Vitamin D Crucial To Activating Immune Defenses (Medical News Today) Scientists at the University of Copenhagen have discovered that Vitamin D is crucial to activating our immune defenses and that without sufficient intake of the vitamin, the killer cells of the immune system - T cells - will not be able to react to and fight off serious infections in the body. For T cells to detect and kill foreign pathogens such as clumps of bacteria or viruses, the cells must ... [News Source]