Magnesium is an important micronutrient that many parts of your body – including your nervous system, your muscles, your heart, your bones and immune system – need in order to function properly. The adult human body contains about 25 grams, with about half stored in the bones, while the rest can be found in soft tissues, bodily fluids and muscles. Most adults in the US do not meet that daily target through their diet. And selecting a supplement is no easy task, as a bewildering number of products can be found on the market.