Magnesium Bioavailability and Tolerability Do Not Differ between Two Supplements with Different Release Properties

Magnesium (Mg²⁺) is one of the most frequently supplemented micronutrients. Due to possible gastrointestinal side effects, the European Food Safety Authority and the Institute of Medicine set the upper intake level for Mg²⁺ from supplements to 250 and 350 mg, respectively. Nevertheless, systematic data concerning the tolerability of Mg²⁺ supplements are scarce. The aim of the study was to directly compare the bioavailability and tolerability of two 500 mg Mg²⁺ supplements in a crossover study with duplicate determination. The different release properties were either a direct release (one phase) or a delayed release of the second half (two phases). An open-label, controlled trial with a crossover design, duplicate determination, and one-week washout phases was conducted. The participants ingested the test product after overnight fasting. Blood samples were taken at baseline and after 1, 2, 3, 4, 6, and 8 hours, and urine was collected over a period of 24 hours. The participants were on standardized nutrition during all examination days. There were no significant differences between the test products regarding 24-hour renal Mg²⁺ excretion and area under the curve of serum Mg²⁺ levels for 8 hours. Both test products were well tolerated with a very low frequency of gastrointestinal adverse effects and no significant differences between the test products. The Mg²⁺ bioavailability did not differ between the test products. The supplements examined had the same good tolerability. Both test products are therefore suited to enhance Mg²⁺ supply without relevant side effects.