Vitamin D supplements were hailed by many as the great hope for fighting Covid and people bought them in huge numbers.

But it turns out that, when it comes to fighting off the pandemic, they do absolutely nothing.

Taking vitamin D supplements does not cut the risk of catching Covid or reduce the severity of the symptoms if you do, according to the first major study into their effect on the virus.

Nor does it reduce the risk of developing long Covid.

Furthermore, the supplements don’t protect against other acute respiratory infections, such as the common cold, sinustitis, ear infections and laryngitis, either according to a nationwide study of 6,200 people, led by Queen Mary University of London.

“We were surprised and disappointed by the outcome given the work we’d done previously showing vitamin D protecting against other respiratory infections. But it is what it is,” Professor Adrian Martineau, an academic at Queen Mary University of London and respiratory specialist at the Barts Health NHS Trust, who is co-heading the trial, told i.

“If we had known whether it works we wouldn’t have done the trial, so there was a genuine question there and it was well worth doing,” he said.

“It was a big trial and we used a generous dose of vitamin D. We showed that people took it and their levels went up. And the trial was done at such a time when only a tiny number of people were vaccinated initially so we captured enough to see the effect if there was one,” he said.

But while the case for vitamin D as a defender against Covid may have waned, there remain many good health reasons for consuming the vitamin – which due to a quirk of mislabelling, isn’t really a vitamin at all, but a hormone.

The government currently recommends 10 micrograms a day, or 400 international units, to protect muscle and bone health. 

“The government advice on vitamin D isn’t based on any effects on respiratory infection it’s based on proven benefits for bone health and muscle health and those aren’t change by the results of this study,” Professor Martineau said.

Vitamin D is found in foods such as oily fish, red meat, egg yolks and liver but in much smaller quantities than the immune system needs to function properly.

The main source is sunlight so in the winter vitamin D levels drop considerably and supplements are advised.

People who are at highest risk of vitamin D deficiency include those who are older, or in institutions, or overweight, who often go outside less.

They also include people of colour as darker skin doesn’t absorb so much ultraviolet light and so produces less vitamin D.

Announcing the trial in October 2020, Professor Martineau told i: “There is genuine uncertainty here and the only way to resolve that is by doing the sort of trial that we propose.”

“There is quite a lot of suggestive evidence. There’s a bit of evidence from the lab and there’s the very, very striking observation that the people who tend to get the most severe disease look exactly like the people who are at highest risk of vitamin D deficiency,” he said.

The study is published on the medrxiv website as a ‘pre-print’ ahead of peer review for publication in a journal due to its timely nature.

The trial is much more indepth than previous studies looking into the effect of vitamin D supplements on preventing Covid because it was ‘randomised’.

This means large numbers of participants are randomly assigned to one of two groups; the experimental group, receiving the treatment that is being tested, and a comparison group or control, which isn’t.

By dividing them in this way, other potential factors that may also influence the outcome – such as health issues that may make a person more vulnerable to Covid – can be offset, or ironed out.

This means there is a much greater chance that a direct cause and effect – or lack of one – can be established than with ‘observational’ studies, which identify a link but can’t confirm the underlying cause.

The randomised trial was led by Queen Mary of London and also involved the Universities of Edinburgh and Swansea and Queens University Belfast.

By Percy