Balance data obtained since 1997 indicate that the Estimated Average Requirement and Recommended Dietary Allowance for magnesium should be 175 and 250 mg/d, respectively, for 70 kg healthy individuals, and increase or decrease based on body weight. Urinary excretion data from balance studies indicate that 40 to 80 mg (1.65 to 3.29 mmol) Mg/day are excreted when magnesium intakes are <250 mg/day, and 80 to 160 mg/day (3.29 to 6.58 mmol) when intakes are >250 mg/day. The change in urinary magnesium excretion with the change in dietary magnesium intake occurs within a few days. Thus, urinary magnesium would be most useful for population studies. Metabolic unit depletion/repletion experiments show that serum magnesium concentrations decrease only after a prolonged depletion if an individual starts with an adequate magnesium status. Individuals with serum magnesium concentrations in excess of 0.75 mmol/L (1.82 mg/dL), or as high as 0.85 mmol/L (2.06 mg/dL), might be magnesium-deficient because such individuals respond to magnesium supplementation. A combination of a dietary intake <250 mg /day, urinary excretion <80 mg (3.29 mmol)/day, and serum magnesium concentration < 0.85 mmol/L (2.06 mg/dL) and preferably <0.80 mmol/L (1.94 mg/dL) could indicate that an individual would respond to magnesium supplementation.
Keywords: balance; deficiency; requirements; serum concentration; urinary excretion.