There are tests that you can order to take a mineral assay of the body, which would be most helpful, especially if you have a chronic or degenerative condition. I would not bother with vitamin supplementation, as the body produces what it needs IF it is properly hydrated, and has a sufficient supply and proper spectrum of minerals. Lack of sufficient hydration is often a greater problem than vitamins or minerals, not only due to the liquidness of water as a transport medium, but also for the discrete electrical value that is available from it through molecular hydrogen, as well as molecular oxygen.
RE: Magnesium Replenishment: Spreading the Word and Getting the 'Point'