Vitamin D: Effects on Bone Metabolism

By | October 19, 2011

Notice the scalloping of the endplates a L3 & L4 and the compression fracture at T12 in this osteoporotic spine.

Before examining the influence of vitamin D, it is essential to understand the underlying baseline metabolism of bone. Most people think of bone as static structures, like the steel beams and girders of modern skyscrapers, which provide support for the rest of the body. But the truth is that bones are dynamic structures, which are constantly rebuilding themselves and adapting to life stresses. This allows bones to grow, repair fractures and strengthen bones or parts of bones that are responding to above normal levels of stress. It would be equivalent to the steel inner structure of a building constantly repairing and rebuilding itself.

The effects of vitamin D on bone metabolism are complex. In conjunction with calcitonin it stimulates osteoblasts to form new bone, but it also works in conjunction with parathyroid hormone to increase osteoclast activity, which leads to the breakdown of bone. Depending on the balance of parathyroid hormone and calcitonin, increasing vitamin D levels might actually favor bone reabsorption and worsen the problem of osteoporosis, a major contributor to chronic pain in the elderly. Multiple studies of vitamin D supplementation have shown only modest and inconsistent benefits in the treatment of osteoporosis except in cases of moderate to severe deficiency. Even more interesting some studies have shown improvements in long bones, but not the spine and others the exact opposite. Clearly other factors are involved.

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