An x-ray of the hand of a child with rickets, a childhood disorder involving softening and weakening of the bones. It is primarily caused by lack of vitamin D, calcium, or phosphate. Vitamin D may be absorbed from food by the intestines or may be produced by the skin when the skin is exposed to sunlight. In its active form, vitamin D acts as a hormone to regulate calcium absorption from the intestine and to regulate levels of calcium and phosphate in the bones. When the body is deficient in vitamin D, it is unable to properly regulate calcium and phosphate levels. If the blood levels of these minerals become too low, other body hormones may stimulate release of calcium and phosphate from the bones to the bloodstream to elevate the blood levels.
