Vitamin D: A Low-Hanging Fruit in COVID-19?

What your doctor is reading on

MAY 17, 2020 — The mainstream media was flooded this week with reports speculating on what role, if any, vitamin D may play in reducing the severity of COVID-19 infection.

Observational data comparing outcomes from various countries suggest inverse links between vitamin D levels and the severity of COVID-19 responses, as well as mortality, with the further suggestion of an effect of vitamin D on the immune response to infection.

But other studies question such a link, including any association between vitamin D concentration and differences in COVID-19 severity by ethnic group.

And while some researchers and clinicians believe people should get tested to see if they have adequate vitamin D levels during this pandemic — in particular frontline healthcare workers — most doctors say the best way to ensure that people have adequate levels of vitamin D during COVID-19 is to simply take supplements at currently recommended levels.

This is especially important given the fact, that during ‘lockdown’ scenarios, many people are spending more time than usual indoors.

Clifford Rosen, MD, senior scientist at Maine Medical Center’s Research Institute in Scarborough, has been researching vitamin D for 25 years.

“There’s no randomized controlled trial for sure, and that’s the gold standard,” he told Medscape Medical News, and “the observational data are so confounded, it’s difficult to know.”

Whether from diet or supplementation, having adequate vitamin D is important, especially for those at the highest risk of COVID-19, he says. Still, robust data supporting a role of vitamin D in prevention of COVID-19, or as any kind of ‘therapy’ for the infection, are currently lacking.

Rose Anne Kenny, MD, professor of medical gerontology at Trinity College Dublin, Ireland, recently coauthored an article detailing an inverse association between vitamin D levels and mortality from COVID-19 across countries in Europe.

“At no stage are any of us saying this is a given, but there’s a probability that [vitamin D] — a low-hanging fruit — is a contributory factor and we can do something about it now,” she told Medscape Medical News.


Kenny is calling for the Irish government to formally change their recommendations. “We call on the Irish government to update guidelines as a matter of urgency and encourage all adults to take [vitamin D] supplements during the COVID-19 crisis.” Northern Ireland, part of the UK, also has not yet made this recommendation, she said.

Meanwhile, Harpreet S. Bajaj MD, MPH, a practicing endocrinologist from Mount Sinai Hospital, Toronto, Canada, said: “Vitamin D could have any of three potential roles in risk for COVID-19 and/or its severity: no role, simply a marker, or a causal factor.”

Bajaj says — as do Rosen and Kenny — that randomized controlled trials (RCTs) are sorely needed to help ascertain whether there is a specific role of vitamin D.

“Until then, we should continue to follow established public health recommendations for vitamin D supplementation, in addition to following COVID-19 prevention guidance and evolving guidelines for COVID-19 treatment.”

What is the Role of Vitamin D Fortification?

In their study in the Irish Medical Journal, Kenny and colleagues note that in Europe, despite being sunny, Spain and Northern Italy had high rates of vitamin D deficiency and have experienced some of the highest COVID-19 infection and mortality rates in the world.

But these countries do not formally fortify foods or recommend supplementation with vitamin D.

Conversely, the northern countries of Norway, Finland, and Sweden had higher vitamin D levels despite less UVB sunlight exposure, as a result of  common supplementation and formal fortification of foods. These Nordic countries also had lower levels of COVID-19 infection and mortality.

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