If there is one thing you can rely on in this pandemic, it is this: at least once a month a new article comes out in the media claiming that vitamin D helps prevent Covid-19.
The thing is simple: we know that vitamin D – the “sunshine vitamin” – is involved in immune function, so can it help us fight the virus?
Some, like Labor MP Rupa Huq, are quite sure of the answer. On Tuesday (January 12) she wrote an article in the Evening standard where she described vitamin D as a “panacea” that “offers us all hope to eradicate this dreaded disease.” She wrote that its benefits have been “hushed up” – perhaps, she suggested, because cheap vitamin pills can’t be monetized by Big Pharma and are less glamorous than a vaccine.
Huq’s article appeared a few days after the publication of one Observer piece describing how she and David Davis, the Conservative Member of Parliament, had become unlikely allies on this issue, campaigning to reduce what they consider to be the UK’s vitamin D deficiency. Huq and Davis are frustrated that agencies such as Public Health England say there is insufficient evidence to promote the vitamin, which Davis says could “potentially save tens of thousands of lives” during the pandemic.
Why To do the experts disagree with Huq and Davis? What Does the Evidence Say About Vitamin D and Covid-19? You might think that after nearly a year of studying, we would have a pretty good idea of the answer. Far from it.
Most of the Covid-19 / vitamin D research takes the form of observational studies – where researchers look at the correlation of vitamin D levels in the blood with the risk of getting Covid-19, or the severity of the sickness. In the meantime, there have been quite a few such studies and researchers have conducted meta-analyzes to pool all the data and draw broad conclusions.
If you dig through those meta-analyzes for a moment, things might look optimistic. a meta-analysis found that although vitamin D was not associated with the risk of getting Covid-19, it was more likely to be deficient in severe cases. Another found that depending on how you measure it, a higher vitamin D level is sometimes associated with a lower risk of infection and hospitalization. A third found lower vitamin D levels in Covid-19 patients compared to those without the disease.
[See also: Stuart Ritchie on the “three Cs” key to preventing the spread of coronavirus]
Exciting, right? Not really. Much of the research is of low quality, with small sample sizes and questionable analyzes. More importantly, observational research is hampered by what epidemiologists call “confounding.” For example, if older people, or those with dark skin, are more at risk for vitamin D deficiency, and they are more at risk for severe Covid-19 for other reasons, this type of research may falsely link the deficiency to the disease. – even if one does not cause the other.
What we need are randomized trials, where researchers give Covid-19 patients either vitamin D or a placebo and test if it’s vitamin ensures a better result. Surprisingly, only two exist so far. The first was a Spanish study that found Covid-19 patients who received some type of vitamin D supplement fared better. The above Observer article said this study “showed almost conclusively that low vitamin D levels play a critical role in causing increased death rates.” That’s dramatically far from reality: This was a pilot study with only 76 participants, and some clear defects in its design.
The second is a bit bigger study from Brazil, which found reasonably conclusive no benefits of vitamin D supplementation for severe Covid patients. It has not yet been published in a peer-reviewed journal, but strangely enough it is not mentioned by vitamin D advocates.
You may think: what’s the downside? Vitamin D is cheap. We all stay indoors during lockdown and therefore get less sunlight. Even if vitamin D doesn’t help fight Covid-19, is it still a good idea to take supplements? But this is one motte-and-bailey argument – where someone makes a very specific, controversial claim, that claim is attacked and they retreat to a much more general – but more defensible – point of view. We were not talking about the general benefits of vitamin D – we were talking about benefits for Covid-19. And the honest answer to this point is that science hasn’t given us any clarity: we just don’t know if it’s having an effect.
And there to be cons. There is a new, more transmittable variant of Covid-19, and we need people who are extremely careful not to catch it. Promote the idea that there is a simple, dramatically effective solution – “wonderstuff”! – that strengthens our immune system and prevents the disease from easily putting people in a false sense of security: “I took my vitamin D capsule, so maybe I can do it today without wearing a mask.”
A lot of more trials with Vitamin D and Covid-19 are underway, so we’ll get a more definitive answer shortly. Until then, let’s put aside the exaggerated claims about almost magical substances and sinister conspiracies. It may feel unsatisfying, but, as with so many parts of the coronavirus debate, the only sensible scientific view of vitamin D is one of uncertainty.
[See also: Stuart Ritchie on Covid-19 and the problem of anti-vaxxers]