For months now there's been levels of research interest around vitamin D levels and developing covid-19, but this pre-print, association research paper, has an interesting note about bats and vitamin D - at least I thought it was!
"There is also an enigma: how comes, given the proven capacity of this coronavirus to mutate and spread at a very high rate among humans, that humans and other mammals were apparently relatively spared from coronaviruses until the current pandemics. How is it that among all mammals, bats are the principal reservoir of hundreds of coronaviruses strains? Interestingly, bats live mostly in the dark, and their vitamin D levels are so low that they are often undetectable. Bats have developed alternative pathways to regulate bone mineralization, but the lack of vitamin D associated with living in the darkness, might impair bats from eliminating these viruses, and this may explain why so many coronaviruses are present in bats."
https://www.medrxiv.org/content/10.1101/2020.09.04.20188268v1