Before you rush to the store and start hoarding Vitamin D supplements like they were toilet paper, let’s “D”-construct the currently available evidence. As I’ve described previously for Forbes, since your immune system is not used to seeing the SARS-CoV2, your body’s defenses can act like someone experiencing something like sex for the first time. Back in 2017, the BMJ published a systematic review and meta-analysis of randomized, placebo controlled clinical trials that evaluated how Vitamin D supplementation may affect the risk of getting acute respiratory tract infections. Additionally, while this systematic review suggested that Vitamin D supplementation could be associated with a lower risk of respiratory tract infections, it still did not prove that it can prevent such infections. Keep in mind that posting a manuscript on MedRxiv doesn’t mean that the manuscript has undergone peer-review or will ever make it to an respected scientific journal. On top of all that, a study published in the journal Diabetes and Metabolic Syndrome found no correlation between Vitamin D levels and Covid-19 infection risk among 348,598 people in the U.K. All told, right now, the grade for the amount of scientific evidence linking Vitamin D levels and Covid-19 risk would be not much better than a D. It hasn’t completely failed, but it’s not ready for a pass either. Moreover, even if it were to have some positive impact, Vitamin D certainly won’t do what social distancing, good hand hygiene, and properly disinfecting objects will do to prevent infection.