Matt Ridley: Vitamin D and Covid-19

There has long been evidence that a sufficiency of vitamin D protects against viruses

A suggestive set of numbers was published online in April by a medical scientist in the Philippines, Dr Mark Alipio. Of 49 patients with mild symptoms of Covid-19 in three hospitals in southern Asian countries, only two had low levels of vitamin D; of 104 patients with critical or severe symptoms, only four did not have low levels of vitamin D. 

The more severe the symptoms, the more likely a patient was to be not just low but deficient in the vitamin. Could vitamin D deficiency make the difference between getting very ill or not?

There has long been evidence that a sufficiency of vitamin D protects against viruses, especially respiratory ones, including the common cold. Vitamin D increases the production of antiviral proteins and decreases cytokines, the immune molecules that can cause a “storm” of dangerous inflammation. 

It has long been suspected that most people’s low vitamin D levels in late winter partly explain the seasonal peaking of flu epidemics, and rising vitamin D levels in spring partly explain their sudden ending. Vitamin D is made by ultraviolet light falling on the skin, so many people in northern climates have a deficiency by the end of winter. Eating fish and eggs helps, but it is hard to get enough of it in the diet.

Here is a list of people who are more likely to be vitamin D deficient than the average: dark-skinned people (pigment blocks sunlight); obese people (the vitamin gets sequestered in fat cells); type-2 diabetics (vitamin D improves the body’s sensitivity to insulin); the elderly (they tend to avoid the sun and eat more frugally); city dwellers (they see less sunlight). Does that list ring any bells? All appear to be more likely to hospitalised with severe cases of Covid-19.

In addition, men tend to have slightly lower levels of vitamin D than women in winter, but slightly higher in summer, though the difference is probably not enough to explain why men are much more likely to die of Covid-19.

One recent study in Manchester found that average levels of vitamin D were 30 per cent higher in summer than in winter and three times as high at all times in white people as in South Asians. The latter had a median level of just 5.8 nanograms per millilitre in their blood in winter, way below the 20 that is regarded as sufficient. Surprisingly, despite guidelines from Public Health England, NHS GPs do not routinely check vitamin D levels or advise taking supplements.

Might it not be a good idea to tell everybody to take vitamin D supplements at this time, just in case it helps? In a letter to the British Medical Journal last week urging attention to Dr Alipio’s results, a long list of doctors wrote as follows: “Vitamin D biology is a mature well-researched field, dating back 100 years. Doses, and risks, within clinical parameters, are established and well quantified. Governmental intake guidance exists. Vitamin D deficiency is a medically accepted condition, requiring treatment.”

And for goodness sake, will somebody please tell the police to stop harassing sunbathers in parks?

Matt Ridley, a member of the British House of Lords, is an acclaimed author who blogs at www.rationaloptimist.com.