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Vitamin D has a significant role in calcium homeostasis and metabolism. Its discovery was due to effort to find the dietary substance lacking in children with rickets (the childhood form of osteomalacia).[12] Vitamin D supplements are given to treat or to prevent osteomalacia and rickets.

taken from the Wikipedia article: https://en.wikipedia.org/wiki/Vitamin_D

It should be taken with vitamin K2. The theory is that it aids calcium absorption into bones rather than dumping into arteries.

https://www.ncbi.nlm.nih.gov/pmc/articles/PMC4566462/

Can't quote from memory but there is substantial evidence that this is not a problem unless you're taking massive doses (tens of thousands of IU) on a daily basis for a lengthy period. Naturally those interested should check this out for themselves.