Vitamin D may reduce risk of long COVID, study suggests

A randomized trial by Mass General Brigham found that vitamin D supplementation was associated with a small difference in reported lingering symptoms eight weeks after infection (21% vs. 25%) and did not change short-term illness severity or healthcare visits.

Researchers at Mass General Brigham tested whether high-dose vitamin D3 taken after diagnosis affected COVID-19 outcomes, including the risk of developing long COVID. The study was conducted as a randomized clinical trial and included adults who had recently tested positive for COVID-19 plus some household members. The published report described a possible benefit for longer-term symptoms but found no effect on acute illness severity, hospital visits, or emergency care. Investigators noted limitations related to the remote design and the timing of supplementation and said larger trials are planned to follow up on these findings. Key findings: - The trial included 1,747 adults who recently tested positive for COVID-19 and 277 household members. - Participants were assigned to receive either vitamin D3 supplements or a placebo for four weeks. - Vitamin D supplementation did not significantly change short-term outcomes such as symptom severity, hospital visits, or emergency care. - There was no observed difference between groups in the likelihood that household contacts contracted the virus. - Among participants who closely followed the regimen, 21% of those taking vitamin D reported at least one ongoing symptom at eight weeks versus 25% in the placebo group, as reported in the study. - The researchers reported limitations, including remote conduct of the trial and that supplementation began several days after diagnosis; additional trials are planned. Summary: The trial produced a modest signal that vitamin D supplementation after diagnosis might be linked with fewer reported lingering symptoms at eight weeks, while showing no change in acute severity or household transmission. Researchers described the result as a promising indication that requires larger and earlier studies, and they are planning further trials to examine vitamin D for people already experiencing long COVID.