If there is one thing you can rely on in this pandemic, it is: there will be a new article in the media at least once a month arguing that vitamin D helps prevent Covid-19.
The point is simple: we know vitamin D – the “sunshine vitamin” – is involved in immune function, can it then help us fight the virus?
Some, like Labor MP Rupa Huq, are pretty sure of the answer. On Tuesday (January 12) she wrote an article in the Evening standard where she described vitamin D as a ‘miracle’ that ‘offers us all hope of eradicating this dreaded disease’. She wrote that its benefits were ‘reduced’ – perhaps, she suggested, because cheap vitamin pills could not be earned by Big Pharma, and that they were less glamorous than a vaccine.
Huq’s article appeared a few days after the publication of a Observer piece that described how she and David Davis, the Conservative MP, became unlikely allies on this issue and are campaigning for the reduction of what they see as vitamin D deficiency in the UK. Huq and Davis are frustrated because bodies like Public Health England say there is insufficient evidence to promote the vitamin, which Davis says could ‘save tens of thousands of lives’ during the pandemic.
Why do the experts disagree with Huq and Davis? What does the evidence say about vitamin D and Covid-19? You would think that after a year of study 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 look at the correlation of vitamin D levels in blood with the risk of getting Covid-19, or the severity of the disease. By this time, there were quite a few such studies, and researchers were doing meta-analyzes to put all the data together and draw broad conclusions.
If you just skip the meta-analyzes, the case may seem optimistic. One Meta-analysis found that although vitamin D is not associated with the risk of getting Covid-19, more severe cases have a deficiency. 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 levels of vitamin D 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 low quality, with small samples and questionable analyzes. More importantly, observational research is being tarnished by what epidemiologists call “confusing.” If older people, or those with darker skin, are more at risk of having vitamin D deficiency, and they are at risk of having severe Covid-19 for other reasons, this type of study may incorrectly address the deficiency and the disease. connected – even if the 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 outcome. Surprisingly, there are only two so far. The first was a Spanish study that found that Covid-19 patients who were given a type of vitamin D supplement tended to perform better. The aforementioned Observer According to this article, it is unequivocal to prove that low vitamin D levels play an important role in increased mortality rates. This is dramatically far from reality: it was a pilot study with only 76 participants, and some clearly defects in its design.
The second is a little bigger study from Brazil, which found quite convincingly no benefits of vitamin D supplementation for severe Covid patients. It is not yet published in a journal, but strangely enough it is not mentioned by the vitamin D proponents.
You may be thinking: what is the disadvantage? Vitamin D is cheap. We all stay indoors during lock-in and therefore get less sunlight. Even if vitamin D does not help combat Covid-19, is it still a good idea to take supplements? But it’s a motte-and-bailey argument – where someone makes a very specific, controversial claim, the claim is attacked and pulls them back to a much more general – but more defensible – position. We do not have about the general Benefits of Vitamin D – We talked about benefits of Covid-19. And the honest answer at this point is that science has not given us clarity: we simply do not know if it has an effect.
And there is disadvantages. There’s a new, more portable variant of Covid-19, and we need people to take the utmost warning not to catch it. To promote the idea that there is a simple, dramatically effective solution – ‘wonderstuff’! – which strengthens our immune system and prevents the disease from easily leaving people in a false sense of security: ‘I took my vitamin D capsule, so maybe I can do it without wearing a mask today.’
Very more trials with vitamin D and Covid-19 are on the way, so we will get a more definitive answer soon. Until then, let us make the exaggerated claims about quasi-magical substances and sinister conspiracies. This may feel unsatisfactory, but as with so many parts of the coronavirus debate, the only sensible scientific view on vitamin D is uncertainty.
[See also: Stuart Ritchie on Covid-19 and the problem of anti-vaxxers]