New Study Finds Mixed Results for Vitamin D in COVID Recovery

While vitamin D did not reduce COVID severity, it may help with long COVID symptoms.

Mar. 18, 2026 at 7:00pm

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A major new clinical trial led by researchers at Mass General Brigham in Boston found that high-dose vitamin D supplementation did not reduce the severity of COVID-19 or prevent the virus from spreading to others in the same household. However, the study did suggest a potential benefit for vitamin D in helping patients recover from the lingering effects of long COVID, with 21% of those taking vitamin D reporting persistent symptoms like brain fog and exhaustion two months after their initial diagnosis, compared to 25% in the placebo group.

Why it matters

Since the pandemic's early days, many people have looked to vitamin D as a possible shield against the worst effects of COVID-19. This large, detailed study provides important insights into the potential role of vitamin D in COVID recovery, even if it did not find a clear benefit in reducing acute illness severity.

The details

The Vitamin D for COVID-19 (VIVID) trial followed 1,747 adults in the U.S. and Mongolia who had recently tested positive for COVID-19, as well as 277 of their household members. Patients newly diagnosed with COVID were given a high-dose regimen of 9,600 IU of vitamin D3 for the first two days, followed by 3,200 IU per day for a month. However, this did not reduce the need for medical care or stop the virus from spreading to others in the same home. But when researchers looked at patients' health two months later, they found a promising signal - 21% of the vitamin D group reported persistent long COVID symptoms, compared to 25% in the placebo group.

  • The VIVID trial results were published on March 12, 2026.
  • Participants were followed for four weeks after their initial COVID-19 diagnosis, and then again at the eight-week mark.

The players

Mass General Brigham

The hospital system in Boston that led the VIVID clinical trial on vitamin D and COVID-19.

JoAnn Manson

The senior study author, a professor at Harvard Medical School and chief of preventive medicine at Brigham and Women's Hospital in Boston.

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What they’re saying

“While we didn't find that high-dose vitamin D reduced COVID severity or hospitalizations, we observed a promising signal for long COVID that merits additional research.”

— JoAnn Manson, Senior study author

“Long COVID, which can include symptoms of fatigue, shortness of breath, brain fog, other cognitive challenges and more, continues to significantly impact people's lives.”

— JoAnn Manson, Senior study author

What’s next

Researchers hope to expand this study to even larger groups to see if these signals for long COVID recovery remain consistent across different populations.

The takeaway

While vitamin D did not provide the hoped-for benefits in reducing acute COVID-19 severity, this study suggests it may play a role in helping the body clear the lingering effects of long COVID, an area that merits further research.