Magnesium is an important macromineral needed by humans in gram amounts for optimal health. Magnesium is involved in all enzymes utilising ATP and is therefore vitally important in energy production. Magnesium is also needed for proper muscle contraction and relaxation and deficiency has been linked to myocardial infarction, cramps, tremors and tetany. Magnesium is found in high concentrations in whole grains and green leafy vegetables, but decreasing intakes of these foods have caused insufficient magnesium intakes in many parts of the World. In one French study, 77% of women and 72% of men had dietary intakes that were lower than the recommended intakes for France. The absorption of magnesium has been well studied, and generally magnesium is well absorbed even in inorganic forms such as magnesium oxide. Mineral water is a good source of magnesium and can contain up to 100 mL per L of magnesium from some sources.
Researchers1 have investigated the absorption of magnesium from mineral water in healthy women using labelled magnesium. Stable magnesium isotopes of magnesium (25Mg and 26Mg) were administered to subjects along with mineral water (500 mL) both with (26MgSO4) and without (26MgSO4) a meal. The researchers measured the magnesium in the faeces of the subjects to determine the magnesium absorption and magnesium retention was measured via analysis of urinary magnesium concentrations. The absorption of magnesium from the mineral water was 45.7%, but this increased to 52.3 % when the water was consumed with a meal. The retention of magnesium was 37.4%, but this increased to 41.5% when the water was taken with a meal. These results show that eating a meal with magnesium rich mineral water increases relative absorption by 14.4% and retention by 11.0%.
Many factors can influence the absorption of minerals from the diet. Generally, digestion speed is determined by the content of protein in the lumen of the gut, as food is contained within the stomach until most of the protein has been digested to di- and tri-peptides. Consuming a mixed meal that contains protein is therefore an effective way to slow transit of chyme through the gut. Increased transit speed may allow for increase absorption of certain minerals as there is a greater probability that the mineral will come into contact with the necessary transporters in the brush border. This is the likely reason for the increased absorption of magnesium with a meal. The composition of the meal can also be important in mineral absorption as evidence suggests that carbohydrate such as lactose, fructose and glucose, may increase magnesium absorption if taken concomitantly.
RdB
