The aim of the present study was to compare the magnesium bioavailability from four mineral waters with different types of mineralization (e.g. SO 42- , HCO 3− , calcium) with the magnesium bioavailability from bread and from a magnesium supplement. A single-center, randomized, controlled trial with a crossover design with 22 healthy men and women was conducted at the Institute of Food Science and Human Nutrition, Leibniz University Hannover, Germany. The participants consumed the six test products providing 100 mg of magnesium each on six examination days with a one-week washout phase in between. The primary outcome variables were the 24 h urinary magnesium excretion, the 24 h urinary magnesium/creatinine ratio, and the area under the curve of serum magnesium levels for 10 h (AUC 0-10h ). No significant differences among groups were observed for either 24 h urinary magnesium excretion or 24 h urinary magnesium/creatinine ratio. Likewise, statistical group comparisons of AUC 0-10h for serum magnesium levels revealed no significant differences among the treatment groups. Accordingly, given equivalent magnesium availability from all test products, neither SO 42- content nor the content of HCO 3− or of calcium influenced the bioavailability of magnesium. Thus, mineral water with higher concentrations of magnesium constitutes a calorie-free magnesium source that contributes to optimal magnesium supply.