Blood Magnesium Concentrations Research Articles

Timing of administration of antenatal magnesium sulphate and correlation with umbilical cord blood magnesium levels in preterm babies

BackgroundThe effectiveness of MgSO4 for foetal neuroprotection is acknowledged, but the best time to provide it in relation to birth is a conundrum, and dose schedule is yet unknown. Understanding the determinants of the magnesium levels in cord blood aids in determining the appropriate timing and length of administration. Aim and objectiveTo assess the cord blood magnesium concentration in relation to the timing of MgSO4 and delivery. To achieve ROC in relation to optimum level of cord blood magnesium concentration in relation to neonatal outcome variables. Study designA prospective observational study conducted in a tertiary care hospital over 2 years in women having preterm delivery from 26 weeks to 33 + 6 weeks, who received Neuroprophylaxis. Cord blood was collected for magnesium level estimation. Baby followed 24 h after delivery. ROC analysis performed for predicting an optimal cut-off for a continuous predictor predicting binary outcome. Results85 recruited cases divided into bolus group, bolus + infusion group. The mean cord blood magnesium (n = 85) was 3.8 mg/dl. The AUROC for Gestational Age at Administration predicting Baby Outcome: 0.699, It was statistically significant (p = 0.034). The AUROC for Cord Blood Mg predicting Baby Outcome: 0.606, It was not statistically significant (p = 0.262). ConclusionMean cord blood magnesium levels served as a tool to determine the timing and duration of Neuroprophylaxis. Mean cord blood magnesium of 3.8 mg/dl should be achieved to serve the purpose of Neuroprotection. To achieve this, Bolus followed by Infusion should be administered for at-least 6 h prior to delivery.

Effects of dietary nitrogen and/or phosphorus reduction on mineral homeostasis and regulatory mechanisms in young goats.

The reduction of nitrogen (N) and phosphorus (P) in ruminant feed is desirable due to costs and negative environmental impact. Ruminants are able to utilize N and P through endogenous recycling, particularly in times of scarcity. When N and/or P were reduced, changes in mineral homeostasis associated with modulation of renal calcitriol metabolism occurred. The aim of this study was to investigate the potential effects of dietary N- and/or P-reduction on the regulatory mechanisms of mineral transport in the kidney and its hormonal regulation in young goats. During N-reduction, calcium (Ca) and magnesium (Mg) concentrations in blood decreased, accompanied by a lower protein expression of cytochrome P450 family 27 subfamily B member 1 (CYP27B1) (p = 0.016). The P-reduced fed goats had low blood phosphate concentrations with simultaneously high Ca and Mg levels. The insulin-like growth factor 1 concentrations decreased significantly with P-reduction. Furthermore, gene expression of CYP27B1 (p < 0.001) and both gene (p = 0.025) and protein (p = 0.016) expression of the fibroblast growth factor receptor 1c isoform in the kidney were also significantly reduced during a P-reduced diet. ERK1/2 activation exhibited a trend toward reduction in P-reduced animals. Interestingly, calcitriol concentrations remained unaffected by either restriction individually, but interacted significantly with N and P (p = 0.014). Additionally, fibroblast growth factor 23 mRNA expression in bone decreased significantly with P-restriction (p < 0.001). These results shed light on the complex metabolic and regulatory responses of mineral transport of young goats to dietary N and P restriction.

Blood fibroblast growth factor 23 concentration in cats with and without chronic kidney disease: a scoping review.

This study undertook a scoping review of research on blood fibroblast growth factor 23 (FGF-23) concentrations in healthy non-azotemic cats and cats with chronic kidney disease (CKD) to describe the volume and nature of existing literature, to determine whether published studies provide adequate evidence to support the use of FGF-23 as a biomarker in clinical practice and to identify any existing gaps in knowledge. PRISMA Extension for Scoping Reviews guidelines were used to design and perform the scoping review. Online databases were used to identify observational and clinical studies of blood FGF-23 concentrations in healthy cats and cats with CKD published before December 2022. Study and population characteristics and descriptive data on FGF-23 concentrations were extracted. A total of 205 publications were reviewed; 17 were retained for inclusion. Most studies were retrospective. Most studies included cats with International Renal Interest Society stage 2-4 CKD, with some variation. Key concepts explored in the literature include FGF-23 concentrations by CKD stage, effect of dietary phosphate restriction on FGF-23 concentrations, relationship between FGF-23 concentrations and blood phosphorus, calcium and magnesium concentrations, and FGF-23 concentrations in cats with progressive CKD. FGF-23 concentrations tended to be higher in cats with CKD compared with healthy cats, with an overlap between healthy and CKD populations, and there was significant variation within stages of CKD. FGF-23 is a biomarker of interest for the management and monitoring of phosphate overload in cats. Studies support several potential clinical applications for measuring FGF-23 concentration in practice; however, evidence is limited. Research on FGF-23 in cats with CKD would benefit from longitudinal, prospective studies that standardize CKD diagnosis and categorize cats by stage using current guidelines. Studies should include cats with early-stage, non-azotemic CKD and use commercially available assays so such results are comparable across studies.

