vitamin D really does protect against COVID-19 has been mixed.The vitamin is essential for maintaining healthy bones and muscles, but there is also good evidence that it provides some protection against contracting infections of the respiratory tract.So, in theory, it could protect against COVID-19, principally a respiratory infection.Another line of evidence in its favor is the observation that people susceptible to vitamin D deficiency — including those with obesity, older adults, and individuals of Black or Asian ethnic origin — are also vulnerable to COVID-19.An unpublished study found a link between mean levels of vitamin D in the populations of 20 European countries and the number of COVID-19 cases and mortality rates in the.