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Magnesium-Verbindungen. Aufnahme, Funktionen und therapeutische Aspekte
Abstract
Magnesium ist nach dem Kalium das mengenmäßig zweithäufigste intrazelluläre mineralische Element in unserem Körper. Aufgrund seiner vielfältigen Funktionen im Körper führt eine unzureichende Versorgung an Magnesium zu einem breiten Spektrum an Mangelsymptomen. Der Magnesium-Haushalt des Körpers wird durch Resorption aus dem Darm, Ausscheidung über den Stuhl und den Urin sowie Einlagerung oder Freisetzung in das bzw. aus dem Skelett reguliert. Die Resorption von Magnesium erfolgt über den kompletten Darm durch zwei verschiedene Prozesse, zum einen Carrier-vermittelt, zum anderen parazellulär durch passive Diffusion. Die Resorptionsrate aus der Nahrung liegt normalerweise bei 35 bis 55 %. Bei fettreicher Nahrung oder der Aufnahme verschiedener Nahrungsinhaltsstoffe, die die Magnesium-Resorption hemmen wie Phosphat, Phytat oder Oxalat, kann sie aber deutlich reduziert sein. Für die Wirksamkeit von Magnesium-Präparaten spielt die intestinale Bioverfügbarkeit des Magnesiums eine entscheidende Rolle. Organische Magnesium-Verbindungen wie das Citrat, Aspartat, Aspartat-hydrochlorid, Gluconat oder Aminosäurekomplexe haben eine deutlich höhere Bioverfügbarkeit als anorganische Magnesium-Salze wie das Carbonat, Oxid oder Sulfat (mit Ausnahme von Chlorid). Organische Magnesium-Verbindungen sind als Supplemente daher den weniger gut resorbierbaren anorganischen Verbindungen wie Magnesiumoxid oder -carbonat vorzuziehen.
... As constant mineral element in the human body and contributing to a variety of metabolic processes magnesium features excellent biocompatibility (Eder, 2009). Furthermore, mechanical properties and degradation behavior of Mg outperform biodegradable polymers. ...
Currently, only a few magnesium alloys have been approved for implant applications. For biomedi-cal purposes, the choice of the alloying elements is a critical parameter and rare earth elements have been proven to be mechanically suitable and biologically tolerable. In this comprehensive study, tailoring the mechanical properties of binary Mg-Gd alloys by indirect extrusion is shown to obtain a property profile that is applicable to different biomedical applications. Mg-2Gd, Mg-5Gd and Mg-10Gd were solid solution treated before extrusion. For each alloy various combinations of extrusion temperature and speed were applied. Resulting effects of alloy composition and processing on microstructure development, texture evolution, mechanical properties and degradation behaviour were investigated. Grain sizes and corresponding textures were adjusted by the extrusion parameters. Despite minor changes in the texture, grain boundary strengthening effects were confirmed for all alloys in accordance with the Hall-Petch relationship. The alloy composition contributed to the mechanical properties by solid solution strengthening and a combination of texture changes and slip activities. Consequently, mechanical properties can be tailored within a wide range resulting in tensile yield strengths of 90 - 200 MPa (ultimate tensile strengths 180 – 280 MPa) and compressive yield strengths of 80 - 220 MPa (ultimate compressive strengths 300 – 450 MPa) with elongations of 10 - 45%. Low degradation rates in the range of 0.2 mm/year were determined for all alloys. Degradation was only slightly influenced by the alloy composition but not affected by pro-cessing. Overall, the properties of Mg-Gd determined in this work appear to be suitable to future implant applications.
The purpose of this study was to measure magnesium absorption over the wide range of intakes to which the intestine may be exposed from food and/or magnesium-containing medications. Net magnesium absorption was measured in normal subjects after they ingested a standard meal supplemented with 0, 10, 20, 40, and 80 mEq of magnesium acetate. Although absorption increased with each increment in intake, fractional magnesium absorption fell progressively (from 65% at the lowest to 11% at the highest intake) so that absorption as a function of intake was curvilinear. This absorption-intake relationship was almost perfectly represented by an equation containing a hyperbolic function plus a linear function. Our results are statistically compatible with a magnesium absorption process that simultaneously uses a mechanism that reaches an absorptive maximum, plus a mechanism that endlessly absorbs a defined fraction (7%) of ingested magnesium. Compared to previous studies of calcium absorption, much less magnesium that calcium was absorbed at intakes above 8 mEq/meal, apparently due to greater restriction of intestinal permeability to magnesium. We also found that magnesium from a high magnesium-containing food source, almonds, was just as bioavailable as from soluble magnesium acetate. In contrast, magnesium absorption from commercially available enteric-coated magnesium chloride was much less than from magnesium acetate, suggesting that enteric coating can impair magnesium bioavailability.