Inhibition of pannexin-1 does not restore electrolyte balance in precystic Pkd1 knockout mice.

Mutations in PKD1 and PKD2 cause autosomal dominant polycystic kidney disease (ADPKD), which is characterized by the formation of fluid-filled cysts in the kidney. In a subset of ADPKD patients, reduced blood calcium (Ca2+) and magnesium (Mg2+) concentrations are observed. As cystic fluid contains increased ATP concentrations and purinergic signaling reduces electrolyte reabsorption, we hypothesized that inhibiting ATP release could normalize blood Ca2+ and Mg2+ levels in ADPKD. Inducible kidney-specific Pkd1 knockout mice (iKsp-Pkd1-/-) exhibit hypocalcemia and hypomagnesemia in a precystic stage and show increased expression of the ATP-release channel pannexin-1. Therefore, we administered the pannexin-1 inhibitor brilliant blue-FCF (BB-FCF) every other day from Day 3 to 28 post-induction of Pkd1 gene inactivation. On Day 29, both serum Ca2+ and Mg2+ concentrations were reduced in iKsp-Pkd1-/- mice, while urinary Ca2+ and Mg2+ excretion was similar between the genotypes. However, serum and urinary levels of Ca2+ and Mg2+ were unaltered by BB-FCF treatment, regardless of genotype. BB-FCF did significantly decrease gene expression of the ion channels Trpm6 and Trpv5 in both control and iKsp-Pkd1-/- mice. Finally, no renoprotective effects of BB-FCF treatment were observed in iKsp-Pkd1-/- mice. Thus, administration of BB-FCF failed to normalize serum Ca2+ and Mg2+ levels.

Massive Transfusion Increases Serum Magnesium Concentration.

(1) Background: The massive transfusion of packed red blood cells (RBCs) is a lifesaving procedure, but it is associated with complications, e.g., dysmagnesemia. Since magnesium is an intracellular ion, the transfused RBCs can significantly influence the magnesium concentration in the recipient's blood. (2) Methods: A retrospective study was performed among 49 patients hospitalized in the Central Clinical Hospital of the Medical University of Warsaw who received a massive blood transfusion (≥4 units/h). Data on laboratory results and patient history were collected from the hospital database. The intracellular RBCs magnesium concentration was measured in 231 samples using the colorimetric method. (3) Results: There were statistically significant changes in the mean serum magnesium concentration preoperatively and 24 h postoperatively (0.87 ± 0.13 vs. 1.03 ± 0.14, p < 0.00001) and 48 h postoperatively (0.87 ± 0.13 vs. 1.06 ± 0.15, p < 0.00001). Patients who died had significantly higher serum magnesium concentrations (p < 0.05). The median intracellular magnesium concentration in RBCs was 0.91 (0.55-1.8) mmol/L, which is below the reference values of 1.65-2.65 mmol/L. (4) Conclusions: Transfused RBCs significantly increased the serum magnesium concentration 24 h and 48 h postoperatively. It could be a result of mild hemolysis, as the median intracellular magnesium concentration in RBCs was below the reference values.

Effects of genetically determined mineral status on life expectancy: a Mendelian randomization study.

Effects of genetically determined mineral status on life expectancy: a Mendelian randomization study.

The Assessment of Neonatal Anthropometric Indices Association with Umbilical Cord Blood Zinc and Magnesium Levels.

The present research aims to find the association between neonatal anthropometric parameters and zinc and magnesium concentration in cord blood. The current cross-sectional report is a sub-study from the "PERSIAN Birth Cohort Study" conducted on 112 pairs of mother-neonate referring to the index hospitals for giving birth to their children during 2018-19. Umbilical cord blood was collected at delivery for the measurement of zinc and magnesium. Anthropometric indices were measured in standard protocols. Validated questionnaires were used for maternal diet in different trimesters. Dietary patterns were acquired based on exploratory factor analysis. The birth weight was reversely correlated with zinc concentration (r = -0.249, P-value = 0.008); however, the other anthropometric parameters did not show any association with zinc levels (P-value > 0.05). Similar evaluations for magnesium revealed no association between any of the anthropometric indices and this micronutrient agent (P-value > 0.05). Further evaluations represented insignificant differences in both zinc (P-value = 0.51) and magnesium levels (P-value = 0.49) between those with normal versus low birth weight. There was a negative association between the Western dietary pattern in the first trimester of pregnancy and cord blood zinc concentration (β (SE) = -0.21 (0.10); P = 0.026); while healthy and traditional dietary patterns in second and third trimesters were positively related to cord zinc concentration (all P < 0.05). This research did not document a positive statistical association of cord blood zinc and magnesium with birth weight. The association of maternal Western dietary patterns with lower cord blood zinc levels highlights the importance of healthy nutritional habits in pregnancy.

