Does vitamin D form crystals in the blood with calcium and magnesium? I read on a vitamin-D product (2000NE) that I should not use calcium and magnesium with it, because it can result crystal formation in the blood. I googled, but find anything about this. Is it true? (Somehow I doubt it, but I don't know the exact mechanism how vitamin-D works by building bones. Afaik. there are osteoblasts and osteoclasts which constantly build and degrade the Ca-Mg-PO4 depos, and I assume vitamin-D is just a cofactor of an enzyme or it is required to produce a hormone. I never heard of Ca/Mg - vitamin-D cross-reactions...)

Vitamin D does not bind to Calcium. It is a pre-hormone which is converted to calcitriol. Calcitriol has an intracellular receptor (VDR) that, as a heterodimer with Retinoid-X receptor, regulates gene expression.

I guess the "should not be had together" is because of possible over-absorption of Calcium. There are commercially available supplements (e.g. 1, 2) that have Vit-D + Ca + Mg.