If there’s one thing you can trust in this pandemic, it’s 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 is the “vitamin of the sun” involved in immune function, so could it help us fight the virus?
Some, like Labor MP Rupa Huq, are pretty sure of the answer. On Tuesday (January 12) he wrote an article in Standard in the evening where he described vitamin D as a “wonder” that “offers us all hope to eliminate this dreaded disease”. He wrote that his profits are “off”; perhaps, he suggested, because Big Pharma can’t make revenue with cheap vitamin pills and is less glamorous than a vaccine.
Huq’s article appeared a few days after the publication of a Observer a piece describing how she and David Davis, the Conservative MP, had become unlikely allies on the issue, campaigning to reduce what they consider vitamin D deficiency. Huq and Davis are frustrated because bodies like Public Health England say there is not enough evidence to promote the vitamin, which Davis says could “save tens of thousands of lives” during the pandemic.
Because do do experts disagree with Huq and Davis? What do the tests say about vitamin D and Covid-19? You might think that after almost a year of study, we would have a good idea of the answer. Far.
Most research on vitamin D / Covid-19 is conducted in the form of observational studies, where researchers analyze the correlation of vitamin D levels in the blood with the risk of obtaining Covid-19 or the severity of disease. So far, there have been quite a few such studies and researchers have done meta-analyzes to group all the data and try to draw broad conclusions.
If you only analyze these meta-analyzes, the case may seem optimistic. One 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 it is measured, a higher level of vitamin D is sometimes associated with a lower risk of infection and hospitalization. One-third found lower levels of vitamin D in patients with Covid-19 compared with those who did not have the disease.
[See also: Stuart Ritchie on the “three Cs” key to preventing the spread of coronavirus]
Exciting, isn’t it? Not really. Much of the research is of low quality, with small samples and questionable analyzes. More importantly, observational research is affected by what epidemiologists call “confusing”. For example, if older or darker-skinned people are at higher risk for vitamin D deficiency and are at higher risk for severe Covid-19 for other reasons, this type of study could erroneously link the deficiency to the disease – even all if one does not cause the other.
What we need are randomized trials, where researchers give patients Covid-19 vitamin D or a placebo and check if the vitamin causes a better result. Surprisingly, there are only two so far. The first was a Spanish study that found that Covid-19 patients with one type of vitamin D supplement tended to do better. The aforementioned Observer The article said that this study “was about to unequivocally demonstrate that low levels of vitamin D play a key role in causing an increase in mortality rates.” This is dramatically far from reality: it was a pilot study with only 76 participants, and some clear defects in its design.
The second is a little bigger study from Brazil, which convincingly found no benefit from vitamin D supplementation for severe Covid patients. It has not yet been published in a peer-reviewed journal, but curiously it is not mentioned by vitamin D advocates.
You might be thinking: what’s the downside? Vitamin D is cheap. We all stay indoors during closing and therefore receive less sunlight. Even if vitamin D doesn’t help fight Covid-19, surely it’s a good idea to take supplements anyway? But this is one motte and bailey argument: where someone makes a very specific and controversial statement, that statement is attacked and withdrawn to a much more general but more defensible position. We weren’t talking about the general Vitamin D Benefits: We talked about benefits for Covid-19. And the honest answer right now is that science hasn’t given us any clarity – we just don’t know if it has an effect.
And there they are disadvantages. There is a new, more transmissible variant of Covid-19 and we need people to be very careful not to catch it. Promoting the idea that there is a simple and effectively spectacular solution: “wonderstuff”. – which boosts our immune system and prevents the disease from easily calming people into a false sense of security: “I’ve taken my vitamin D capsule, so maybe I can do without wearing a mask today.”
Lots of there are more vitamin D and Covid-19 tests on the way, so we’ll get a more definitive answer soon. Until then, we dismiss the exaggerated claims about quasi-magical substances and sinister conspiracies. It may seem unsatisfactory, but, as with so many parts of the coronavirus debate, the only sensible scientific view of vitamin D is uncertainty.
[See also: Stuart Ritchie on Covid-19 and the problem of anti-vaxxers]