What is the pathophysiology of vitamin D deficiency?

Updated: Dec 15, 2020
  • Author: Vin Tangpricha, MD, PhD; Chief Editor: Romesh Khardori, MD, PhD, FACP  more...
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Inadequate circulating 25(OH)D is associated with elevated parathyroid hormone (PTH); this condition is called secondary hyperparathyroidism. The rise in PTH may result in increased mobilization of calcium from the bone, which leads to decreased mineralization of the bone.

Of note, prolonged exposure to the sun does not cause vitamin D toxicity. This is because after prolonged UVB radiation exposure, the vitamin D made in the skin is further degraded to the inactive vitamin D metabolites tachysterol and lumisterol.

As strongly suggested by genetic, molecular, cellular, and animal studies, extraskeletal effects related to vitamin D signaling include roles in cell proliferation, immune and muscle function, skin differentiation, and reproduction, with vitamin D having vascular and metabolic actions as well. Observational studies have pointed to a relationship between poor vitamin D status and almost all diseases connected to these extraskeletal influences. However, while randomized, controlled trials and Mendelian randomization studies have indicated that vitamin D supplementation can lower the incidence of some disorders, only mixed conclusions on the matter have been reached globally. [15]

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