In mouse models, the rickets, osteomalacia, muscle weakness, and secondary hyperparathyroidism observed in mice with global knockout of the VDR is largely, if not entirely57, reversed by feeding the mice a rescue diet of increased calcium and phosphorus, together with high lactose, which appears to facilitate calcium absorption58, or by engineering VDR expression just in the intestine59. Here, VDR is linked to secondary hyperparathyroidism.