You might have missed it, but last week the UK Health Secretary Matt Hancock said that his government was recommending vitamin D supplements as a protective measure against the coronavirus.

But most of the attention focused on Mr Hancock’s stumbling around on the issue. One moment he dismissed vitamin D’s usefulness, saying there was no good evidence as to its efficacy.

The next he was touting it as a must-take prophylactic because the evidence was pretty good, after all.

There’s certainly been a fair bit of faffing about on the issue.

So what is the evidence?

A letter published three weeks ago in the British Medical Journal from an Australian doctor tells the story; more than 30 studies have demonstrated “that having optimal blood levels of (vitamin D) reduces COVID-19 risks: reduced risk of infection; reduced risk of severe disease; reduced risk of dying”.

The doctor, Peter J Lewis, a NSW GP with a special interest in integrative medicine, noted that “Many researchers now regard the evidence as overwhelming”.

“Despite this, there still will be those who say that we need ‘more research’, but in the meantime, there is little to be lost … and a huge amount to gain by recommending a decent daily dose of vitamin D3” for children and adults.

A comment piece published in Lancet in August made the same point – while laying out the long history of vitamin D’s perceived potential as a treatment for respiratory illness. It goes back nearly 90 years.

New evidence from Spain

In a study based at the Hospital Universitario Marqués de Valdecilla, 216 COVID-19 patients had their vitamin D levels measured. More than 80 per cent were found to have a vitamin D deficiency.

On average, men had lower vitamin D levels than women.

OK, one might argue, in the age of sunlight-phobia, that plenty of people are vitamin D deficient. Where’s the comparison with the broader population?

There wasn’t one … but, the doctors found that the patients with lower vitamin D levels also had raised serum levels of inflammatory markers such as ferritin and D-dimer.

Inflammation being the destructive hallmark of COVID-19, manifesting itself from the tip of the toes, to the lining of the blood vessels, the lungs and deep inside the brain.

Study co-author Dr José L. Hernández, of the University of Cantabria, observed: “Vitamin D is a hormone the kidneys produce that controls blood calcium concentration and impacts the immune system.

“Vitamin D deficiency has been linked to a variety of health concerns, although research is still under way into why the hormone impacts other systems of the body. Many studies point to the beneficial effect of vitamin D on the immune system, especially regarding protection against infections.”

He concludes: “Vitamin D treatment should be recommended in COVID-19 patients with low levels of vitamin D circulating in the blood since this approach might have beneficial effects in both the musculoskeletal and the immune system.”

He notes that supplements are especially important for “high-risk individuals such as the elderly, patients with comorbidities, and nursing home residents, who are the main target population for the COVID-19.”

For a technical explanation as to why vitamin D might work against COVID-19, see here.