Mg is 1.7–2.3 mg/dL (0.69–0.94 mmol/L). The kidneys regulate the serum magnesium. About 2400 mg of magnesium passes through the kidneys daily, of which 5% (120 mg) is excreted through urine. The loop of Henle is the major site for magnesium homeostasis, and 60% is reabsorbed. Magnesium homeostasis comprises three systems: kidney, small intestine, and bone. In the acute phase of magnesium deficiency there is an increase in absorption in the distal small intestine and tubular resorption in the kidneys. When this condition persists, serum magnesium drops and is corrected with magnesium from bone tissue. The level of intracellular magnesium is controlled through the reservoir in bone tissue. Diagnosis Magnesium deficiency or depletion is a low level of magnesium; it is not easy to measure directly. Typically the diagnosis is based on finding hypomagnesemia, a low magnesium level, which often reflects low body magnesium; however, magnesium deficiency can be present without hypomagnesemia, and vice versa. A plasma magnesium concentration of less than 0.6 mmol/L (1.46 mg/dL) is considered to be hypomagnesemia; severe disease generally has a level of less than 0.50 mmol/L (1.25 mg/dL). Electrocardiogram The electrocardiogram (ECG) change may show a tachycardia with a prolonged QT interval. Other changes may include prolonged PR interval, ST segment depression, flipped T waves, and long QRS duration. Treatments Treatment of magnesium deficiency depends on the degree of deficiency and the clinical effects. Replacement by mouth is appropriate for people with mild symptoms, while intravenous replacement is recommended for people with severe effects. Numerous oral magnesium preparations are available. In two trials of magnesium oxide, one of the most common forms in magnesium dietary supplements because of its high magnesium content per weight, was found to be less bioavailable than magnesium citrate, chloride, lactate or aspartate. Amino-acid chelate was also less bioavailable. Intravenous magnesium sulfate (MgSO4) can be given in response to heart arrhythmias to correct for hypokalemia, preventing pre-eclampsia, and has been suggested as having a potential use in asthma. Food Food sources of magnesium include leafy green vegetables, beans, nuts, and seeds. Epidemiology The condition is relatively common among people in hospital. History Magnesium deficiency in humans was first described in the medical literature in 1934. Plants Magnesium deficiency is a detrimental plant disorder that occurs most often in strongly acidic, light, sandy soils, where magnesium can be easily leached away. Magnesium is an essential macronutrient constituting 0.2-0.4% of plants' dry