Vitamin D in hypoparathyroidism: insight into pathophysiology and perspectives in clinical practice.

Hypoparathyroidism (HypoPT) is a rare endocrine disorder characterized by the absence or insufficient parathyroid hormone production resulting in chronic hypocalcemia. Complications of HypoPT include perturbation of several target organs. The conventional treatment consists of the administration of active vitamin D, namely calcitriol. Regarding vitamin D status, few data are available, mostly in HypoPT subjects supplemented with parent vitamin D. In addition, perturbation of vitamin D metabolism has been poorly investigated, as well as the contribution of altered vitamin D status on the clinical expression of the disease. The most recent consensus on the management of chronic HypoPT suggests the baseline evaluation of serum 25-hydroxy-vitamin D [25(OH)D] and supplementation with parent vitamin D with the aim to achieve and maintain serum 25(OH)D levels in the range of 30-50 ng/mL. The rationale for using supplementation with parent vitamin D (either ergocalciferol or cholecalciferol) in HypoPT would be to provide sufficient 25(OH)D substrate to the residual 1-α-hydroxylase activity, thus ensuring its conversion to active vitamin D in renal and extra-renal tissues. More data from experimental and clinical studies are needed for better assessing how these mechanisms may significantly influence metabolic control in HypoPT and eventually skeletal and extra-skeletal manifestation of the disease. Finally, future data will clarify how the currently available parent vitamin D compounds (ergocalciferol, cholecalciferol, calcifediol) would perform in addressing these specific issues.