Effects of single high-dose vitamin D3 on fracture healing. An ultrastructural study in healthy guinea pigs.

The benefits of vitamin D3 on fracture healing have been commonly demonstrated in vitamin-D3-depleted animal models. The aim of this study was to examine the effects of a single high dose of vitamin D3 on fracture healing in a healthy animal model, which has not been previously reported. Twenty healthy young adult guinea pigs were randomly divided into groups as 'control' and 'vitamin D', and their right tibias were fractured with digital manipulation. Guinea pigs in vitamin D group were injected intramuscularly with 50,000 i.u./kg of vitamin D3. The animals were killed at 7, 14, 21 and 28 days following fracture. Ultrastructural analysis of the harvested tibias revealed that a single high dose of vitamin D3 stimulated fracture healing. The observed effects at the fracture zone in a healthy animal model included advancement of blood supply, acceleration of synthesis and organization of collagen fibres, acceleration of the proliferation and differentiation of osteoprogenitor cells, and activation of the mineralization of the matrix.