Canadian researchers investigating a potential link between vitamin D and COVID-19 have found no evidence that the vitamin can protect individuals against either the incidence or the severity of the disease.
The new study, published in PLOS Medicine, marks the latest and most comprehensive blow to hopes that vitamin D supplements might help shield the public during the pandemic.
To assess the link between vitamin D and COVID-19, the researchers conducted a Mendelian randomisation study of genetic variants associated with increased vitamin D levels, including 4,134 individuals with COVID-19 and 1.2 million without it, across 11 countries.
The results showed no evidence for a causal relationship between higher vitamin D levels and reduced susceptibility to or severity of the disease. The authors recommend that future trials focus on more promising therapeutic treatments for COVID-19.
Mendelian randomisation is a method that uses measured variations in genes to estimate whether or not there is a causal relationship between a genetic factor and a disease. It’s particularly helpful at determining causation in the presence of other confounding factors, as in the case of COVID-19, where factors like age and comorbidity play a role in disease severity.
While the study provides compelling evidence, the authors note its limitations. Importantly, they did not investigate the relationship between vitamin D and COVID-19 in individuals who are vitamin D deficient, and do not rule out the possibility that supplements may affect the contraction and severity of COVID-19 among such patients. The genetic variants used were also only taken from European individuals, so further studies are required.
Vitamin D is a commonly touted supplement for preventing the common cold and influenza, but the science is not settled on its efficacy against those illnesses, either.
Amalyah Hart is a science journalist based in Melbourne.
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