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This story was updated Oct. 27, 2020 with new studies on vitamin D and COVID-19.

May 18, 2020 -- Could having a healthy blood level of vitamin D help you avoid the intensive care unit and death if you become infected with COVID-19?

More research suggests that the “sunshine vitamin” may play a role in how severe your case may be.

While the studies don’t prove cause and effect, “these studies support the notion that vitamin D might be protective against COVID complications," says Vadim Backman, PhD, a professor of biomedical engineering and medicine at Northwestern University, Chicago. He researched the link between vitamin D deficiency and differences in death rates in different countries.

Among the newest studies:

  • More than 80% of 200 patients hospitalized with COVID-19 had vitamin D deficiency. Patients  with lower vitamin D levels also had higher blood levels of inflammatory markers. But the researchers found no link between low D levels and how severe the disease was.
  • Spanish researchers tested how prescription vitamin D could affect people hospitalized with COVID. Of the 50 who received it, only one needed the intensive care unit (ICU), and none died. Among 26 patients who did not receive the vitamin, 13 needed ICU care and two died.
  • U.S. researchers evaluated blood samples from 235 patients admitted to the hospital with COVID and then followed them to see how they fared. Patients who had adequate vitamin D levels were less likely to become unconscious or die from COVID. (After the study was published, the journal editors published an ''expression of concern," questioning whether the sample size was large enough and how the data was analyzed. The study's author, Michael Holick, MD, a vitamin D researcher at Boston University known for promoting the vitamin, confirmed that a larger study is needed.)   

More studies are coming. Researchers from Queen Mary University of London are launching Coronavit, a 6-month study that will enroll 5,000 people to see if high-dose vitamin D can reduce winter respiratory infections, including COVID-19.

And 31 other studies are listed at Clinical Not all are recruiting yet.

Experts say that healthy blood levels of vitamin D may give a survival advantage by helping people with COVID-19 avoid a cytokine storm, when the immune system overreacts and begins attacking your body's own cells and tissues.

In the meantime, some people say there’s no harm in taking the vitamin as a precaution.

"I feel like if there is anything we can be doing at the moment to support our body, I am totally on board," says Jackie Wilcox, 38, of Newburyport, MA, near Boston. Her family, including her husband and two children, are taking daily supplements.

How Did Researchers Start Looking at Vitamin D?

Vitamin D, produced when the sun hits your skin, has many other benefits, such as bone health. It’s also found in some foods and supplements.

When the COVID-19 pandemic began escalating, Backman, the Northwestern researcher, says he wanted to help but wasn’t sure how. "There were several mysteries still not addressed," he says. One was the difference in death rates from country to country.

So his team did a statistical analysis of data from hospitals and clinics across China, France, Germany, Italy, Iran, South Korea, Spain, Switzerland, the U.K., and the U.S. After looking at likely explanations for differences in the death rates from COVID-19, such as variation in health care quality, age of the population, testing rates, and different virus strains, none held up.

The role of vitamin D in regulating the immune system, including its potential ability to suppress dangerous cytokine production, is well-known. And sunlight and vitamin D had been linked with lowering the death rate in the 1918-1919 influenza pandemic.

So when research on the role of the cytokine storm in COVID-19 emerged, Backman's group focused more on the role of vitamin D levels.

They estimated the association between vitamin D and severe COVID-19 based on a potential link between vitamin D deficiency and C-reactive protein, or CRP, a surrogate marker for severe COVID-19. These proteins are produced by the liver in response to inflammation to lessen the damage from infection, he says.

They estimated that about 17% of patients deficient in vitamin D would get a severe COVID-19 infection, but only about 14%, of those with healthy vitamin D levels. Backman said the difference is statistically significant. "How much it will [actually] lower the mortality, we don't know," he says, because the numbers are based on a statistical model.

