Preliminary observations have correlated vitamin D levels and outcomes in COVID-19, allowing hypotheses on vitamin D as being protective from COVID-19 due to its potential benefits antiviral activity [155–167], attenuation of lung injuries [168–173], and possible slight suppressive although inconsistent effects on RAAS [174–177], and neutral effects on TMPRSS2 [178, 179], being a potential candidate to protect from SARS-CoV-2 infectivity, i.e., during its early stage, although only observational studies have been published to date. Here, TMPRSS2 is linked to COVID-19.