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Vitamin D acts in a way which to me is counterintuitive. It functionally supplemets Parathormone. It in the intestinal tract steps up calcium absorption by altering nuclear gene expression and also prevents calcium excretion in kidneys. All of this is understandable. But it also, like parathormone, steps up osteoclast action in bone (actually steps up both osteoclast and osteoblast, but the osteoclast action is increased more to result in net bone resorption). This means that Vitamin D increases blood calcium level by increasing bone resorption.

Then how does Vitamin D help in improving bone density, bone strength and prevent rickets or osteoporosis? All of these would require bone deposition rather than resorption.

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yes there are some colflicting theories.. This article says that Vit-D actually inhibits osteoclastogenesis. What I can say about it is that the action of Vit-D should be studied in a systems perspective. It may be the effect of dynamics. It allows calcium absorption, and its deficiency would cause reduced calcium leading to reduced bone-mineralization as seen in rickets. However, it also affects resorption and active modeling of the bone. It is important to take other factors (hormones etc) into consideration. –  WYSIWYG Jan 9 at 6:26
and thats where mathematical models are useful –  WYSIWYG Jan 9 at 9:30
The one which is yet to be built :P –  WYSIWYG Jan 10 at 7:11
@WYSIWYG Won't be long. I am already learning Python! –  Satwik Pasani Jan 10 at 8:04
well.. i would suggest that you learn Matlab as well.. The numpy module of python does support numerical computations but matlab has optimized solvers for different types of equations. Having said that, I love python too :) –  WYSIWYG Jan 10 at 9:18
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