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Journal of the American College of Nutrition, Vol. 27, No. 2, 349-355 (2008)
Published by the American College of Nutrition

Magnesium Retention in 12 to 48 Month-Old Children

Ian J. Griffin, MD, Mary Frances Lynch, MD, Keli M. Hawthorne, RD, Zhensheng Chen, PhD, Maria Hamzo, BS and Steven A. Abrams, MD

US Department of Agriculture/Agricultural Research Service. Children's Nutrition Research Center (I.J.G., M.F.L., S.A.A.)
Section of Neonatology, Department of Pediatrics (I.J.G., M.F.L., K.M.H., Z.C., M.H., S.A.A.), Baylor College of Medicine and Texas Children's Hospital, Houston, Texas

Address correspondence to: Ian J Griffin, MD, USDA/ARS Children's Nutrition Research Center, 1100 Bates St., Houston, TX 77030. E-mail: lgriffin{at}bcm.edu

Objectives: In adults, adaptation to changes in magnesium intake is largely due to changes in fractional magnesium absorption and urinary magnesium excretion. We sought to examine whether these homeostatic mechanism also occurred in young children.

Methods: Children, 12–48m old were studied (n=30). They were adapted to a home diet representative of their usual magnesium intake for 7d then admitted for a stable isotope study. Children received 5mg Mg-25 intravenously, and 10mg Mg-26 orally (5mg with breakfast and 5mg with lunch). Magnesium absorption was calculated from the relative fractional excretion of the oral and intravenous isotopes in the urine samples. Endogenous fecal magnesium absorption was calculated in a subgroup from the fecal and urinary excretion of the intravenous tracer.

Results: Magnesium intake (mean ± SD; 106 ± 25mg/d) was significantly greater than the Estimated Average Requirement (EAR) described by the Institute of Medicine in the US (65 mg/d, p < 0.0001). Across the range of intake studied, fractional magnesium absorption was significantly (P = 0.0383) but weakly (r2 = 0.144) related to magnesium intake. Absolute magnesium absorption (the product of fractional absorption and intake) significantly increased as intake increased (r2 = 0.566, P < 0.0001). Urinary magnesium excretion was unrelated to magnesium intake (r2 = 0.036, P = 0.31). Endogenous fecal magnesium excretion tended to increase as magnesium intake increased (r2 = 0.312, P = 0.12). Magnesium retention (absolute absorption minus urinary and fecal losses) was positive in 26 of the 30 subjects studied, and was linearly related to magnesium intake (r2 = 0.157, P = 0.0304). A magnesium intake of 52–78 mg/d would appear to be required to meet the needs for absorbed magnesium for half the children at this age range, suggesting that the current EAR is broadly appropriate.

Conclusions: In young children, consuming magnesium intakes typical of the US population, fractional magnesium absorption is a major site of magnesium homeostasis, but magnesium retention increased linearly across the intake range studied. Our results support at EAR for magnesium of 55–80 mg/d and an RDA of 70–100 mg/d.

Abbreviations: EAR = estimated average requirement • RDA = recommended dietary allowance






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