Magnesium deficiency can occur in several diseases. such
as malabsorption syndromes, diabetes mellitus and renal
disorders. It can be treated with oral magnesium compounds,
of which several preparations are currently available:
various complex salts, and the oxide or hydroxide of
magnesium [1]. In the present study, two formulations of
magnesium-L-asparate HCI (Magnesiocard® tablets and
Magnesiocard® granules, Verla-Phann, FRG) were compared with magnesium-oxide (Magnetrans® forte capsules, Fresenius, FRG) with respect to bioavailability, tolerability, and stool frequency.
The three magnesium preparations were each administered in an open manner to 3 groups of 8 healthy volunteers according to a parallel group design. The groups of 4 males and 4 females each were comparable with regard to age, height and body weight. After a control and a placebo period of one week, 60 mEq/d and 90 mEq/d magnesium were administered for 7 days each. No special diet was given. Cumulative urinary magnesium excretion was used to assess magnesium absorption [2. 3]. Plasma and urine concentrations of magnesium. potassium and
calcium were measured by atome emission spectromtryusing a Spectraspan SR (ARL). Urine pH was assessed with indicator strips (Spezialindikator pH 4.0-7.0. Merck. Darmstadt ). Stool frequency was evaluated by the volunteers, recording the time and number of stools. Mouth to caecum transit time was estimated using salazosulfapyridine
(SASP) as the test compound [4], measuring SP in saliva by a specific and selective HPLC method [5]. Means and SDs of the parameters were
calculated and tested by analysis of variance (ANOVA, randomized
factorial design) for differences. 95% confidence intervals were calculated for cumulative urinary magnesium excretion. For statistical analysis of stool frequency, the one criterion variance analysis of Kruskal and Wallis was applied [6]. During the higher magnesium dosage, stool frequency was increased 1.8-fold by magnesium-oxide, 3.2-fold by granules and 2.0-fold by tablets of magnesium-L-aspartate-HCI. The differences between the treatment groups did not reach statistical significance. Mean mouth-caecum transit time of about 4 h was not affected by magnesium treatment, suggesting that the magnesium preparations exerted their laxative effect mainly in the colon. Minor adverse effects were reported in each group, such as flatulence. diarrhoea, and gastric discomfort. There were complaints of an unpleasant taste of the granule formulation, which may influence patients compliance. Urine pH was decreased ( - 0.5) during magnesiumL-aspart ate-HCl and increased ( + 0.5) during magnesium-oxide (P < 0.01) administration, indicating a slight disturbance of the acid/base equilibrium. This aspect may be of clinical importance, particularly in elderly patients with multiple diseases. Calcium and potassium levels in plasma and urine were not altered by magnesium treatment. Plasma magnesium, remained unchanged too. The mean cumulative urinary magensium excretion was similar during the placebo and control periods, ranging from 77.5 to 93 .7 mEq/week. There was a significant increase during magnesium administra tion,more marked during the Mg-L-asparta te-HCl phase (P < 0.0001). The maximum value of 187.4 mEq/week was reached during treatment with magnesium-L-asparateHCI granules 90 mEq/d. The differences between the three treatment groups indicated better absorption of magnesium-L-asparate-HCI than of magnesium-oxide. One possible explanation might be the poor solubility of magnesium-oxide, which in water is 8.6 mg/di [7].
In conclusion, all three formulations of magnesium given in the trial were well tolerated, but they increased the number of stools. Magnesium-oxide showed significantly lower absorption than magnesium L-asparate-HCI.
As there were complaints of an unpleasant taste of the resuspended
granules, tablets of magnesium-L-aspartateHCI appear to be the first choice for magnesium substitution among the formulations investigated.
