The effect of magnesium on zinc absorption

Multiple dietary components have been demonstrated to influence zinc absorption. The inhibition of zinc absorption by phytate is reportedly augmented by a concurrent high calcium intake. It has been known for some time that calcium and magnesium are mutual biochemical antagonists. This study was designed to test the effect of magnesium on zinc absorption. The study was performed on ten (five male, five female) healthy subjects (x" age - 26 years). Oral doses of zinc and magnesium were 25 mg of zinc (as 110 mg of ZnSO4•7H2O) and 25, 50, and 75 mg of magnesium (as 253.5, 507, and 760.5 mg of MgSO^'7H20), representing Mg/Zn ratios of 1:1, 2:1, and 3:1, respectively. The rate of rise or inhibition in plasma zinc was used as the index of zinc absorption and was assessed at 1/2-, 1-, 2-, and 3-hour intervals post-ingestion. Mean baseline plasma zinc and magnesium values were 88 ug/dl and 2.21 mg/dl, respectively. A significant (P < 0.001) rise in plasma zinc was observed, regardless of the magnesium dosage concomitantly ingested. At the end of 3 hours, the mean rise in plasma zinc for the 1:1, 2:1, and 3:1 ratios of magnesium was 141.3, 125.4, and 140.5 ug/dl, and represented increases of 165%, 147%, and 149% over baseline levels, respectively. Plasma magnesium levels remained relatively constant throughout the 3-hour period. No significant relationships were noted between either the age or sex of the subjects and responses to zinc and magnesium ingestion over time. Magnesium did not appear to influence the absorption of zinc, at least for the three ratios studied.