    Other Studies Finding a Vitamin D Link

    Among recent studies finding a link between vitamin D levels and how severe COVID-19 is:

    • Researchers from the U.K. evaluated the average vitamin D levels and the number of COVID-19 cases, as well as the death rates, across 20 European countries. Countries with low average vitamin D blood levels in the population had higher numbers of COVID-19 cases and deaths, says study leader Petre Cristian Ilie, MD, PhD, research and innovation director at the Queen Elizabeth Hospital Foundation Trust in King's Lynn, U.K.
    • At Northwestern University, researchers used modeling to estimate that 17% of those deficient in vitamin D would develop a severe COVID-19 infection, but only about 14% of those with healthy vitamin D levels. They estimated the association between vitamin D and severe COVID-19 based on a potential link between vitamin D deficiency and C-reactive proteins, or CRP, a surrogate marker for severe COVID-19
    • In a small study, Louisiana and Texas researchers evaluated 20 patients hospitalized with COVID-19, finding that 11 of the patients admitted to the ICU were vitamin D deficient, but only four of those not needing the ICU.
    • Indonesian researchers evaluated 780 documented cases of COVID-19 and found that most patients who died had vitamin D levels below normal.
    • Irish researchers analyzed European population studies and vitamin D levels, finding countries with high rates of vitamin D deficiency also had higher death rates from COVID-19. Those researchers asked the government to raise the vitamin D recommendations.

    Pre-COVID-19 Research on Vitamin D's Benefits

    While the early research on vitamin D and COVID-19 is just starting, other research has found that vitamin D supplements can help reduce the risk of respiratory infection. And researchers who looked back at the 1918-1919 influenza pandemic found that patients with healthy vitamin D blood levels were less likely to die.

    The research linking vitamin D levels and COVID-19's cytokine storm is in its early stages but not surprising, says Bart Roep, PhD, chair of the department of diabetes immunology at City of Hope, a cancer center in Duarte, CA. Vitamin D, he says, is ''the negotiator" because "it doesn't suppress the immune system, it modulates it. Vitamin D makes the immune cells less inflammatory."

    While research finds that low vitamin D may affect how severe COVID-19 will be, it's not yet known if restoring vitamin D to normal levels would help as a treatment. Nor can anyone say for sure that having a healthy vitamin D level will help you avoid the virus.

    A researcher from the University of Southeastern Philippines evaluated the vitamin D blood levels of 212 people diagnosed with COVID-19 and found the level of vitamin D was lowest in those in critical condition and highest in those with a milder infection. The conclusion of his paper, not peer-reviewed, is that supplements ''could possibly improve clinical outcomes of patients infected with COVID-19."

    "We already know we need it for bone health," says Ilie, the U.K. researcher. "Waiting for the evidence on vitamin D and COVID-19 -- how do I say this -- the evidence may come too late to help."

    But not everyone agrees that vitamin D may be useful in taming COVID-19. Researchers from the Center for Evidence-Based Medicine posted a ''rapid review" of the evidence on May 1, concluding ''There was no evidence related to vitamin D deficiency predisposing to COVID-19, nor were there studies of supplementation for preventing or treating COVID-19."

    The researchers also say that while there is ''overlap" between some groups at risk of being low in vitamin D and groups at high risk of getting COVID-19, including older adults, people of color, and those with chronic diseases, those associations are not proven.

    In a recent peer-reviewed study, researchers who evaluated more than 348,000 people, including 449 with confirmed COVID-19, found no link between vitamin D levels and risk of infection, nor a link that might explain ethnic differences in developing the infection.

    More about Vitamin D

    A simple blood test can detect whether your levels of vitamin D are healthy or deficient. A level of 20 nanograms per milliliter or over is needed to maintain bone health; under 12 nanograms/ml is termed deficient.

    Vitamin D also helps regulate cell growth and reduce inflammation. Some research suggests it could help prevent and treat diabetes, high blood pressure, and blood sugar problems, but the National Institutes of Health views that research as not clear-cut.

    To maintain a healthy blood level of vitamin D, the Institute of Medicine recommends children under age 1 year take in 400 international units (IUs) of vitamin D daily, and people ages 1 to 70 years old take in 600 IUs. People over age 70 should get 800 IUs a day.

    Vitamin D is naturally present in few foods, but it’s added to others and is also available as a supplement. Three ounces of cooked salmon has 570 IUs, while 3 ounces of rainbow trout has 645. A cup of 2% vitamin D-fortified milk has 120.

    But during the pandemic, it may be wise to take more, says JoAnn Manson, MD, DrPH, a professor of medicine at Harvard Medical School and chief of the Division of Preventive Medicine at Brigham and Women's Hospital. "The recommended dietary allowance of vitamin D is 600-800 IU/daily, but during this period, a multivitamin or supplement containing 1,000-2,000 IU/daily of vitamin D would be reasonable," she told Medscape earlier this year.

