Scientists have found an association between low average levels of vitamin D, and high numbers of COVID-19 cases and mortality rates across 20 European countries, and call for dedicated studies to probe into the relationship.
Based on earlier studies, the researchers, including Lee Smith of Anglia Ruskin University in the UK, said there is an association between low levels of vitamin D and susceptibility to acute respiratory tract infections.
In the current research, they said vitamin D modulates the response of white blood cells, preventing them from releasing too many inflammatory molecules called cytokines which are produced in excess in patients with severe COVID-19.
Italy and Spain have both experienced high COVID-19 mortality rates, and according to the new study, both countries have lower average vitamin D levels than most northern European countries.
They said this is partly because people in southern Europe, particularly the elderly, avoid strong sun, while skin pigmentation also reduces natural vitamin D synthesis.
The highest average levels of vitamin D are found in northern Europe, due to the consumption of cod liver oil, and vitamin D supplements, and possibly less sun avoidance, the researchers said.
They said Scandinavian nations are among the countries with the lowest number of COVID-19 cases and mortality rates per head of population in Europe.
"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," Lee Smith, study co-author from Anglia Ruskin University, said.
The researchers said 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.
"A previous study found that 75 per cent of people in institutions, such as hospitals and care homes, were severely deficient in vitamin D," Smith said.
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," he added.
Citing the limitations of the study, the researchers said 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.
"Importantly, one must remember correlation does not necessarily mean causation," said study co-author Petre Cristian Ilie from Queen Elizabeth Hospital in the UK.
