A large section of the North American population is not meeting recommended intakes for magnesium (Mg). Supplementation and consumption of Mg-fortified foods are ways to increase intake. Currently, information on Mg bioavailability from different compounds and their efficacy in improving Mg status is scant. This study compared the relative ability of inorganic and organic Mg compounds to preserve the Mg status of rats when fed at amounts insufficient to retain optimal Mg status. Male Sprague-Dawley rats (n=12/diet group) were fed one of eight test diets supplemented with phytic acid (5 g/kg diet) and low levels of Mg (155 mg elemental Mg/kg diet) from Mg oxide, Mg sulphate, Mg chloride, Mg citrate, Mg gluconate, Mg orotate, Mg malate or ethylenediaminetetraacetic acid disodium Mg salt for five weeks. Rats were also fed three control diets that did not contain added phytic acid but were supplemented with 500 (NMgO, normal), 155 (LMgO, low) or 80 (DMgO, deficient) mg of Mg per kg diet as Mg oxide. Mg concentrations in femur, serum and urine showed a graded decrease in rats fed the control diets with lower Mg. Mg concentrations did not differ (P≥0.05) between rats fed the different test diets. Addition of phytic acid to the diet did not affect the Mg status of the rats. The results indicate that any differences in the Mg bioavailability of the compounds were small and physiologically irrelevant.
Keywords: bioavailability; magnesium; phytic acid; rat.