The case is simple: we know vitamin D – the “sunshine vitamin” – is involved in immune function, so could it help us fight off the virus?
Some, such as the Labour MP Rupa Huq, are pretty certain of the answer. On [January 12] she wrote an article in the Evening Standard where she described vitamin D as “wonderstuff” that “offers us all hope to stamp out this dreaded disease”.
What does the evidence say on vitamin D and Covid-19? You might think that after nearly a year’s worth of studies, we’d have a pretty good idea of the answer. Far from it.
Much of the research is low-quality, with small samples and questionable analyses. More importantly, observational research is bedevilled by what epidemiologists call “confounding”. For example, if older people, or those with darker skin, are more at risk of vitamin D deficiency, and they’re more at risk of severe Covid-19 for other reasons, this kind of study might mistakenly link the deficiency and the disease – even if one doesn’t cause the other.
Promoting the idea that there’s a simple, dramatically effective solution – “wonderstuff”! – that boosts our immune system and prevents the disease could easily lull people into a false sense of security: “I’ve taken my vitamin D capsule, so maybe I can do without wearing a mask today.”