The vitamin D receptor (VDR) is a steroid hormone nuclear receptor, which means that it is located on the nucleus of a cell and is responsible for directly regulating the production of proteins from genetic code.

Because the biological effects of vitamin D are mediated through the vitamin D receptor, using VDR knockout mice, mice whose genes that code for the VDR have been inactivated, is one of the best ways for researchers to model vitamin D deficiency in humans. VDR knockout mice replicate many of the symptoms of human clinical vitamin D deficiency, including rickets, hypocalcemia, osteomalacia, and hyperparathyroidism.