Patients hospitalized with COVID-19 who have sufficient levels of vitamin D show significant reductions in severe outcomes and a lower risk of death compared with insufficient levels, new research shows.

“This study provides direct evidence that vitamin D sufficiency can reduce the complications including the cytokine storm and ultimately death from COVID-19,” said senior author Michael F. Holick, MD, PhD, of Boston University School of Medicine, Massachusetts, in a press statement from his institution.

The research examines hospitalized patients with severe COVID-19 in Iran, and Holick worked with lead researcher Zhila Maghbooli, MD, of the Tehran University of Medical Sciences, and colleagues, on the study, which was published in PLoS One.

The findings come on the heels of another recently published study, in which Holick and his team found that people with sufficient vitamin D levels in the United States had as much as a 54% reduced risk of getting infected with COVID-19.

Although this latest research adds to a plethora of data on the potential role of vitamin D in COVID-19, many questions and caveats remain, commented E. Michael Lewiecki, MD.

“This study adds to an accumulation of data showing an association between higher serum levels of vitamin D and better outcomes in patients infected with COVID-19,” he told Medscape Medical News.

“There is biological plausibility for benefit of vitamin D, since it is known to regulate innate and adaptive immunity in ways that might reduce the viral load in patients exposed to SARS-CoV-2 and mitigate the severity and consequences of cytokine storm.”

“However, it is important to recognize that associations reported in observational studies do not necessarily mean there is a causal relationship,” cautioned Lewiecki, of the University of New Mexico School of Medicine in Albuquerque.

“It may be that higher vitamin D is a marker of better health and lower baseline risk of complications of COVID-19.”

Although Iran Is Sunny, Prevalence of Vitamin D Deficiency Is High

In the latest study published in PLoS One, which involved 235 patients hospitalized with COVID-19 infection in Tehran, Iran, through May 1, 2020, most patients (67.2%) had insufficient vitamin D levels, defined as serum 25-hydroxyvitamin D [25(OH)D] levels < 30 ng/mL.

“Iran is a sunny country but the prevalence of vitamin D deficiency is high especially in elder people who present with more severe clinical manifestations after exposure to SARS-CoV-2,” note Maghbooli and colleagues.

The mean age of those included was 58.7 years, and 37.4% were 65 years or older.

Overall, 74% of patients had severe COVID-19 infection, defined according to the Centers for Disease Control and Prevention criteria.