Vitamin D deficiency or more properly hypovitaminosis D is a group of related nutrition disorders characterized by softening of bones.

In children, the disease goes by the name of rickets.  Bones, particularly the long bones of the arms and legs grow more slowly and, when they fail to harden properly, they can become malformed by the loads placed upon them, particularly in the legs.  Symptoms usually first appear in the skull, which remains soft and does not properly fuse.

In adults, the disorder is described as osteomalacia.  In addition to brittle bones, the patient will also suffer from weakness of the muscles that attach to bones.

In the elderly, vitamin D deficiency is a major cause of osteoporosis.

Hypovitaminosis D at Wikipedia

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