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Researchers Aim to Prove Vitamin D Can Reduce COVID-19 Severity and Mortality Risk

yellow vitamin d capsules

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Key Takeaways

  • Vitamin D deficiency has been linked to severe cases of COVID-19 and death from the virus. 
  • A new study is examining whether taking high doses of vitamin D can prevent severe COVID-19 and lower transmission risk.
  • More than 40% of Americans may have low levels of vitamin D. 

Researchers from Brigham and Women’s Hospital in Cambridge, Massachusetts, and the Harvard T.H. Chan School of Public Health are beginning the enrollment process for a study to determine if vitamin D can prevent severe disease and death from COVID-19. 

Since the pandemic began, many physicians and researchers have discussed administering vitamin D to people without COVID-19 in order to prevent the disease and to people with COVID-19 in order to avoid a severe case. The reason? Vitamin D can bolster the immune system.

“We know that vitamin D does boost immune function and also has a role in tamping down inflammation when the immune system goes into overdrive,” lead study researcher JoAnn Manson, MD, DrPH, Chief of the Division of Preventive Medicine at Brigham and Women's Hospital, tells Verywell, explaining the immune system may produce too many inflammatory signals in severe cases of COVID-19.

Manson says doctors have noticed that some people with COVID-19 can have lower-than-recommended levels of vitamin D. “But we don’t know if that is cause and effect, which is why we need to do the study,” she says, adding there is enough data to warrant moving forward with a randomized clinical trial to see if vitamin D supplementation can prevent severe illness in those who have recently tested positive.

For the study, researchers plan to enroll 2,700 participants nationwide: 1,500 newly-diagnosed individuals as well as 1,200 close household contacts. Trial participants will take high-dose vitamin D or placebo for four weeks (9,600 IU/day for the first two days, then 3,200 IU per day from day 3 through day 28). The researchers will then evaluate whether taking the supplement reduces the risk of hospitalization or death for those who have been recently diagnosed with COVID-19 infection. 

The team will also assess whether the vitamin D prevents close household contacts from becoming infected. 

What This Means For You

Vitamin D deficiency could increase the risk of severe disease or death from COVID-19. Ask your doctor if you should have a blood test to check your levels of vitamin D to see if you need a supplement.

Determining Dosage

The vitamin D doses planned for the study are much higher than the currently recommended daily allowance (RDA) for adults 19 years and older: 600 IU daily through age 69. For adults age 70 and older, the daily recommended dose is 800 IU, according to the Harvard School of Public Health. 

Because vitamin D can be dangerous at high levels—including a risk of kidney stones—Manson does not recommend that anyone consider taking high doses of vitamin D without a doctor’s recommendation and supervision. 

“It is reasonable to know whether you have the recommended levels of vitamin D by having your doctor order and review a blood test,” she says.  

If your doctor thinks you are deficient, they may recommend a supplement. You can also get vitamin D from time spent outside in the sunshine and from certain foods, including mushrooms, egg yolks, and oily fish like salmon. 

Vitamin D Deficiency Is Common

Vitamin D deficiency is extremely prevalent in Americans. A 2010 study found as many as 42% of Americans are deficient in the vitamin. For that reason, it can be easy to suggest vitamin D deficiency exacerbates all sorts of health problems.

“Any time you run an epidemiological study related to vitamin D levels, you can by chance find a vitamin D deficiency related to just about anything. It could be cancer, and indeed, it could be COVID-19,” Luis Ostrosky-Zeichner, MD, professor of infectious diseases at UT Health in Houston and a spokesman for the Infectious Diseases Society of America, tells Verywell. “Having said that, we do know that vitamin D is an important immune system regulator and associated with risk for respiratory infections. There is also a mechanism of action that may have something to do with [the COVID-19] virus.”

What we know for sure, Ostrosky-Zeichner says, is that people with severe COVID-19 tend to have low vitamin D levels upon hospital admission, and people with higher levels generally do better. 

“[The Brigham] trial is exactly what we need to be doing to find out if there is a crossover relationship between vitamin D and outcomes of the disease,” Ostrosky-Zeichner says.

The information in this article is current as of the date listed, which means newer information may be available when you read this. For the most recent updates on COVID-19, visit our coronavirus news page.

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  1. Forrest KY, Stuhldreher WL. Prevalence and correlates of vitamin D deficiency in US adults. Nutr Res. 2011 Jan;31(1):48-54. doi:10.1016/j.nutres.2010.12.001