    Now, Manson is launching a clinical trial to see if a daily supplement of vitamin D for 4 weeks will reduce the risk of hospitalization and/or death in patients newly diagnosed with COVID. She is also studying whether taking it will cut the risk of infection in their closest household contacts. Participants will take 9,600 IUs a day for 2 days, then 3,200 IUs for days 3 through 28.

    Vitamin D toxicity can occur with doses of 50,000 to 60,000 IUs daily, experts say. Too much can lead to a buildup of calcium in the blood, along with vomiting, weakness, frequent urination, and an irregular heartbeat.

    As COVID-19 cases have climbed, Tracy A. Pearson, 45, of Los Angeles, a doctoral student and university employee who also has a law degree, began researching to see what might help reduce her risk, in addition to social distancing and hand-washing.

    She has asthma and is on medication for it. And her lungs can be fragile. "When I get a cold, I get pneumonia, more often than not," she says. She soon found the vitamin D-COVID-19 research and talked it over with her doctor.

    She had had low vitamin D levels in the past, and had gotten back to a healthy level by taking 50,000 IUs weekly, so her doctor, after evaluating her, agreed to do the same again. So she has started taking more than her usual 4,000 IUs a day. She also takes other precautions, such as staying home as her husband handles outside errands. And he also takes 4,000 IUs daily.

    They have continued this throughout the pandemic.

    "I'm a problem solver by nature," Pearson says. "I was trying to figure out how I could mitigate [risk]. It wasn't that I went into the research thinking 'vitamin D.'''


    Show Sources

    Petre Cristian Ilie, MD, PhD, research and innovation director, Queen Elizabeth Hospital Foundation Trust; consultant urological surgeon, Queen Elizabeth Hospital Foundation Trust and Norfolk and Norwich University Hospital, U.K.

    Vadim Backman, PhD, professor of biomedical engineering and medicine; director, Center for Physical Genomics, Northwestern University.

    Bart Roep, PhD, chair, Department of Diabetes Immunology, City of Hope, Duarte, CA.

    Jackie Wilcox, registered dietitian, Newburyport, MA.

    Tracy A. Pearson, doctoral student, university employee, Los Angeles.

    Medscape: "Does Vitamin D Protect Against COVID-19?"

    Aging Clinical and Experimental Research: "The role of vitamin D in the prevention of coronavirus disease 2019 infection and mortality[KD1] ."

    medRxiv: "Vitamin D insufficiency is prevalent in severe COVID-19[KD2] ," "The Possible Role of Vitamin D in Suppressing Cytokine Storm and Associated Mortality in COVID-19 Patients[KD3] ."

    SSRN: "Patterns of COVID-19 Mortality and Vitamin D: An Indonesian Study[KD4] ," "Vitamin D Supplementation Could Possibly Improve Clinical Outcomes of Patients Infected with Coronavirus-2019 (COVID-19[KD5] )."

    Centre for Evidence-Based Medicine: "Vitamin D: A rapid review of the evidence for treatment or prevention in COVID-19."

    Diabetes & Metabolic Syndrome: Clinical Research & Reviews: "Vitamin D Concentrations and COVID-19 Infection in UK Biobank."

    Irish Medical Journal: "Vitamin D and Inflammation: Potential Implications for Severity of Covid-19."

    Dermatoendocrinology: "The possible roles of solar ultraviolet-B radiation and vitamin D in reducing case-fatality rates from the 1918-1919 influenza pandemic in the United States."

    The BMJ: "Vitamin D supplementation to prevent acute respiratory tract infections: systematic review and meta-analysis of individual participant data."

    National Institutes of Health: "Vitamin D: Fact Sheet for Health Professionals."

    Harvard T.H. Chan School of Public Health: "The Nutrition Source: Vitamin D."

    Journal of Investigative Medicine: "Vitamin E and the Immune System."

    Mayo Clinic: "What is vitamin D toxicity? Should I be worried about taking supplements?"  

    The Journal of Steroid Biochemistry and Molecular Biology: "Effect of calcifediol treatment and best available therapy versus best available therapy on intensive care unit admission and mortality among patients hospitalized for COVID-19: A pilot randomized clinical study."    

    PLOS One: "Vitamin D sufficiency, a serum 25-hydroxyvitamin D at least 30ng/mL reduced risk for adverse clinical outcomes in patients with COVID-19 infection."

    Journal of Clinical Endocrinology & Metabolism: "Vitamin D Status in Hospitalized Patients with SARS-Cov-2 Infection."

     Michael Holick, MD, professor of medicine, Boston University

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