If there is anything you can trust in this pandemic, it is this: at least once a month, there will be a new article in the media arguing that vitamin D helps prevent Covid-19.
The case is simple: we know that vitamin D – the “sun vitamin” – is involved in immune function, so could it help us fight the virus?
Some, like Labor MP Rupa Huq, are sure of the answer. On Tuesday (January 12) she wrote an article in Evening Standard where she described vitamin D as a “wonder” that “offers us all hope to eradicate this dreaded disease”. She wrote that its benefits are “muffled” – perhaps, she suggested, because cheap vitamin pills cannot be monetized by Big Pharma and are less glamorous than a vaccine.
Huq’s article appeared a few days after the publication of a Observer an article that described how she and David Davis, the Conservative MP, became unlikely allies on this topic, campaigning to reduce what they see as the UK’s vitamin D deficiency. Huq and Davis are frustrated that bodies like Public Health England say there is not enough evidence to promote the vitamin, which Davis says “could potentially save tens of thousands of lives” during the pandemic.
Because Does do the experts disagree with Huq and Davis? What does the evidence say about vitamin D and Covid-19? You might think that after almost a year of studying, we would have a good idea of the answer. Far from it.
Most of the Covid-19 / vitamin D research is in the form of observational studies – where researchers examine the correlation of blood vitamin D levels with the risk of contracting Covid-19 or the severity of the disease. So far, there are some such studies, and the researchers have done meta-analyzes to gather all the data and try to draw broad conclusions.
If you just take a look at these meta-analyzes, the case may seem optimistic. 1 the meta-analysis found that although vitamin D was not associated with the risk of contracting Covid-19, severe cases were more likely to involve a deficiency. Another found that, depending on how you measure it, a higher level of vitamin D is sometimes associated with a lower risk of infection and hospitalization. A third found lower levels of vitamin D in patients with Covid-19 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 low quality, with small samples and questionable analyzes. More importantly, observational research is plagued by what epidemiologists call “confusion”. For example, if older people or those with darker skin have a higher risk of vitamin D deficiency and a higher risk of severe Covid-19 for other reasons, this type of study may erroneously link deficiency and disease – even if one does not cause the other.
What we need are randomized trials, where researchers give Covid-19 patients vitamin D or a placebo and test whether the vitamin causes a better result. Surprisingly, only two exist to date. The first was a Spanish study that found that patients with Covid-19 who received a type of vitamin D supplement tended to do better. The aforementioned Observer The article said that this study “came close to proving beyond doubt that low levels of vitamin D play a central role in increasing mortality rates.” This is dramatically far from reality: this was a pilot study with only 76 participants, and some clear flaws in your design.
The second is slightly larger study from Brazil, which convincingly found no benefits of vitamin D supplementation for critically ill patients with Covid. It hasn’t been published in a peer-reviewed journal yet, but strangely it hasn’t been mentioned by vitamin D advocates.
You may be thinking: what’s the downside? Vitamin D is cheap. We all stayed indoors during the block and therefore received less sunlight. Even if vitamin D does not help fight Covid-19, is it certainly a good idea to take supplements anyway? But this is a motte-and-bailey argument – where someone makes a very specific and controversial statement, that statement is attacked and they retreat to a much more general position – but more defensible. We were not talking about the general benefits of vitamin D – we were talking about the benefits of Covid-19. And the honest answer on this point is that science has failed to give us clarity: we just don’t know if it has any effect.
She it is disadvantages. There is a new and more communicable variant of Covid-19, and we need people to be very careful not to contract it. Promote the idea that there is a simple and dramatically effective solution – “wonders”! – which boosts our immune system and prevents disease could easily soothe people with a false sense of security: “I took my vitamin D capsule, so maybe I can go without a mask today.”
Many more vitamin D and Covid-19 tests are on the way, so we will have a more definitive answer soon. Until then, let’s put aside the exaggerated claims about quasi-magical substances and sinister conspiracies. It may seem unsatisfactory, but, as with many parts of the coronavirus debate, the only sensible scientific view of vitamin D is that of uncertainty.
[See also: Stuart Ritchie on Covid-19 and the problem of anti-vaxxers]