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Magnesium deficiency is seen with some frequency in the outpatient setting and requires oral repletion or maintenance therapy. The purpose of this study was to measure the bioavailability of four commercially-available preparations of magnesium, and to test the claim that organic salts are more easily absorbed. Bioavailability was measured as the increment of urinary maginesium excretion in normal volunteers given approximately 21 mEq/day of the test preparations. Results indicated relatively poor bioavailability of magnesium oxide (fractional absorption 4 per cent) but significantly higher and equivalent bioavailability of magnesium chloride, magnesium lactate and magnesium aspartate. We conclude that there is relatively poor bioavailability of magnesium oxide, but greater and equivalent bioavailability of magnesium chloride, lactate, and aspartate. Inorganic magnesium salts, depending on the preparation, may have bioavailability equivalent to organic magnesium salts.
Magnesium is an important cofactor for many biological processes, such as protein synthesis, nucleic acid stability, or neuromuscular excitability. Extracellular magnesium concentration is tightly regulated by the extent of intestinal absorption and renal excretion. Despite the critical role of magnesium handling, the exact mechanisms mediating transepithelial transport remained obscure. In the past few years, the genetic disclosure of inborn errors of magnesium handling revealed several new proteins along with already known molecules unexpectedly involved in renal epithelial magnesium transport, e.g., paracellin-1, a key player in paracellular magnesium and calcium reabsorption in the thick ascending limb or the gamma-subunit of the Na(+)-K(+)-ATPase in the distal convoluted tubule. In this review, we focus on TRPM6, an ion channel of the "transient receptor potential (TRP) gene family, which, when mutated, causes a combined defect of intestinal magnesium absorption and renal magnesium conservation as observed in primary hypomagnesemia with secondary hypocalcemia.
To investigate the long-term effect of oral magnesium supplementation on clinical symptoms, bronchial reactivity, lung function and allergen-induced skin responses in children and adolescents with moderate persistent asthma.
A double-blind randomized parallel placebo-controlled study.
The patients were recruited from the Pediatric Outpatient Clinic, Division of Pulmonology, Allergy and Immunology, and followed at the Center for Investigation in Pediatrics at State University of Campinas Hospital, Brazil. Thirty-seven out of 72 patients met the study criteria. There were no dropouts.
The 37 patients (aged 7-19 years, 19 males) were randomized in two groups: magnesium (n=18, 300 mg/day) and placebo (n=19), during 2 months. Both patient groups received inhaled fluticasone (250 microg twice a day) and salbutamol as needed. The primary outcome was bronchial reactivity evaluated with methacholine challenge test (PC20).
After a follow-up of 2 months, the methacholine PC20 for testing bronchial reactivity has augmented significantly in the magnesium group only. The skin responses to recognized antigens have also decreased in patients treated with magnesium. The forced vital capacity (FVC), the forced expiratory volume at first second (FEV1), the forced expiratory flow at 25-75 and the FEV1/FVC ratio were similar in both groups. The magnesium group presented fewer asthma exacerbations and used less salbutamol compared to the placebo group.
Oral magnesium supplementation helped to reduce bronchial reactivity to methacholine, to diminish their allergen-induced skin responses and to provide better symptom control in pediatric patients with moderate persistent asthma treated with inhaled fluticasone.
Background:
Aim of this study was to evaluate adjuvant magnesium orotate on mortality and clinical symptoms in patients with severe heart failure under optimal cardiovascular medication.
Methods:
In a monocentric, controlled, double-blind study, 79 patients with severe congestive heart failure (NYHA IV) under optimal medical cardiovascular treatment were randomised to receive either magnesium orotate (6000 mg for 1 month, 3000 mg for about 11 months, n=40) or placebo (n=39). Both groups were comparable in demographic data, duration of heart failure and pre- and concomitant treatment.
Results:
After mean treatment duration of 1 year (magnesium orotate: 364.1+/-14.7 days, placebo: 361.2+/-12.7 days) the survival rate was 75.7% compared to 51.6% under placebo (p<0.05). Clinical symptoms improved in 38.5% of patients under magnesium orotate, whereas they deteriorated in 56.3% of patients under placebo (p<0.001).
Conclusion:
Magnesium orotate may be used as adjuvant therapy in patients on optimal treatment for severe congestive heart failure, increasing survival rate and improving clinical symptoms and patient's quality of life.
