Influence of vitamin D status and mechanical loading on the morphometric and mechanical properties of the mouse tibia

It is well known that vitamin D and mechanical loading play important roles in bone growth and development. However, the combined effect of the maternal vitamin D status and mechanical loading on the bone quality of growing and mature bones is still unclear. The aim of this study was to investigate the influence of the antenatal vitamin D status and mechanical loading on bone morphometric and mechanical properties in juvenile and adult bones. C57BL/6J mice were used to generate vitamin D-replete and vitamin D-depleted dams. The left tibiae of 8-week-old and 16-week-old offspring were mechanically loaded in vivo for two weeks. Both tibiae were dissected and scanned using a μCT imaging system. It was found that in the bones of 10-week-old juvenile offspring, the antenatal vitamin D-replete group significantly increased trabecular bone volume fraction (Tb.BV/TV), trabecular thickness (Tb.Th), cortical thickness (Ct.Th), bone stiffness and failure load; significantly decreased trabecular separation (Tb.Sp) and cortical marrow area (Ct.MA) only in loaded tibiae; and markedly increased Tb.Sp and Ct.MA only in non-loaded tibiae. In the bones of the 18-week-old adult offspring, the antenatal vitamin D status had a minimal effect on the bone morphometric and mechanical parameters. These data imply that antenatal vitamin D repletion results in increased responses to mechanical loading only in the juvenile state, emphasizing the importance of a sufficient vitamin D supply during pregnancy and sufficient physical activities during the juvenile period to increase bone quality