Study: Vitamin D deficiency may be linked to COVID-19 mortality — how a common vitamin could become pivotal


A new study from researchers at Trinity College Dublin has hypothesized that vitamin D deficiency may be linked to higher mortality rates from COVID-19. Published in the Irish Medical Journal, the report analyzed vitamin D levels of older people in countries heavily affected by the coronavirus and found that places with high death rates from COVID-19, including Italy and Spain, also had rates of vitamin D deficiency.

Countries such as Norway, Finland and Sweden, although typically less sun-filled, actually showed lower rates of vitamin D deficiency as well as lower mortality rates from COVID-19. The researchers suggest that “supplementation and fortification of foods” could be why vitamin D is at healthy levels there — and that “optimizing” vitamin D levels elsewhere may prevent serious coronavirus complications.

Vitamin D is critical for bone and muscle health and has shown effectiveness in combating depression. Nicknamed the “sunshine vitamin,” it is naturally produced by the skin when exposed to sunlight, but it can also be absorbed through vitamin-D-rich foods, such as salmon and whole eggs, as well as supplements. Deficiency in this vitamin, which is more common among black people, can lead to problems like bone issues and hair loss and can compromise the immune system.

Multiple studies are now theorizing that there may be a link between COVID-19 and vitamin D deficiency. Here's what you need to know. (Photo: Getty Images)
Multiple studies are now theorizing that there may be a link between vitamin D deficiency and COVID-19. Here's what you need to know. (Photo: Getty Images)

Dr. William Schaffner, an epidemiologist and a professor in the division of infectious diseases at Vanderbilt University, tells Yahoo Life that the research from Ireland is promising but doesn’t prove a causal link between the two. “This study is done from 50,000 feet,” Schaffner says. “These authors have gathered data from clinics in a variety of countries. ... But we haven't done an actual study in patients in a prospective fashion. So it’s an interesting hypothesis, but it’s not a route to either prevention or cure at this point.”

Equally cautious about the study is Dr. Kavita Patel, a nonresident fellow at the Brookings Institution and Yahoo Life medical contributor. “I have no reason to believe that there is some significant association with vitamin D alone and [COVID-19] mortality,” Patel says. “It just doesn’t make sense to me clinically.” That’s not to say, however, that she doesn’t consider vitamin D to be beneficial when it comes to respiratory infections.

“There have been studies in the past around the effects of vitamin D supplementation in decreasing the effects of the influenza virus,” Patel says. “So myself, and many doctors I know, started to give our families and ourselves [vitamin D] supplementation when this pandemic started, not knowing if this would be anything like the influenza virus, but we thought it wouldn’t be harmful.”

One of the studies Patel is referring to is a 2017 global meta-analysis of 25 randomized controlled trials, involving more than 11,000 individuals, which concluded that taking vitamin D supplements daily or weekly could significantly reduce the risk of severe respiratory infections like influenza. For those deficient in vitamin D (i.e., having blood levels below 10 mg/dl), the risk of respiratory infection was cut in half. While no similar research on vitamin D protecting against coronavirus exists, Patel says a randomized controlled trial on its effects is currently underway.

Still, the Ireland study is not the first to provide preliminary analysis suggesting there may be a link between vitamin D and COVID-19 severity. A May 7 analysis, led by researchers at Northwestern University, analyzed hospital and clinic data from countries affected by COVID-19 including China, Iran, Italy, South Korea, Spain, Switzerland, the U.K. and the U.S. It also concluded that countries with high death rates, such as Italy and Spain, were more likely to have patients exhibiting vitamin D deficiencies.

In a statement, the study’s lead researcher, Dr. Vadim Backman, said there is evidence of a “significant correlation” — and that “optimizing vitamin D levels” could be a game changer. “Our analysis shows that it might be as high as cutting the mortality rate in half,” Backman said. “It will not prevent a patient from contracting the virus, but it may reduce complications and prevent death in those who are infected.”

Dr. Amesh Adalja, an infectious disease expert and senior scholar at the Johns Hopkins University Center for Health Security, agrees that the theory is probable. “There's long been an understanding that vitamin D deficiency is underdiagnosed in many countries,” Adalja tells Yahoo Life. “And that vitamin D deficiency does play a role in how the human immune system functions and that correcting vitamin D deficiencies can help with the clinical course of individuals with infectious diseases.”

But Adalja recommends getting things checked out before simply running to the store to buy the nutrient. “I think that you should talk to your doctor about getting tested to see that you are deficient in vitamin D before you take it,” he says. “You don't want to overdose yourself on vitamin D, which can happen.”

Overdosing on vitamin D, Patel adds, is unlikely for those with normal kidney function. But she agrees that the takeaway should be that it could be useful to explore it with your doctor. “Nobody thinks that vitamin D by itself is going to be a miracle cure, so to speak,” says Patel. “But it does seem reasonable — especially based on experiences with other diseases — that it could be useful to both check vitamin D levels and also potentially to supplement, even in healthy people.”

For the latest coronavirus news and updates, follow along at According to experts, people over 60 and those who are immunocompromised continue to be the most at risk. If you have questions, please refer to the CDC’s and WHO’s resource guides.

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