June 4 (UPI) -- There is no genetic evidence that vitamin D reduces the risk of contracting COVID-19, despite previous research suggesting the vitamin works as a protective measure against it, according to a study published this week in PLOS Medicine.
Vitamin D plays a role in having a healthy immune system. Research early in the pandemic suggested that lower levels of the nutrient could increase susceptibility to COVID-19, leading some to test whether increased levels of the vitamin would prevent getting the coronavirus.
Researchers at McGill University in Canada assessed the relationship between vitamin D levels and COVID-19 susceptibility and severity based on genetic comparisons between more than 14,000 people who had the disease and 1.2 million people from 11 countries who did not.
They found that among people who contract the virus, there was no difference between vitamin D levels and a likelihood of being hospitalized or falling ill.
The researchers say there is not enough evidence that vitamin D supplements can prevent or treat the disease.
"Most vitamin D studies are very difficult to interpret since they cannot adjust for the known risk factors for severe COVID-19 such as older age or having chronic diseases, which are also predictors of low vitamin D," study co-author Guillaume Butler-Laporte, a physician and researcher at McGill, said Friday in a press release.
By using a Mendelian randomization, the researchers say they were able to provide a clearer picture of the relationship between vitamin D and COVID-19 by better considering known risk factors for the disease.
But researchers also noted the study has limitations, such as not accounting for truly vitamin D deficient patients and using genetic variants only from European ancestry.
Further studies are needed to explore the relationship with vitamin D and COVID-19 outcomes in other populations, they said.
"Vitamin D supplementation as a public health measure to improve outcomes is not supported by this study," the researchers wrote in the study.
"Most importantly, our results suggest that investment in other therapeutic or preventative avenues should be prioritized for COVID-19 randomized clinical trials," they wrote.