Vitamin D and osteoporosis

The major effects of vitamin D on the skeleton are recognized in deficiency states as the failure of normal mineralization of bone. The presence of the vitamin D receptor (VDR) in bone cells suggests direct effects on bone. These receptors are expressed in osteoblasts and in immature cells of the osteoclast precursor lineage. It was proposed some time ago that the effect of the active vitamin D metabolites on osteoclasts was indirect via osteoblasts. Treatment with the combination of calcium and vitamin D prevents bone loss and results in small increases in bone mineral density (BMD) at most sites. For long-term maintenance of BMD up to five years, the combination of calcium and vitamin D appears to be better than calcium alone. These skeletal benefits of calcium and vitamin D may be maintained at some, but not all, skeletal sites after withdrawal. However, there are no data to suggest that vitamin D alone is effective in maintaining or in increasing BMD. The addition of vitamin D to calcium is also likely to reduce the risk of falling, particularly in winter, in patients with a history of falling and vitamin D insufficiency. This may result in a reduction of falls-related fractures.