New international research involving Trinity College Dublin (TCD) has found further evidence that vitamin D may help to protect against severe Covid-related disease and death.

Researchers found that ambient ultraviolet B (UVB) radiation at an individual’s place of residence in the weeks before Covid-19 infection, was strongly protective against severe disease and death.

UVB radiation is key for vitamin D production in the skin.

Previous studies have linked vitamin D deficiency with an increased susceptibility to viral and bacterial respiratory infections. Furthermore, several observational studies have shown a strong correlation between vitamin D deficiency and Covid-19, however it could be that these effects are a result of other factors, such as obesity, older age or chronic illness, which are also linked with low vitamin D.

To overcome this, researchers were able to calculate a “genetically-predicted” vitamin D level that is not confounded by other demographic, health and lifestyle factors, by using the information from over 100 genes that determine vitamin D status.

The Mendelian Randomisation is a particular analytical approach that enabled researchers to investigate whether vitamin D and Covid-19 might be causally linked using genetic data. While a few earlier studies attempted this, they failed to show a causal link, but this could be because UVB radiation sunshine, which is the most important source of vitamin D for most people, was ignored.

For the first time, researchers looked jointly at genetically-predicted and UVB-predicted vitamin D levels. Almost half a million people in the UK took part in the study, and ambient UVB radiation before Covid-19 infection was individually assessed for each participant.

When comparing the two variables, researchers found that correlation with measured vitamin D concentration in the circulation was three-fold stronger for UVB-predicted vitamin D level, compared to genetically-predicted.

The researchers found that ambient UVB radiation at an individual’s place of residence preceding Covid infection was strongly and inversely associated with hospitalisation and death. They said that this suggests that vitamin D may protect against severe Covid-19 disease and death.

Additionally, while the results from the Mendelian Randomisation analysis were not conclusive, some indication of a potential causal effect was noted. Because of the relatively weak link between genetically-predicted vitamin D level that is used for Mendelian Randomisation analysis, it is possible that the number of cases in the current study was too small to convincingly determine causal effect. However, future larger studies may provide the answer.

“Our study adds further evidence that vitamin D might protect against severe Covid-19 infection. Conducting a properly designed Covid-19 randomised controlled trial of vitamin D supplementation is critical. Until then, given that vitamin D supplements are safe and cheap, it is definitely advisable to take supplements and protect against vitamin D deficiency, particularly with winter on the horizon,” commented one of the study’s senior researchers, Prof Lina Zgaga, of TCD.

This was echoed by another senior researcher, Prof Evropi Theodoratou, of the University of Edinburgh, who said that given the lack of highly effective therapies against Covid-19, “we think it is important to remain open-minded to emerging results from rigorously conducted studies of vitamin D”.

“Our study supports the recommendation of vitamin D supplementation for not only the maintenance of bone and muscle health during the lockdown, but also the potential benefits in relation to protection from Covid-19,” added researcher, Dr Xue Li of Zhejiang University in China.

The findings are published in the journal, Scientific Reports, and can be viewed here.