The healthy range of vitamin D in the body is 20 to 50 nanograms per milliliter. A reading of 12 nanograms or less is a sign of a deficiency, notes WebMD.
Vitamin D is produced by being in the sunshine. It helps the body absorb calcium and keeps bones healthy. If a person has a very restricted diet or does not get in the sun often, they may have a vitamin deficiency. Dark-skinned people also have a harder time producing vitamin D. The disease most commonly associated with a lack of vitamin D is rickets, as noted on WebMD. This disease causes the bones to become weak and creates deformities. Having the correct amount of vitamin D also helps prevent diabetes.