In a growing list of studies on vitamin D and its link with COVID-19 disease, British researchers 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.
Previous observational studies have reported an association between low levels of vitamin D and susceptibility to acute respiratory tract infections.
"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," said study researcher Dr Lee Smith from Anglia Ruskin University in the UK.
According to the researchers, Vitamin D modulates the response of white blood cells, preventing them from releasing too many inflammatory cytokines. The COVID-19 virus is known to cause an excess of pro-inflammatory cytokines.
Italy and Spain have both experienced high COVID-19 mortality rates, and the new study, published in the journal Aging Clinical and Experimental Research, shows that both countries have lower average vitamin D levels than most northern European countries.
This is partly because people in southern Europe, particularly the elderly, avoid the 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.
Scandinavian nations are among the countries with the lowest number of COVID-19 cases and mortality rates per head of population in Europe.
"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," Smith said.
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," Smith added.
"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," said Petre Cristian Ilie, lead urologist of Queen Elizabeth Hospital King's Lynn NHS Foundation Trust.
Another study, published last month in the journal Nutrients, suggested that supplements containing vitamins C and D and other micronutrients are a safe, effective and low-cost means of helping your immune system fight off COVID-19 and other acute respiratory tract diseases.
