calcium-deficiency disorders
conditions caused by insufficient levels of calcium in the tissues. Absorption of calcium from food and its deposition in bone is facilitated by vitamin D, and deficiency of this vitamin is the usual cause of rickets, a disease of childhood marked by deformed bones and teeth and lax muscles, and osteomalacia, the adult form of rickets. Osteoporosis, in which the bones become brittle and break easily, is caused by resorption (loss) of calcified bone due to disease or aging (it is common in postmenopausal women). Tetany (muscle spasms) is due to a deficiency of calcium in the blood.