1 alpha, 25-Dihydroxyvitamin D3 a metabolite of vitamin D that promotes bone repair.

1 alpha, 25-dihydroxyvitamin D3, the hormonal form of vitamin D3 that mediates calcium translocation in intestine and bone, was tested for its ability to promote fracture repair. Chicks were raised on a vitamin D-deficient diet supplemented with 1 alpha, 25-dihydroxyvitamin D3 for 3 weeks. Following fracture of the humerus, those chicks that did not receive continued 1 alpha, 25-dihydroxyvitamin D3 supplementation showed prolonged fracture healing, abnormal enchondral bone formation delayed remodeling of woven bone and osseous union, but normal formation of callus. Fracture repair in chicks receiving 1 alpha, 25-dihydroxyvitamin D3 was normal. These data indicate that 1 alpha, 25-dihydroxyvitamin D3 promotes bone repair in the absence of vitamin D3, 25-hydroxyvitamin D3, and 24,25-dihydroxyvitamin D3.