Absorption magnesium

FOS and oligofuctose are fructose oligomers that are either produced by enzymic conversion of sugar or extracted from chicory, as inulin, and then hydrolysed. These products behave as soluble fibres and prebiotics. In acid conditions, they can hydrolyse, but are usually sufficiently stable for short-shelf-life juices, near-water products with low acid levels or powdered soft drinks. Prebiotic activity varies with preparation and required daily dose can be as low as 2.5-5.0 g/day for shorter chain FOS preparations (DP 2 1). Some positive effects on magnesium absorption and calcium absorption (in some populations) have also been shown (Beghin Meiji, 2001). 

Measurements of True Magnesium Absorption. Appearance of a single ingested isotope in the plasma or urine can not provide a quantitative estimate of fractional absorption of a mineral without concomitant measurement of Isotope exchange between the mineral in the plasma and other body compartments 2A). Table IV shows the levels of urinary Mg from an intravenous injection that accompanied an oral dose of 50 mg Mg. Radioactivity was determined in 15 ml urine with a relative S.D. of < 1% in composites collected at Intervals up to 24 hours, and with < 4% in the 24-48 h collection. The relative standard deviations for Mg measurements were consistently higher, reaching unacceptable levels in samples taken after 12 hours following the test meal. 

At present, uses of Mg are restricted to objectives that can be attained by oral Isotope administration onlyt One of these Is the measurement of "true magnesium absorption in which Mg is given orally, and Mg by Injection. "True absorption Is then computed either by estimation of the ratio %g Mg in urine or, more precisely, by measuring net absorption Csubtractlon of fecal exr ... 

Fig. 17. The depressive effect of phosphate on magnesium absorption (compare with Fig. 4). Phosphate concentrations given as phosphorus (from reference Z4).

Hunt, C. D., Herbel, J., and Nielsen, E H. (1997). Metabolic responses of postmenopausal women to supplemental dietary boron and aluminum during usual and low magnesium Intake Boron, calcium, and magnesium absorption and retenton and blood mineral concentrations. Am. /. Cfin. Nuir, 65, 803-813. 

The results of an in vitro study on immortalized mouse distal convoluted tubule cells have suggested that aminoglycosides act through an extracellular polyvalent cation-sensing receptor and that they inhibit hormone-stimulated magnesium absorption in the distal convoluted tubule (80). 

De Swart PM JR, Busemann Sokole E, Wilmink JM. The interrelationship of calcium and magnesium absorption in idiopathic hypercalciuria and renal calcium stone disease. J Urol 1998 159 669-72. 

Human studies have shown increased lu-inary excretion and decreased calcium and magnesium absorption in women administered the minerals and caffeine at the same time (Bergman et al. 1990 Heaney and Recker 1982), although an epidemiological study of approximately 1000 people over age 30 indicated a higher bone mineral density in persons who had habitually consumed tea for 19 years or more, as compared with nonhabitual tea drinkers (Nesher et al. 2003). 

Green tea may reduce the absorption of iron (Samman et al. 2001). Caffeine may decrease calcium and magnesium absorption (Bergman et al. 1990 Heaney and Recker 1982). 

Studies in humans have indicated that increasing the level of dietary protein enhances magnesium absorption [40,41]. Excessive dietary fat has been shown to impair magnesium absorption due to the formation of insoluble magnesium soaps [42,43]. Readily available carbohydrates such as lactose may enhance magnesium intestinal absorption [44,45], while excess dietary fiber may decrease magnesium absorption in humans [46]. The ionophores monensin and lasalocid have both been shown to enhance magnesium absorption in steers [47). 

Hypernatremia and hypercalcemia can cause a reduction in magnesium absorption. 

Bohn, T., Walczyk, T., Davidsson, L., Pritzkow, W., Klingbeil, P., Vogl, J., and Hurrell, R.F. (2004) Comparison of urinary monitoring, faecal monitoring and erythrocyte analysis of stable isotope labels to determine magnesium absorption in human subjects. Br. J. Nutr., 91 (1), 113-120. 

Apparent magnesium absorption can be determined even with basic quadru-pole-based ICP-MS instruments, which can deliver precisions of 0.2-0.5% RSD for measuring the Mg/ Mg and Mg/ " Mg isotope ratios [208, 209], which is similar to what can be achieved using sector field ICP-MS [210] or collision cell ICP-MS [211]. Such precisions require isotope doses of the order of 20-50 mg to reach enrichments in the percent range in the collected fecal material. This compares with a dietary magnesium intake of about 300 mg per day. 

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