Vitamin D3 is a more potent and bioavailable form compared to D2. Assists the body with calcium absorption. Vitamin D plays a regulatory role in the growth, differentiation, and proliferation of different types of white blood cells.8** It is important to regulate these processes to maintain immune balance. The T and B cells of the adaptive immune system are both regulated by vitamin D.** Many cells of the innate immune response also require vitamin D such as monocytes which need it to mature properly.** Adequate concentrations of vitamin D are also necessary for the synthesis of important proteins with immune-fighting properties. As we age, the skin produces vitamin D less efficiently.