Aim of this study was to evaluate adjuvant magnesium orotate on mortality and clinical symptoms in patients with severe heart failure under optimal cardiovascular medication.
In a monocentric, controlled, double-blind study, 79 patients with severe congestive heart failure (NYHA IV) under optimal medical cardiovascular treatment were randomised to receive either magnesium orotate (6000 mg for 1 month, 3000 mg for about 11 months, n = 40) or placebo (n = 39). Both groups were comparable in demographic data, duration of heart failure and pre- and concomitant treatment.
After mean treatment duration of 1 year (magnesium orotate: 364.1 +/- 14.7 days, placebo: 361.2 +/- 12.7 days) the survival rate was 75.7% compared to 51.6% under placebo (p < 0.05). Clinical symptoms improved in 38.5% of patients under magnesium orotate, whereas they deteriorated in 56.3% of patients under placebo (p < 0.001).
Magnesium orotate may be used as adjuvant therapy in patients on optimal treatment for severe congestive heart failure, increasing survival rate and improving clinical symptoms and patient's quality of life.
Magnesium absorption has been studied in both humans and animals under diverse experimental conditions. As a result, the data often appear confusing and conflicting. In this review we attempt to summarize information concerning Mg absorption and, where possible, to reconcile apparently conflicting observations. Most studies suggest that Mg is absorbed predominantly in the distal intestine. At usual Mg intakes, Mg absorption occurs primarily by intercellular diffusional and solvent drag mechanisms. There is evidence for a saturable component of Mg absorption in the small intestine and the descending colon that is important at low dietary Mg intakes. Pharmacological doses of vitamin D increase Mg absorption in both vitamin D-deficient and vitamin D-replete animals. A substantial amount of Mg absorption, however, occurs independent of vitamin D. In addition, vitamin D may reduce Mg retention through increases in urinary Mg excretion. Intestinal interactions between Mg and calcium or phosphate have been demonstrated in both humans and animals. The nature of these interactions cannot be readily explained by data currently available.
This study compared magnesium oxide and magnesium citrate with respect to in vitro solubility and in vivo gastrointestinal absorbability. The solubility of 25 mmol magnesium citrate and magnesium oxide was examined in vitro in solutions containing varying amounts of hydrochloric acid (0-24.2 mEq) in 300 ml distilled water intended to mimic achlorhydric to peak acid secretory states. Magnesium oxide was virtually insoluble in water and only 43% soluble in simulated peak acid secretion (24.2 mEq hydrochloric acid/300 ml). Magnesium citrate had high solubility even in water (55%) and was substantially more soluble than magnesium oxide in all states of acid secretion. Reprecipitation of magnesium citrate and magnesium oxide did not occur when the filtrates from the solubility studies were titrated to pH 6 and 7 to stimulate pancreatic bicarbonate secretion. Approximately 65% of magnesium citrate was complexed as soluble magnesium citrate, whereas magnesium complexation was not present in the magnesium oxide system. Magnesium absorption from the two magnesium salts was measured in vivo in normal volunteers by assessing the rise in urinary magnesium following oral magnesium load. The increment in urinary magnesium following magnesium citrate load (25 mmol) was significantly higher than that obtained from magnesium oxide load (during 4 hours post-load, 0.22 vs 0.006 mg/mg creatinine, p less than 0.05; during second 2 hours post-load, 0.035 vs 0.008 mg/mg creatinine, p less than 0.05). Thus, magnesium citrate was more soluble and bioavailable than magnesium oxide.
In view of the widespread use of magnesium (Mg) as a nutritional supplement, we investigated whether Mg would affect the absorption of calcium (Ca) as the intestinal absorption sites for Mg and Ca differ.
The intestinal absorption of Ca, using 47CaCl2 as the tracer, and metabolic balances of Ca, phosphorus (P) and Mg were determined in five adult males under strictly controlled dietary conditions in control studies and during Mg supplementation. Mg was given as magnesium oxide (MgO) in 10 studies during two Ca intakes: five studies during a low Ca intake of 241 mg/day and five studies during a normal Ca intake of 812 mg/day. Dietary Mg intake ranged from 241 to 264 mg/day in control studies. During Mg supplementation, the total Mg intake ranged from 789 to 826 mg/day.
