Submitted to: Journal of American College of Nutrition
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 6/11/2007
Publication Date: 4/20/2008
Citation: Griffin, I.J., Lynch, M.F., Hawthorne, K.M., Chen, Z., Hamzo, M., Abrams, S.A. 2008. Magnesium retention in 12 to 48 month-old children. Journal of American College of Nutrition. 27(2):349-355. Interpretive Summary: Adults adapt to changes in magnesium balance through changes in absorption and excretion. Magnesium balance adaptation is important due to the need to obtain enough magnesium in the body to support the growth of bones and other tissues. We studied children, 12-48 months old, to find out if they also adapt the same way. Children received magnesium stable isotopes orally and intravenously with breakfast and lunch on the day of the study, and urine and stool collections were obtained to determine absorption and excretion. Intake on the study day was based on the child’s individual dietary history as reported to the study dietitian. We found that the average magnesium intake was significantly greater than the Estimated Average Requirement established by the Institute of Medicine. Young children who consume typical US magnesium intakes use fractional absorption to regulate magnesium homeostasis; however, magnesium retention increased across the intake range studied. Our results support an Estimated Average Requirement, recommendation of 55-80 mg/d, and a Recommended Daily Allowance of 70-110 mg/d, as these levels appear to meet the needs for absorbed magnesium for half the children in this age range.
Technical Abstract: 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 mechanisms also occur in young children. Children, 12–48 m old, were studied (n=30). They were adapted to a home diet representative of their usual magnesium intake for 7 d, and then admitted for a stable isotope study. Children received 5 mg Mg-25 intravenously, and 10 mg Mg-26 orally (5 mg with breakfast and 5 mg 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. Magnesium intake (mean +/- SD; 106 +/- 25 mg/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. 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 average requirement (EAR) for magnesium of 55–80 mg/d and an RDA of 70–100 mg/d.