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

Magnesium (Mg) 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 Mg from supplements to 250 and 350 mg, respectively. Nevertheless, systematic data concerning the tolerability of Mg supplements are scarce. The aim of the study was to directly compare the bioavailability and tolerability of two 500 mg Mg 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 Mg excretion and area under the curve of serum Mg 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 Mg bioavailability did not differ between the test products. The supplements examined had the same good tolerability. Both test products are therefore suited to enhance Mg supply without relevant side effects.