Rather than analyzing the effects of vitamin D as COVID-19 treatment, the researchers behind the present study looked at the effects of a person’s vitamin D levels on the severity of the disease.

To do so, they analyzed data from patients with confirmed COVID-19 who had been admitted to the Sina Hospital, in Tehran, Iran.

Of the 611 people admitted with confirmed COVID-19 before May 1, 2020, there were records of the 25-hydroxyvitamin D levels, an indication of overall vitamin D levels, for 235 patients. Their mean age was 58.7 years, ranging from 20–90 years, and 37.4% were older than 65.

The researchers classified the patients into two groups: those with vitamin D levels of at least 30 nanograms per milliliter (ng/ml) — an amount considered sufficient by the Endocrine Society — and those with lower values.

They then analyzed the severity of the patients’ COVID-19 signs and symptoms using guidelines from the Centers for Disease Control and Prevention (CDC). Severe or critical disease might involve a range of issues, including shortness of breath, respiratory failure, or a significantly reduced blood oxygen level.

After cross-checking the patients’ vitamin D levels with the severity of their COVID-19 symptoms and accounting for confounding factors, the researchers found that having a vitamin D level of above 30 ng/ml was significantly associated with having less severe COVID-19.

Among the 235 patients with confirmed COVID-19, only 32.8% had sufficient levels of the vitamin.

The researchers also found that the patients with sufficient vitamin D had higher blood lymphocyte counts and lower levels of C-reactive protein in their blood — both of which indicate a positive immune response.

The researchers speculate that this may have reduced the likelihood of developing cytokine storm, which can cause acute respiratory distress syndrome in COVID-19 patients, sometimes resulting in death.

The findings highlight, the researchers say, that vitamin D sufficiency may be important in the eventuality that people develop COVID-19 alongside another respiratory disease, such as influenza.

According to the study’s corresponding author, Dr. Michael F. Holick, director of the General Clinical Research Unit at the medical campus of Boston University, in Massachusetts, “There is great concern that the combination of an influenza infection and a coronal viral infection could substantially increase hospitalizations and death due to complications from these viral infections.”

For the researchers, their findings suggest that vitamin D supplementation would be valuable. As Dr. Holick notes: “Because vitamin D deficiency and insufficiency is so widespread in children and adults in the United States and worldwide, especially in the winter months, it is prudent for everyone to take a vitamin D supplement to reduce [the] risk of being infected and having complications from COVID-19.”

Here, it is perhaps worth reminding ourselves of Dr. Holick’s “potential competing interests,” as outlined by PLOS ONE.

It is worthing noting the present study’s limitations. First, the researchers only had access to a relatively small number of patients. Before drawing solid conclusions, scientists need to carry out much larger studies.

Also, various issues can influence both vitamin D status and COVID-19 severity, such as socioeconomic factors and smoking status. The scientists accounted for neither of these in their analysis.

Additionally, because the study was cross-sectional, the researchers could not prove that vitamin D insufficiency caused an increase in disease severity.

To address these limitations, the researchers call for “large-scale studies and randomized clinical trials.”

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