From the Journals

Low vitamin D linked to increased COVID-19 risk


Implications and future plans

The large number of participants and the “real world,” population-based design are strengths of the study. Considering potential confounders is another strength, the researchers noted. The retrospective database design was a limitation.

Going forward, Dr. Frenkel-Morgenstern and colleagues will “try to decipher the potential role of vitamin D in prevention and/or treatment of COVID-19” through three additional studies, she said. Also, they would like to conduct a meta-analysis to combine data from different countries to further explore the potential role of vitamin D in COVID-19.

“A compelling case”

“This is a strong study – large, adjusted for confounders, consistent with the biology and other clinical studies of vitamin D, infections, and COVID-19,” Wayne Jonas, MD, a practicing family physician and executive director of Samueli Integrative Health Programs, said in an interview.

Because the research was retrospective and observational, a causative link between vitamin D levels and COVID-19 risk cannot be interpreted from the findings. “That would need a prospective, randomized study,” said Dr. Jonas, who was not involved with the current study.

However, “the study makes a compelling case for possibly screening vitamin D levels for judging risk of COVID infection and hospitalization,” Dr. Jonas said, “and the compelling need for a large, randomized vitamin D supplement study to see if it can help prevent infection.”

“Given that vitamin D is largely safe, such a study could be done quickly and on healthy people with minimal risk for harm,” he added.

More confounders likely?

“I think the study is of interest,” Naveed Sattar, PhD, professor of metabolic medicine at the University of Glasgow, who also was not affiliated with the research, said in an interview.

“Whilst the authors adjusted for some confounders, there is a strong potential for residual confounding,” said Dr. Sattar, a coauthor of a UK Biobank study that did not find an association between vitamin D stages and COVID-19 infection in multivariate models.

For example, Dr. Sattar said, “Robust adjustment for social class is important since both Vitamin D levels and COVID-19 severity are both strongly associated with social class.” Further, it remains unknown when and what time of year the vitamin D concentrations were measured in the current study.

“In the end, only a robust randomized trial can tell us whether vitamin D supplementation helps lessen COVID-19 severity,” Dr. Sattar added. “I am not hopeful we will find this is the case – but I am glad some such trials are [ongoing].”

Dr. Frenkel-Morgenstern received a COVID-19 Data Sciences Institute grant to support this work. Dr. Frenkel-Morgenstern, Dr. Jonas, and Dr. Sattar have disclosed no relevant financial relationships.

A version of this article originally appeared on


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