WEDNESDAY, March 18, 2026 (HealthDay News) — Since the pandemic’s early days, many people have looked to vitamin D as a possible shield against the worst effects of COVID-19.
Studies have yielded mixed results, with no clear benefit to vitamin D supplementation when it comes to COVID.
But a new major clinical trial suggests that while the supplement may not be a miracle cure for an active infection, it might play help patients avoid the lingering symptoms of long COVID.
The Vitamin D for COVID-19 (VIVID) trial, led by researchers at Mass General Brigham in Boston, is one of the largest and most detailed studies ever conducted on this topic.
Results were published March 12 in The Journal of Nutrition.
For the study, researchers followed 1,747 adults living in the United States and Mongolia, who had recently tested positive for COVID, along with 277 of their household members.
Researchers used weighting to balance test groups by age, sex, race and obesity status. On average, participants were 38 years of age.
Patients who were newly diagnosed with COVID were started on a high-dose regimen right away: 9,600 IU of vitamin D3 for the first two days, followed by a daily dose of 3,200 IU for a month.
Despite these significant amounts, there was no difference in how much medical care was needed between those taking vitamin D3 and those taking a placebo that contained no vitamin in the four weeks following their diagnosis.
Furthermore, the vitamin did not seem to stop the virus from spreading to other people living in the same home.
“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,” senior study author Dr. JoAnn Manson said in a news release. She’s a professor at Harvard Medical School and chief of preventive medicine at Brigham and Women’s Hospital in Boston.
That signal came when researchers looked at the patients' health two months after their initial diagnosis.
In the group that took vitamin D, 21% reported persistent symptoms like brain fog or exhaustion at the eight-week mark. In the placebo group, that number was higher, at 25%.
While the difference was only of "borderline" significance statistically, researchers said it may suggest that vitamin D could help the body clear the virus’s long-term effects more efficiently.
“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,” Manson added.
Researchers hope to expand this study to even larger groups to see if these signals for long COVID recovery remain consistent across different populations.
More information
For more details on how vitamin D affects your immune system, see the National Institutes of Health Vitamin D Fact Sheet.
SOURCES: Mass General Brigham, news release, March 12, 2026; The Journal of Nutrition, March 12, 2026
