Bone geometry and tissue material properties jointly govern whole-bone structural behavior. While the role of geometry in structural behavior is well characterized, the contribution of the tissue material properties is less clear, partially due to the multiple tissue constituents and hierarchical levels at which these properties can be characterized. Our objective was to elucidate the contribution of the mineral phase to bone mechanical properties across multiple length scales, from the tissue material level to the structural level.
Vitamin D exerts antiproliferative, prodifferentiation, and proapoptotic effects on nonclassic target tissues such as breast. Blood levels of 25-hydroxyvitamin D [25(OH)D], the most sensitive indicator of vitamin D status, are inversely correlated with breast cancer risk; however, a causal relationship between vitamin D deficiency and breast cancer growth in bone has not been assessed.
The Cyp27b1 enzyme (25-hydroxyvitamin D-1-hydroxylase) that converts 25-hydroxyvitamin D into the active metabolite, 1,25-dihydroxyvitamin D3 [1,25(OH)2D3], is expressed in kidney but also in other cell types such as chondrocytes. This suggests that local production of 1,25(OH)2D3 could play an important role in the differentiation of these cells.