Literature data on the bioavailability of various Mg forms provide scarce information on the best Mg salt to be used in animal and human supplementation. This study aimed to investigate the bioavailability of different forms of Mg in rats using Mg stable isotopes. Eighty male Wistar rats aged 6 weeks were fed a semi-purified Mg-depleted diet for three weeks. The rats were then randomised into ten groups and received, for two more weeks, the same diet repleted with Mg (550 mg Mg/kg) as: oxide, chloride, sulphate, carbonate, acetate, pidolate, citrate, gluconate, lactate or aspartate. After 10 days of Mg-repleted diet, the rats received orally 1.8 mg of an enriched 26Mg. Faeces and urine were then collected for 4 consecutive days. Isotope ratios in faeces and urine were determined. The Mg absorption values obtained varied from 50% to 67%. Organic Mg salts were slightly more available than inorganic Mg salts. Mg gluconate exhibited the highest Mg bioavailability of the ten Mg salts studied. Urinary 26Mg excretion varied from 0.20 mg to 0.33 mg, and feeding with the organic pidolate, citrate, gluconate and aspartate salts resulted in higher urinary 26Mg excretion than with inorganic salts. Ultimately, 26Mg retention was higher in the rats receiving the organic salts such as gluconate, lactate and aspartate than in those receiving the inorganic salts. Taken together, these results indicate that 26Mg is sufficiently bioavailable from the ten different Mg salts studied in the present experiment, although Mg gluconate exhibited the highest bioavailability under these experimental conditions.
Magnesiumoksidin teho tuplaantui, kun sen sai poretabletista:
Magnesium is suggested to reduce intestinal oxalate absorption and to act as an inhibitor of calcium oxalate crystallization in the urine. However, previous studies have shown only minimal increase in urinary magnesium excretion following oral magnesium supplementation, possibly due to its low bioavailability. This study was performed to examine the bioavailability of magnesium from two different pharmaceutical formulations of magnesium oxide (MgO). Thirteen healthy male volunteers (22-31 years) were recruited from university students and staff, and all completed the study. During the baseline phase, subjects collected two 24-h urines while on their usual diet. Throughout the control and test phases, the subjects consumed a standardized diet calculated according to the recommendations. During the test phases, subjects received two magnesium preparations in a cross-over procedure. With each preparation, MgO-capsules and MgO-effervescent tablets, 450 mg magnesium was supplemented. On the control day and the two test days, fractional urine collection was performed and six corresponding blood samples were taken. In the follow-up phase, subjects continued to take the respective preparation while on their usual diet and collected 24-h urines weekly. With standardized conditions, urinary magnesium excretion increased by 40% after ingestion of the effervescent tablets, and by only 20% after intake of the capsules. The results indicate better bioavailability of magnesium from the effervescent tablets than from the capsules. This may be attributed to the fact that the tablets have to be dissolved in water before ingestion so that magnesium becomes ionized, which is an important precondition for absorption.