There was no change of the intestinal Ca absorption during Mg supplementation during the two Ca intakes. The only change was the higher 1-hour 47Ca plasma level in the 47Ca absorption studies during the high Mg intake. Urinary Ca increased during Mg supplementation only during the low Ca intake, the Ca balance became more negative but this difference was not significant. There was also no change in Ca excretion or Ca balance during the high Mg intake at the normal Ca intake of 800 mg/day. P balance studies showed a slight decrease in urinary P and an increase in fecal P, but the P balances did not change. Mg balances were negative in control studies during the two Ca intakes. Supplemental Mg increased both urinary and fecal Mg excretion and the Mg balance became positive, but these differences were not significant.
The increased Mg intake of 826 mg did not affect intestinal Ca absorption determined with tracer doses of 47Ca during Ca intakes of 241 and 812 mg/day.
In a double-blind controlled trial, 91 middle-aged and elderly women with mild to moderate hypertension who were not on antihypertensive medication were randomly assigned to treatment with magnesium aspartate-HCl (20 mmol Mg/d) or placebo for 6 mo. Magnesium aspartate-HCl in the given dose was well-tolerated and was not associated with an increased frequency of diarrhea compared with placebo. At the end of the study, systolic blood pressure had fallen by 2.7 mm Hg (95% CI -1.2, 6.7; P = 0.18) and diastolic blood pressure by 3.4 mm Hg (1.3, 5.6; P = 0.003) more in the magnesium group than in the placebo group. Blood pressure response was not associated with baseline magnesium status, as measured by dietary magnesium intake and urinary magnesium excretion. Urinary magnesium excretion in the magnesium group increased by 50% during the intervention period. No changes were seen in other biochemical indexes, including serum concentrations of total and high-density-lipoprotein cholesterol. The findings suggest that oral supplementation with magnesium aspartate-HCl may lower blood pressure in subjects with mild to moderate hypertension.
Since magnesium regulates calcium transport, and magnesium replacement in magnesium-deficient postmenopausal patients resulted in unexpected improvement in documented osteoporosis, we investigated the effect of magnesium treatment on trabecular bone density in postmenopausal osteoporosis. Thirty-one postmenopausal patients (mean age +/- SD = 57.6 +/- 10.6 years), consecutively admitted to the Back Rehabilitation Unit with musculoskeletal pain of non-malignant origin and bone density values of < or = 1.19 g/cm3 (measured by Compton Bone Densitometer), received two to six tablets daily of 125 mg each of magnesium hydroxide (Magnesium Magma USP/; 'Mazor', Israel) for 6 months and two tablets for another 18 months in a 2 year, open, controlled therapeutic trial. Twenty-three symptom-free postmenopausal women (mean +/- SD = 61.2 +/- 6.2 years) whose bone density was concurrently assessed at the same laboratory and who were found to have osteoporosis but refused treatment, served as controls. No new fractures occurred. Twenty-two patients (71 per cent) responded by a 1-8 per cent rise of bone density. The mean bone density of all treated patients increased significantly after 1 year (P < 0.02) and remained unchanged after 2 years (P > 0.05). The mean bone density of the responders increased significantly both after one year (P < 0.001) and after 2 years (P < 0.02), while in untreated controls, the mean bone density decreased significantly (P < 0.001). The disparity between the initial mean bone density and bone density after one year in all osteoporotic patients and in the responders differed significantly from that of the controls (both P < 0.001).(ABSTRACT TRUNCATED AT 250 WORDS)
In order to evaluate the prophylactic effect of oral magnesium, 81 patients aged 18-65 years with migraine according to the International Headache Society (IHS) criteria (mean attack frequency 3.6 per month) were examined. After a prospective baseline period of 4 weeks they received oral 600 mg (24 mmol) magnesium (trimagnesium dicitrate) daily for 12 weeks or placebo. In weeks 9-12 the attack frequency was reduced by 41.6% in the magnesium group and by 15.8% in the placebo group compared to the baseline (p < 0.05). The number of days with migraine and the drug consumption for symptomatic treatment per patient also decreased significantly in the magnesium group. Duration and intensity of the attacks and the drug consumption per attack also tended to decrease compared to placebo but failed to be significant. Adverse events were diarrhea (18.6%) and gastric irritation (4.7%). High-dose oral magnesium appears to be effective in migraine prophylaxis.
