There is currently no reliable indicator of magnesium status. The magnesium tolerance test, which basically determines magnesium retention (using 24-h urine collection) following the intravenous administration of magnesium, is considered to be the gold standard (1)*. If this method is a good indicator of hypomagnesemia in adults, it appears to be poorly sensitive to changes in magnesium status in healthy people. Moreover, the method is invasive and cumbersome, and thus difficult to use routinely (2)**. Another method to assess magnesium status is through measurements of plasma ionized magnesium, which represents the physiologically active form of magnesium. However, it is unknown whether plasma ionized magnesium reflects body stores (2)**.
In practice, magnesium status is usually determined through assessments of dietary magnesium intake, serum magnesium concentration, and/or urinary magnesium concentration (2)**. However, each of these indicators has limitations. Although predominantly used in epidemiological studies and the sole indicator available to clinicians, serum magnesium concentration has been found to poorly respond to magnesium supplementation. Regarding dietary intakes of magnesium, about 30 to 40% of ingested magnesium is absorbed, yet absorption varies with the amount of magnesium ingested and with the food matrix composition. Finally, a state of magnesium deficiency has not been associated with a clear cutoff concentration of magnesium in the urine. Urinary magnesium concentration fluctuates rapidly with dietary intakes, but measurements of 24-hour urinary magnesium can be used in addition to other indicators to assess population status. Presently, a combination of all three markers — dietary, serum, and urinary magnesium — may be used to get a valid assessment of magnesium status (reviewed in 2)**.
In practice, magnesium status is usually determined through assessments of dietary magnesium intake, serum magnesium concentration, and/or urinary magnesium concentration (2)**. However, each of these indicators has limitations. Although predominantly used in epidemiological studies and the sole indicator available to clinicians, serum magnesium concentration has been found to poorly respond to magnesium supplementation. Regarding dietary intakes of magnesium, about 30 to 40% of ingested magnesium is absorbed, yet absorption varies with the amount of magnesium ingested and with the food matrix composition. Finally, a state of magnesium deficiency has not been associated with a clear cutoff concentration of magnesium in the urine. Urinary magnesium concentration fluctuates rapidly with dietary intakes, but measurements of 24-hour urinary magnesium can be used in addition to other indicators to assess population status. Presently, a combination of all three markers — dietary, serum, and urinary magnesium — may be used to get a valid assessment of magnesium status (reviewed in 2)**.
References
(1)*. Volpe SL. Magnesium. In: Erdman Jr. JW, Macdonald IA, Ziegler EE, eds. Present Knowledge in Nutrition. 10th ed: ILSI Press; 2012:459-474.
(2)** Costello RB, Nielsen F. Interpreting magnesium status to enhance clinical care: key indicators. Curr Opin Clin Nutr Metab Care. 2017;20(6):504-511. (PubMed)
(1)*. Volpe SL. Magnesium. In: Erdman Jr. JW, Macdonald IA, Ziegler EE, eds. Present Knowledge in Nutrition. 10th ed: ILSI Press; 2012:459-474.
(2)** Costello RB, Nielsen F. Interpreting magnesium status to enhance clinical care: key indicators. Curr Opin Clin Nutr Metab Care. 2017;20(6):504-511. (PubMed)