New research from Trinity College Dublin and University of Edinburgh has examined the association between vitamin D and COVID-19, and found that ambient ultraviolet B (UVB) radiation (which is key for vitamin D production in the skin) at an individual’s place of residence in the weeks before COVID-19 infection, was strongly protective against severe disease and death. The paper has been published in the journal Scientific Reports.
Previous studies have linked vitamin D deficiency with increased susceptibility to viral and bacterial respiratory infections. Similarly, several observational studies found a strong correlation between vitamin D deficiency and COVID-19, but it could be that these effects are confounded and in fact 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 “genetically-predicted” vitamin D levels, which are not confounded by other demographic, health, and lifestyle factors, by using the information from over one hundred genes that determine vitamin D status.
Mendelian Randomization is a particular analytical approach that enabled researchers to investigate whether vitamin D and COVID-19 might be causally linked using genetic data. Few earlier studies attempted this but failed to show a causal link. This could be because UVB radiation from sunshine which is the most important source of vitamin D for the majority of people was ignored.
Researchers, for the first time, looked jointly at genetically predicted and UVB-predicted vitamin D levels. Almost half a million individuals 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.
Researchers found that ambient UVB radiation at an individual’s place of residence preceding COVID-19 infection was strongly and inversely associated with hospitalization and death. This suggests that vitamin D may protect against severe COVID-19 disease and death. Additionally, while the results from the Mendelian Randomization analysis weren’t conclusive, some indication of a potential causal effect was noted. Because of the relatively weak link between genetically predicted vitamin D levels that are used for Mendelian Randomization analysis, it is possible that the number of cases in the current study was too small to convincingly determine causal effect, but future larger studies might provide the answer.
Materials provided by Trinity College Dublin. Content may be edited for clarity, style, and length.