Where is magnesium found in the body?
The average human body contains a total of 25 g of magnesium, which is roughly equivalent to 2000 mEq or 1 mole of magnesium. Nearly 99% of this magnesium is intracellular, with just over half trapped in bone. Only 1% is extracellular, a third of which (2.6 mmol) is present in plasma.
Like calcium, only the ionized fraction of magnesium is metabolically active, and represents 55% to 70% of serum magnesium.
The intracellular magnesium concentration is 10 to 20 mM/L; however, the majority of this magnesium is bound to adenosine triphosphate (ATP), while a smaller potion is bound to nucleotides and proteins. Only 5% of the cytosolic magnesium (0.5 to 1 mM/L) is unbound.