Vitamin D Supplements Don’t Seem to Help People Sick With Covid-19

The results of a new clinical trial suggest that vitamin D supplements don’t help people hospitalized with moderate to severe covid-19. Elsewhere, a controversial and preliminary paper that had suggested vitamin D did offer a benefit has now been pulled by the Lancet due to “concerns” over the research design.

Vitamin D has emerged as a new covid-19 panacea for some on social media, displacing past favorites like hydroxychloroquine. There is plenty of evidence that many people could use more daily vitamin D in their lives, especially during the winter. A deficiency in this vitamin, which can be taken as a supplement or synthesized in the skin under strong sunlight, can certainly affect people’s overall health. But the evidence that vitamin D plays a major factor in the severity of covid-19 or that supplementing it could help treat ongoing cases is much less solid.

In late January, a study released on the preprint server SSRN—run by the journal the Lancet—seemed to change that picture. The authors claimed to have found that calcifediol (a byproduct of vitamin D) reduced the risk of mortality in covid-19 patients hospitalized in Spain by a whopping 60% compared to people given standard care. For comparison, the arthritis drug tocilizumab was recently found to reduce mortality in severe covid-19 patients by 4% in a large UK trial—modest results that are promising enough to likely enshrine it as a standard treatment along steroids for critical cases.

But it wasn’t long before outside scientists started to raise issues with those results. For instance, the study’s design was described as both a randomized and an observational study by the authors at different points in the paper—two very different things. Randomized trials, in which some people are randomly assigned to receive a treatment, are considered the gold standard of clinical evidence because they can better confirm that a drug is having a real, beneficial effect on an illness. Observational studies, in which scientists simply observe the differences between groups of people who are getting different care, are important in medicine, but their conclusions are generally viewed with more caution, because it’s harder to know whether a particular treatment actually caused the effect. Other criticisms of the paper included missing relevant data on patients (like some patients’ baseline vitamin d levels), as well as potential statistical flaws. And of course, the findings would be still preliminary no matter what, not having gone through the peer review process yet.

On Friday, the Lancet removed the paper from its preprint server, citing “concerns about the description of the research in this paper.” It also announced that it would launch an investigation into the study.

Meanwhile, the results of what seems to be a genuine randomized trial on vitamin D for covid-19 were published Wednesday in the Journal of American Medical Association—the largest study of its kind to date. Researchers in Brazil said they randomized 240 people with moderate to severe covid-19 in the hospital to receive a single large dose of vitamin D (200,000 IU, compared to the 600-800 IU daily dose recommended for the average adult) or a placebo.

All told, they found no difference in the length of hospital stay between people who took vitamin D and those who didn’t. There was also no difference in the mortality rate or other important metrics, like the likelihood of someone needing invasive ventilation. And while the treatment did appear safe, one patient did have an episode of vomiting likely tied to it.

“The findings do not support the use of a high dose of vitamin D3 for treatment of moderate to severe COVID-19,” the authors wrote.

The JAMA study is still just one trial, and nothing should be decided in medicine on the basis of a single study. And again, too many people aren’t getting as much as vitamin D as they need anyway, so there’s nothing wrong with checking up on your levels with the help of a doctor. But the pandemic has seen countless other potential treatments come and go with little effectiveness to show for it. 

In general, it’s hard to test for the specific effect of vitamin D intake on any condition, because it’s often an indicator of other things. Someone with high vitamin D levels might also be someone who exercises outside often, for instance, and it might be the exercise or their overall good health that’s really providing a protective boost.

If vitamin D does have a benefit for covid-19, it’s likely to be modest at best. And the lack of enthusiasm over this treatment is certainly not evidence of a grand conspiracy in which doctors are downplaying vitamin D just so they can charge for more expensive drugs, as some have suggested. After all, the most successful and lifesaving drug for covid-19 to date is dexamethasone, a generic steroid that can cost less than $10 per treatment.