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Lower vitamin D levels associated with higher Covid-19 mortality rates, Anglia Ruskin University finds

An association has been found between lower levels of vitamin D and higher Covid-19 mortality rates.

The study, led by Dr Lee Smith of Anglia Ruskin University in Cambridge, and Petre Cristian Ilie, lead urologist of Queen Elizabeth Hospital King's Lynn NHS Foundation Trust, examined data across 20 European countries.

Dr Lee Smith, Anglia Ruskin University (34438059)
Dr Lee Smith, Anglia Ruskin University (34438059)

Vitamin D modulates the response of our white blood cells - a key component of our immune system - by preventing them from releasing too many inflammatory cytokines.

These are proteins we produce to fight an invading infection, but which also lead to the inflammatory symptoms we experience, such as fever.

SARS-CoV-2, the virus that causes Covid-19, is known to cause an excess of pro-inflammatory cytokines. The sickest patients suffer what is known as a ‘cytokine storm’ - a severe immune response to the infection that causes major inflammation.

Previous observational studies have shown an association between low levels of vitamin D and an individual’s susceptibility to acute respiratory tract infections.

Dr Lee Smith, reader in physical activity and public health at Anglia Ruskin University, said: “We found a significant crude relationship between average vitamin D levels and the number Covid-19 cases, and particularly Covid-19 mortality rates, per head of population across the 20 European countries.

“Vitamin D has been shown to protect against acute respiratory infections, and older adults, the group most deficient in vitamin D, are also the ones most seriously affected by Covid-19.

Total confirmed Covid-19 deaths per million across the world. Graphic: Our World in Data
Total confirmed Covid-19 deaths per million across the world. Graphic: Our World in Data

“A previous study found that 75 per cent of people in institutions, such as hospitals and care homes, were severely deficient in vitamin D. We suggest it would be advisable to perform dedicated studies looking at vitamin D levels in Covid-19 patients with different degrees of disease severity.”

Although it can be found in oily fish, we get most of our vitamin D from exposure to sunlight, so it might seem counter-intuitive that Scandinavian countries have experienced among the lowest per head mortality rates in Europe, while warmer, sunnier countries in southern Europe have been badly hit.

But the study shows Italy and Spain have lower average vitamin D levels than most northern European countries, partly because those in southern Europe - particularly the elderly - avoid the strong sun, and their darker skin pigmentation also reduces natural vitamin D synthesis.

Northern European countries have higher average levels of vitamin D, the study says, possibly because people living there avoid the sun less, but also due to a high consumption of cod liver oil and vitamin D supplements. In Finland, milk is also fortified with vitamin D.

Average levels of vitamin D are also lower among those over 70, due to decreased sun exposure and synthesis of vitamin D. The majority of Covid-19 deaths have been among the elderly.

But while the study finds an association between Vitamin D levels and Covid-19 mortality rates, it may tell the full story.

Petre Cristian Ilie, lead urologist of Queen Elizabeth Hospital King's Lynn NHS Foundation Trust, said: “Our study does have limitations however, not least because the number of cases in each country is affected by the number of tests performed, as well as the different measures taken by each country to prevent the spread of infection. Finally, and importantly, one must remember correlation does not necessarily mean causation.”

Note that country-by-country comparisons are also complicated by different testing regimes.

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