Magnesium is essential to bodily functions. It enables ATP from which most energy is produced in cells. It regulates over 300 biochemical reactions in the body. It is important to the transfer of nutrients through cell walls. It stabilizes the structure of DNA and RNA.
What would happen to a person if some alien micro-organism totally depleted his/her body of magnesium? How quickly would they die? (Yes, there may be a sci-fi story being written here.)