To determine whether oral magnesium supplementation (as magnesium chloride [MgCl(2)] solution) improves both insulin sensitivity and metabolic control in type 2 diabetic subjects with decreased serum magnesium levels.
This study was a clinical randomized double-blind placebo-controlled trial. A total of 63 subjects with type 2 diabetes and decreased serum magnesium (serum magnesium levels </=0.74 mmol/l) treated by glibenclamide received either 50 ml MgCl(2) solution (containing 50 g MgCl(2) per 1,000 ml solution) or placebo daily for 16 weeks. Chronic diarrhea, alcoholism, use of diuretic and/or calcium antagonist drugs, and reduced renal function were exclusion criteria. Homeostasis model assessment for insulin resistance (HOMA-IR) was used as the parameter of insulin sensitivity and glucose and HbA(1c) as parameters of metabolic control.
At the end of the study, subjects who received magnesium supplementation showed significant higher serum magnesium concentration (0.74 +/- 0.10 vs. 0.65 +/- 0.07 mmol/l, P = 0.02) and lower HOMA-IR index (3.8 +/- 1.1 vs. 5.0 +/- 1.3, P = 0.005), fasting glucose levels (8.0 +/- 2.4 vs. 10.3 +/- 2.1 mmol/l, P = 0.01), and HbA(1c) (8.0 +/- 2.4 vs. 10.1 +/- 3.3%, P = 0.04) than control subjects.
Oral supplementation with MgCl(2) solution restores serum magnesium levels, improving insulin sensitivity and metabolic control in type 2 diabetic patients with decreased serum magnesium levels.
Published data on the bioavailability of various Mg preparations is too fragmented and scanty to inform proper choice of Mg preparation for clinical studies. In this study, the relative bioavailability of three preparations of Mg (amino-acid chelate, citrate and oxide) were compared at a daily dose of 300 mg of elemental Mg in 46 healthy individuals. The study was a randomised, double-blind, placebo-controlled, parallel intervention, of 60 days duration. Urine, blood and saliva samples were taken at baseline, 24 h after the first Mg supplement was taken ('acute' supplementation) and after 60 days of daily Mg consumption ('chronic' supplementation). Results showed that supplementation of the organic forms of Mg (citrate and amino-acid chelate) showed greater absorption (P = 0.033) at 60 days than MgO, as assessed by the 24-h urinary Mg excretion. Mg citrate led to the greatest mean serum Mg concentration compared with other treatments following both acute (P = 0.026) and chronic (P = 0.006) supplementation. Furthermore, although mean erythrocyte Mg concentration showed no differences among groups, chronic Mg citrate supplementation resulted in the greatest (P = 0.027) mean salivary Mg concentration compared with all other treatments. Mg oxide supplementation resulted in no differences compared to placebo. We conclude that a daily supplementation with Mg citrate shows superior bioavailability after 60 days of treatment when compared with other treatments studied.
Although hypomagnesemia reduces insulin sensitivity, benefits of magnesium supplementation to non-diabetic insulin resistant subjects has not been established. Our purpose was to determine whether oral magnesium supplementation with magnesium chloride (MgCl2) 2.5 g daily modify insulin sensitivity in non-diabetic subjects.
This study was a 3 months randomized double-blind placebo-controlled trial. Apparently healthy subjects were eligible to participate if they had insulin resistance (HOMA-IR index equal or greater than 3.0) and hypomagnesemia (Serum magnesium levels equal or lower than 0.74 mmol/l). Subjects were randomized to receive either, MgCl2 2.5 g daily or placebo by 3-months.
At baseline there were not significant anthropometric or laboratory differences between both groups. At ending of the study, magnesium-supplemented subjects significantly increased their serum magnesium levels (0.61 +/- 0.08 to 0.81 +/- 0.08 mmol/l, p<0.0001) and reduced HOMA-IR index (4.6 +/- 2.8 to 2.6 +/- 1.1, p<0.0001), whereas control subjects did not (0.62 +/- 0.08 to 0.61 +/- 0.08 mmol/l, p=0.063 and 5.2 +/- 1.9 to 5.3 +/- 2.9, p=0.087).
Oral magnesium supplementation improves insulin sensitivity in hypomagnesemic non-diabetic subjects. Clinical implications of this finding have to be established.
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.
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