School of Pharmacy and Medical Sciences, University of South Australia, Adelaide, South Australia 5001, Australia.
Nutrients. 2010 Sep;2(9):1026-35. doi: 10.3390/nu2091026. Epub 2010 Sep 17.
Animal models fed low calcium diets demonstrate a negative calcium balance and gross bone loss while the combination of calcium deficiency and oophorectomy enhances overall bone loss. Following oophorectomy the dietary calcium intake required to remain in balance increases some 5 fold, estimated to be approximately 1.3% dietary calcium. In the context of vitamin D and dietary calcium depletion, osteomalacia occurs only when low dietary calcium levels are combined with low vitamin D levels and osteoporosis occurs with either a low level of dietary calcium with adequate vitamin D status or when vitamin D status is low in the presence of adequate dietary calcium intake. Maximum bone architecture and strength is only achieved when an adequate vitamin D status is combined with sufficient dietary calcium to achieve a positive calcium balance. This anabolic effect occurs without a change to intestinal calcium absorption, suggesting dietary calcium and vitamin D have activities in addition to promoting a positive calcium balance. Each of the major bone cell types, osteoblasts, osteoclasts and osteocytes are capable of metabolizing 25 hydroxyvitamin D (25D) to 1,25 dihydroxyvitamin D (1,25D) to elicit biological activities including reduction of bone resorption by osteoclasts and to enhance maturation and mineralization by osteoblasts and osteocytes. Each of these activities is consistent with the actions of adequate circulating levels of 25D observed in vivo.
动物模型喂养低钙饮食会导致负钙平衡和明显的骨丢失，而钙缺乏和卵巢切除的结合会增强整体骨丢失。卵巢切除后，为了保持平衡，所需的膳食钙摄入量增加了约 5 倍，估计约为膳食钙的 1.3%。在维生素 D 和膳食钙缺乏的情况下，只有当低钙饮食水平与低维生素 D 水平结合时才会发生骨软化症，而骨质疏松症则发生在膳食钙水平低但维生素 D 状态充足或维生素 D 状态低而膳食钙摄入充足的情况下。只有当维生素 D 状态充足并摄入足够的膳食钙以实现正钙平衡时，才能达到最大的骨结构和强度。这种合成代谢作用不会改变肠道钙吸收，这表明膳食钙和维生素 D 除了促进正钙平衡外，还有其他作用。每个主要的骨细胞类型，成骨细胞、破骨细胞和骨细胞，都能够将 25 羟维生素 D（25D）代谢为 1,25 二羟维生素 D（1,25D），以发挥生物活性，包括减少破骨细胞的骨吸收，并通过成骨细胞和骨细胞增强成熟和矿化。这些活动中的每一个都与体内观察到的足够循环水平的 25D 的作用一致。
