Helps to support the maintenance of bone density. Helps protect against osteoporosis Maintenance of blood calcium levels within a narrow range is vital for normal functioning of the nervous system as well as for bone growth and maintenance of bone density There is plenty of scientific evidence that vitamin D has several different effects on immune system function that may enhance your immunity and inhibit the development of autoimmunity.The active form of vitamin D inhibits proliferation and stimulates the differentiation of cells.