We provide a brief review of the significance of platelets, mitochondria, vitamin
D, serotonin, and the gut microbiome in COVID-19. We hypothesize that hyperactive
platelets and mitochondrial dysfunction, as well as low vitamin D level, gut dysbiosis,
and increased serum serotonin produced by enterochromaffin cells, may all represent
important aspects in the pathophysiology of COVID-19.