Magnesium is a jack-of-all-trades nutrient, participating in a vital way in many key functions like bone health, normal muscle function, and normal protein synthesis.*
Although Magnesium is found in many foods, it is easily removed by refining, processing and cooking. Most of us do not get what we are supposed to out of our diet. In fact, more than half of adults aren't meeting their daily magnesium needs through diet alone.*
You need a big amount of Magnesium compared to other essential micronutrients, second only to Calcium. That means it usually takes an entire pill to get a decent amount, no matter which form is used. That translates to more and/or larger pills, which most people do not want.
Magnesium frequently interacts poorly with other nutrients, blocking some and being blocked by others. Certain forms are well-absorbed, and others are not. The difference between just enough and too much can make it a tricky nutrient to formulate within a multivitamin.*