There is currently no reliable single indicator of magnesium status. The magnesium tolerance test — which measures magnesium retention through 24-hour urine collection following intravenous magnesium administration — is considered the gold standard (1)*. While this method is a good indicator of hypomagnesaemia in adults, it appears to be poorly sensitive to changes in magnesium status in healthy individuals. Moreover, the test is invasive and cumbersome, making it difficult to use routinely (2)**.
Another approach is to measure plasma ionised magnesium, which represents the physiologically active form of the mineral. However, it remains unclear whether plasma ionised magnesium accurately reflects total body stores (2)**.
In practice, magnesium status is usually assessed through a combination of dietary intake, serum magnesium concentration, and/or urinary magnesium excretion (2)**. Each of these indicators has limitations. Although serum magnesium is the most commonly used marker in epidemiological studies and the only indicator routinely available to clinicians, it has been shown to respond poorly to magnesium supplementation.
Dietary assessment is also challenging: approximately 30–40% of ingested magnesium is absorbed, but this varies depending on the amount consumed and the composition of the food matrix. Urinary magnesium concentration fluctuates rapidly with dietary intake and does not have a clear cutoff point associated with deficiency. However, 24-hour urinary magnesium measurements can complement other indicators when assessing population-level status.
Currently, a combination of all three markers — dietary, serum, and urinary magnesium — is recommended for a valid assessment of magnesium status (reviewed in 2)**..
Another approach is to measure plasma ionised magnesium, which represents the physiologically active form of the mineral. However, it remains unclear whether plasma ionised magnesium accurately reflects total body stores (2)**.
In practice, magnesium status is usually assessed through a combination of dietary intake, serum magnesium concentration, and/or urinary magnesium excretion (2)**. Each of these indicators has limitations. Although serum magnesium is the most commonly used marker in epidemiological studies and the only indicator routinely available to clinicians, it has been shown to respond poorly to magnesium supplementation.
Dietary assessment is also challenging: approximately 30–40% of ingested magnesium is absorbed, but this varies depending on the amount consumed and the composition of the food matrix. Urinary magnesium concentration fluctuates rapidly with dietary intake and does not have a clear cutoff point associated with deficiency. However, 24-hour urinary magnesium measurements can complement other indicators when assessing population-level status.
Currently, a combination of all three markers — dietary, serum, and urinary magnesium — is recommended for 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)