Vitamin D promotes kidney calcium reabsorption and regulates calcium and phosphate metabolism, as well as the intestinal absorption of calcium and phosphorus and bone mineralization events. Vitamin D is also known for its immunomodulatory properties. It has been shown in the literature that the active form of vitamin D, 1,25-dihydroxyvitamin D, performs multiple functions in the adaptive and innate immune system, as well as acting on the endothelial membrane. Recent evidence shows that vitamin D is a negative endocrine modulator of the renin–angiotensin system (RAS), with protection from diseases leading to lung damage, such as pneumonia caused by various pathogens. Vitamin D support associated with the use of antibiotics could be crucial to counteract these infectious diseases.