Magnesium is one of the body's electrolytes, which are minerals that carry an electric charge when dissolved in body fluids such as blood, but the majority of magnesium in the body is uncharged and bound to proteins or stored in bone. (See also Overview of Electrolytes.)
Bone contains about half of the body’s magnesium. Blood contains very little. Magnesium is necessary for the formation of bone and teeth and for normal nerve and muscle function. Many enzymes in the body depend on magnesium to function normally. Magnesium is also related to the metabolism of calcium and the metabolism of potassium.
The level of magnesium in the blood depends largely on how the body obtains magnesium from foods and excretes it in urine and stool and less so on the total body stores of magnesium. The level of magnesium in the blood can become