A randomized trial tested whether vitamin D3 could help people with COVID-19 recover better or avoid severe outcomes.
The answer, at least for the acute phase, was no.
People who took vitamin D did not have fewer healthcare visits, hospitalizations, or deaths compared to those who took a placebo. In other words, vitamin D did not meaningfully change how sick people got in the short term.
But there was a signal—subtle, not statistically definitive, but interesting for Vitamin D3 and Long COVID:
Vitamin D may help reduce the risk of long COVID.
I chatted over email with one of the lead authors, Dr. JoAnn Manson (Chief of the Division of Preventive Medicine at Harvard Medical School) about the study.
She explained:
“A key takeaway is that vitamin D supplementation looks promising for reducing the risk of developing long COVID but does not appear to affect the severity of the acute infection. This is probably because vitamin D tamps down inflammation and prevents the longer-term complications of long COVID but not symptoms that are already underway.”
That distinction matters.
Vitamin D may not help once symptoms are in motion, but it could play a role in how the body handles longer-term inflammation and recovery.
She also noted that this pattern is not new:
“These findings are consistent with our earlier findings in VITAL that vitamin D lowers biomarkers of inflammation (such as CRP) and reduces the future risk of autoimmune disease but doesn’t affect symptoms that are already ongoing.”
Interestingly, the potential benefit for long COVID appeared even though participants only took vitamin D for four weeks. Dr. Manson commented:
“It was surprising to us to see a signal for benefit against long COVID, given that the treatment period lasted only 4 weeks.”
There are some important limitations to keep in mind.
The study had to be conducted remotely during the pandemic, and vitamin D supplementation didn’t begin immediately after diagnosis. Dr. Manson points out:
“A limitation of the trial is that it had to be conducted entirely remotely due to the pandemic and vitamin D couldn’t be started until a few days after the COVID diagnosis. Ideally, we would have wanted to initiate vitamin D prior to, or immediately after, the COVID diagnosis, but this wasn’t feasible.”
So timing may matter.
And looking ahead, her recommendation is less about treating COVID after the fact, and more about baseline health:
“A recommendation would be to increase background intake of vitamin D during the winter or other periods when COVID and other viral infections become more prevalent. This may also reduce the risk of developing long COVID. We are planning an additional randomized trial to test high-dose vitamin D for treating the symptoms of long COVID.”
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More fun stuff to check out in the blog:
Are you spending too long on the toilet? Find out here.
How much does obesity increase your infectious disease risk? Check it out.
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