PTH and hypercalcemia disease: Opposite to vitamin D receptor activator (VDRA), nutritional vitamin D compounds are unlikely to induce hypercalcemia using a normal regimen because its 1α-hydroxylase activation is regulated by PTH, FGF-23 and 24-hydroxylase.Therefore, a serum 25(OH)D level up to 100 ng/mL is considered safe [1].