Background
Magnesium is one of the body’s major electrolytes. As the second most common intracellular cation, it plays a vital role in many cellular metabolic pathways.
Magnesium is required for deoxyribonucleic acid (DNA) and protein synthesis. It is a necessary cofactor for most enzymes in phosphorylation reactions. It is also important for parathyroid hormone synthesis.
The total body content of this central cation is 2000 mEq, or 24 g. The magnesium is distributed in bone (67%), intracellularly (31%), and extracellularly (a mere 1%).
The intracellular concentration is 40 mEq/L, while the normal serum concentration is 1.5-2.0 mEq/L. Of this serum component, 25-30% is protein bound, 10-15% is complexed, and the remaining 50-60% is ionized.
Magnesium is absorbed in the ileum and excreted in stool and urine. The minimum daily requirement of magnesium is 300-350 mg, or 15 mmol; this amount is easily obtainable with a normal daily intake of fruits, seeds, and vegetables because magnesium is a component of chlorophyll and is present in high concentrations in all green plants.
The kidney is the main regulator of magnesium concentrations. Absorption occurs primarily in the proximal tubule and thick ascending limb of the loop of Henle.
Hypermagnesemia is a rare electrolyte abnormality because the kidney is very effective in excreting excess magnesium.