据一项新的研究报告，维生素D缺乏可能会加快人骨骼的老化，而这又会增加发生骨折的风险。这些研究发现表明，缺乏该“日照维生素”不仅会降低骨密度，而且还会影响骨骼的质量。维生素D是钙质吸收及其被骨骼摄取所必不可少的。没有钙，骨骼无法矿质化或进行重建并变得更加强固。缺乏维生素D的人有罹患多种疾病的风险，其中包括骨质疏松。Bj?rnBusse及其同事对采自30名参与者（他们中有一半缺乏维生素D）的骨骼样本进行了分析。他们采用了最先进的技术——其中包括基于同步辐射的微计算机断层扫描——在最小尺度来描述从纳米到微米的骨骼质量。研究人员能够在一系列的测试中实时追踪骨骼开裂的进展并检测了发生开裂的阻力。
正如所预期的，他们发现维生素D缺乏的受试者在其骨骼的表面有着较少的矿质化。但在骨表面以下的骨骼实际上有着更多的矿质化。它还显示了较老的及较脆的骨骼的结构特点。研究人员注意到，这些矿质化骨岛被一个胶原性边界所包围，而这会阻止它们被适当地改建。在被切断了破骨细胞——这些细胞在正常情况下会对骨骼进行改建——的供应时，这些矿质化骨的孤立部分开始老化，而整体的骨骼矿质化则会因为钙的缺乏而减少。这些结果显示，在维生素D缺乏时会出现老化骨骼区域、骨骼质量降低并导致骨折风险增高。阐明人类骨骼结构的复杂性可能会让人们对防止或治疗骨折的更有效的方法有所了解。一则相关的《焦点》文章对这些结果进行了讨论。（生物谷 Bioon.com）
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Sci. Transl. Med. DOI: 10.1126/scitranslmed.3006286
Vitamin D Deficiency Induces Early Signs of Aging in Human Bone, Increasing the Risk of Fracture
Björn Busse1,2,*, Hrishikesh A. Bale2, Elizabeth A. Zimmermann1,2,3, Brian Panganiban2, Holly D. Barth2,3, Alessandra Carriero2, Eik Vettorazzi4, Josef Zustin5, Michael Hahn1, Joel W. Ager III2, Klaus Püschel6, Michael Amling1 and Robert O. Ritchie
Vitamin D deficiency is a widespread medical condition that plays a major role in human bone health. Fracture susceptibility in the context of low vitamin D has been primarily associated with defective mineralization of collagenous matrix (osteoid). However, bone’s fracture resistance is due to toughening mechanisms at various hierarchical levels ranging from the nano- to the microstructure. Thus, we hypothesize that the increase in fracture risk with vitamin D deficiency may be triggered by numerous pathological changes and may not solely derive from the absence of mineralized bone. We found that the characteristic increase in osteoid-covered surfaces in vitamin D–deficient bone hampers remodeling of the remaining mineralized bone tissue. Using spatially resolved synchrotron bone mineral density distribution analyses and spectroscopic techniques, we observed that the bone tissue within the osteoid frame has a higher mineral content with mature collagen and mineral constituents, which are characteristic of aged tissue. In situ fracture mechanics measurements and synchrotron radiation micro–computed tomography of the crack path indicated that vitamin D deficiency increases both the initiation and propagation of cracks by 22 to 31%. Thus, vitamin D deficiency is not simply associated with diminished bone mass. Our analyses reveal the aged nature of the remaining mineralized bone and its greatly decreased fracture resistance. Through a combination of characterization techniques spanning multiple size scales, our study expands the current clinical understanding of the pathophysiology of vitamin D deficiency and helps explain why well-balanced vitamin D levels are essential to maintain bone’s structural integrity.
