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Vitamin D and Covid-19: An Update
Why vitamin D probably still can’t cure Covid-19
There are many scientific questions that have come up during the pandemic. We’ve investigated the efficacy of hydroxychloroquine, looked into school closures, and even checked to see whether spectacles could protect you from getting Covid-19 (the jury is still out on that one).
But perhaps the most consistent question that has been asked, over and over again, is whether vitamin D supplements can treat coronavirus effectively. The allure is understandable — vitamin D is cheap, relatively safe, and there’s some evidence that it can help with the common cold, which is often caused by coronaviruses similar to SARS-CoV-2. If it worked, it could make an enormous difference in the lives of people with Covid-19 and at a very low cost. Sadly, this has inspired endless shoddy studies that have meant that the question of whether vitamin D works for Covid-19 wasn’t answered very well (or at all) the last time I wrote about it in October 2020.
This makes the recent headlines all the more understandable. A study was put up on SSRN — a preprint server run by The Lancet — a few weeks ago that purported to show a 60% decrease in mortality for people with Covid-19 who were given calcifediol (a metabolite of vitamin D) compared to a control group given treatment as usual. With such impressive-sounding results, the study soon went viral on Twitter and has been reported in news outlets around the world. If supplements really could prevent 60% of Covid-19 deaths, it would be a research finding that could literally change the course of the pandemic.
Unfortunately, as with most of the previous research, the evidence is much shakier than you might expect given the glowing headlines. Even more than a year into all of this, we still don’t really know if vitamin D does anything for Covid-19 at all.
The science
On first reading, the study itself is pretty simple. The authors apparently randomized people to receive either calcifediol or no treatment and followed them up until they either went to ICU, died, or were…
