Magnesium is an essential mineral and cofactor in over 300 enzymatic reactions including ATP synthesis, muscle contraction, nerve transmission, and blood glucose regulation. About 99% is stored in bone and soft tissue; only 1% circulates in blood, so serum magnesium is a poor reflection of total body stores.

Low serum magnesium is most commonly caused by inadequate dietary intake, gastrointestinal losses, and renal wasting from diuretics or alcohol. Symptoms of deficiency include muscle cramps, fatigue, irritability, headaches, sleep disturbance, and cardiac arrhythmias.