Does daily vitamin D supplementation prevent COVID-19? A hard look at the evidence.

Part 3 in the series on vitamin D.

The following post is strictly educational and is not intended as medical advice. Please consult your doctor before making any changes to your supplementation, diet, or lifestyle.

---

This is part 3 of my vitamin series. In the next part of this series, part 4, I will be discussing vitamin D and cancer. That is where things get really interesting, and for which I believe the vitamin D signal for health is the most compelling.

Subscribe for free to make sure you receive the update and don’t miss out.

---

Lots of hype from early in the pandemic suggested that vitamin D might have a dramatic impact on COVID-19 outcomes.

For example:

And this one, the likes of which would often be talked about by Joe Rogan and his guests:

This hype--and effect sizes especially of 2-3 fold reduction in risk--were never justified by good evidence.

But, some data from two meta-analyses of randomized controlled trials by Adrian Martineau did suggest a modest benefit (10%) to vitamin D for acute respiratory diseases.

Therefore, scientists conducted two large, rigorous, randomized controlled trials to address this question for COVID in particular: does vitamin D prevent the disease or make it better?

The first trial, in 6200 subjects in the UK, showed no benefit.

It is thought that vaccination may have masked the effect of vitamin D on COVID, plus many people in the control group also took vitamin D supplements.

There was some effect on COVID infection, but it wasn't significant.

Link.

Another study with 34601 participants found no effect. Some interpreters of this study have suggested that adequate levels of vitamin D (just 20mg/dL) in 86% of participants may explain this lack of effect; perhaps low levels are necessary for vitamin D to protect against COVID.

Overall, the randomized controlled trial literature showed no effect of vitamin D on COVID outcomes. It seems reasonable therefore to suggest that in those who have been vaccinated or have adequate vitamin D (just >20 mg/dL), vitamin D is unlikely to prevent COVID.

In other people, say, those who have not been vaccinated or with very low levels of vitamin D, supplemental vitamin D may help prevent COVID.

It's also possible that vitamin D specifically does not help with COVID, but only prevents other respiratory infections.

To summarize:

The current evidence is not yet clear on the point of COVID (i.e., there is no good evidence that vitamin D helps with COVID), and the evidence for acute respiratory infections is not definitive.

I personally take a low dose of vitamin D (1000 IU) because I think that it has little downside (for me), because I was severely deficient (9 ng/dL) when tested, and because I think the signal of potential benefits still are enough to justify taking a low dose.

Become a paid subscriber to receive a 20% off of vitamin D from Thorne: