A new study has found an association between low average levels of vitamin D and high numbers of COVID-19 cases and mortality rates across 20 European countries.
The research was led by researchers from Anglia Ruskin University and Queen Elizabeth Hospital King's Lynn NHS Foundation Trust.
Vitamin D and immune function
Previous observational studies have reported an association between low levels of vitamin D and susceptibility to acute respiratory tract infections. Vitamin D has also 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.
Vitamin D plays a role in immune function by modulating the response of white blood cells, preventing them from releasing too many inflammatory proteins. The COVID-19 virus is known to cause an excess of pro-inflammatory cytokines.
Links between vitamin D levels and COVID-19 cases, mortality
Italy and Spain have both experienced high COVID-19 mortality rates, and this new research found that both countries have lower average vitamin D blood levels than most northern European countries. This is partly because people in southern Europe, particularly the elderly, avoid strong sun, while skin darker coloured 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.
A previous study found that 75% of people in institutions, such as hospitals and care homes, were severely deficient in vitamin D.
The researchers suggest it would be advisable to perform dedicated studies looking at vitamin D levels in COVID-19 patients with different degrees of disease severity.
This study does have limitations.
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.
And importantly, this study was observational in nature and, as such, it does not prove that low vitamin D directly increases risk of COVID-19 infection or that higher blood levels are protective.
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