Magnesium and calcium are fundamental nutrients that need to be in balance with each other in order for you to fully experience good health. Their importance on a cellular level is critical. Calcium and magnesium are like opposite sides of a coin. Calcium excites nerves, while magnesium calms them down. Calcium makes muscles contract. Magnesium is necessary for muscles to relax. Calcium is needed for blood clotting, but magnesium keeps the blood flowing freely.