Uses: Vitamin D is used to treat and prevent bone disorders caused by low levels of vitamin D in the body (e.g., rickets, osteomalacia). It is also used with other medications to treat low levels of calcium or phosphate caused by certain disorders (e.g., hypoparathyroidism, pseudohypoparathyroidism, familial hypophosphatemia). Vitamin D helps your body absorb calcium and phosphorus. Having the right amounts of vitamin D, calcium, and phosphorus is important for building and keeping strong bones.