Background: Information on the bioavailability of the essential mineral Mg2+ is sparse.
Objective/Method: Evaluation of the present knowledge on factors influencing the bioavailability
and intestinal absorption of Mg2+.
Results: Mg2+ is absorbed via a paracellular passive and a transcellular active pathway that involves
TRPM6/7 channel proteins. The bioavailability of Mg2+ varies within a broad range, depending
on the dose, the food matrix, and enhancing and inhibiting factors. Dietary factors impairing
Mg2+ uptake include high doses of other minerals, partly fermentable fibres (e.g., hemicellulose),
non-fermentable fibres (e.g., cellulose, lignin), phytate and oxalate, whereas proteins, medium-
chain-triglycerides, and low- or indigestible carbohydrates (e.g., resistant starch, oligosaccharides,
inulin, mannitol and lactulose) enhance Mg2+ uptake. The Mg2+ dose is a major factor
controlling the amount of Mg2+ absorbed. In principle, the relative Mg2+ uptake is higher when the
mineral is ingested in multiple low doses throughout the day compared to a single, large intake of
Mg2+. The type of Mg2+ salt appears less relevant than is often thought. Some studies demonstrated
a slightly higher bioavailability of organic Mg2+ salts compared to inorganic compounds
under standardized conditions, whereas other studies did not.
Conclusion: Due to the lack of standardized tests to assess Mg2+ status and intestinal absorption,
it remains unclear which Mg2+ binding form produces the highest bioavailability. The Mg2+ intake
dose combined with the endogenous Mg2+ status is more important. Because Mg2+ cannot be
stored but only retained for current needs, a higher absorption is usually followed by a higher excretion
of the mineral.