Vitamin D assists intestinal absorption of calcium, phosphorus, and to a minor degree, magnesium. While taking higher amounts of Vitamin D may protect from several types of cancer or be helpful for some neurodegenerative conditions such as multiple sclerosis, excessive long-term intake of Vitamin D can result in above-normal serum calcium levels, and calcification of arteries and other soft tissue. Supplementing large amounts of Vitamin D and not increasing one's calcium intake at the same time will risk a high Vitamin D-induced calcium loss from bone as a result of insufficient intestinal calcium being available for absorption. This only applies to a very high oral intake of Vitamin D, but not to higher amounts acquired from sun UVB exposure... Full Text