Assessment of Noninferiority of Delayed Oral Calcium Supplementation on Blood Calcium and Magnesium Concentrations and Rumination Behavior in Dairy Cows

We investigated whether delaying oral calcium (Ca) bolus administration to the second day postpartum (DEL) was noninferior to bolus administration within 24 h of calving (CON) in its effects on plasma Ca concentrations during the first five days in milk (DIM). We also investigated the effects of DEL vs. CON strategies on magnesium (Mg) concentrations and daily rumination time (RT). Twenty-three multiparous (parity ≥ 3) dairy cows were randomly assigned to the CON (n = 11) or DEL (n = 12) treatment. Blood Ca and Mg were measured at 1–5 DIM and RT was monitored from −7 d to 7 d relative to calving. The noninferiority margin was a difference in Ca concentration of 0.15 mmol/L. Blood Ca and Mg concentrations and RT were analyzed by multivariable linear mixed models accounting for repeated measures. Blood Ca concentrations were 0.07 mmol/L (95% confidence interval: −0.30–0.17) less in DEL cows than CON cows, thus non-inferiority results were inconclusive. The Ca concentration increased across the first 5 DIM but did not differ between treatments while Mg concentrations decreased in both treatments (p &lt; 0.001). There was no treatment difference in RT (CON: 436 ± 21, DEL: 485 ± 19 min/d). While noninferiority results were inconclusive, similar blood Ca dynamics between CON and DEL treatment strategies indicates that delayed Ca administration is a potential management option for commercial dairy farms; however, additional studies using large sample sizes are warranted to confirm these findings.

Strategy for Calculating Magnesium Sulfate Dose in Obese Patients: A Randomized Blinded Trial.

Magnesium sulfate has analgesic properties during the postoperative period. However, there is a knowledge gap in pharmacology related to the use of the real, ideal, or corrected ideal body weight to calculate its dose in obese patients. This trial compared postoperative analgesia using actual and corrected ideal body weight. Seventy-five obese patients scheduled to undergo laparoscopic gastroplasty or cholecystectomy under general anesthesia were randomly assigned to three groups. The patients in the control group did not receive magnesium sulfate; the other two groups received magnesium sulfate at 40 mg·kg-1 of actual body weight or corrected ideal body weight. In patients with body mass index >30 mg·kg-2 (mean body mass index ranging from 32.964 kg·m-2 to 33.985 kg·m-2, according to the groups) scheduled for video laparoscopic cholecystectomy, there were no differences in the blood magnesium concentrations in the groups receiving magnesium sulfate throughout the study, regardless of whether the strategy to calculate its dose was based on total or corrected ideal body weight. Patients in the groups receiving magnesium sulfate showed a significant reduction in morphine consumption (p ≤ 0.001) and pain scores (p=0.006) in the postoperative period compared to those in the control group. There were no significant differences in morphine consumption (p=0.323) or pain scores (p=0.082) between the two groups receiving magnesium sulfate. There were no differences in the total duration of neuromuscular block induced by cisatracurium among the three groups (p=0.181). Magnesium sulfate decreased postoperative pain and morphine consumption without affecting the recovery time of cisatracurium in obese patients undergoing laparoscopic cholecystectomy. Strategies to calculate the dose based on the actual or corrected ideal body weight had similar outcomes related to analgesia and the resulting blood magnesium concentration. However, as the sample in this trial presented body mass indices ranging from 30.11 kg·m-2 to 47.11 kg/m-2, further studies are needed to confirm these findings in more obese patients, easily found in centers specialized.

Magnesium exposure increases hip fracture risks in patients with chronic kidney disease: a population-based nested case-control study.

Bone fracture is a severe complication in chronic kidney disease (CKD) patients, leading to disability and reduced survival. In CKD patients, blood magnesium (Mg) concentrations are usually above the normal range due to reduced kidney excretion of Mg. The present study examines the association between Mg-containing antacid exposure and the risk of hip fracture of CKD patients. In this nationwide nested case-control study, we enrolled 44,062 CKD patients with hip fracture and 44,062 CKD matched controls, among which the mean age was 77.1years old, and 87.9% was nondialysis CKD. As compared to non-users, Mg-containing antacid users were significantly more likely to experience hip fracture (adjusted odds ratio (OR) 1.36, 95% CI, 1.32 to 1.41; p < 0.001). Subgroup analysis showed that such risk exists in both nondialysis CKD patients and long-term dialysis patients. In contrast, aluminum or calcium-containing-antacid use did not reveal such association. Next, we examined the influence of Mg-containing antacid dosage on hip fracture risk, the adjusted ORs in the first quartile (Q1), Q2, Q3, and Q4 were 1.20 (95% CI, 1.15 to 1.25; p < 0.001), 1.35 (95% CI, 1.30 to 1.41; p < 0.001), 1.49 (95% CI, 1.43 to 1.56; p < 0.001), and 1.54 (95% CI, 1.47 to 1.61; p < 0.001), respectively, showing that such risk exists regardless of the antacid dosage. A receiver operating characteristic curve analysis demonstrated that the best cutoff value of the exposed Mg dose to discriminate the hip fracture is 532mEq during the follow-up period. This population-based study demonstrates a strong link between Mg-containing antacid exposure and the hip fracture risk in both nondialysis CKD and dialysis patients.

Selected Metal Concentration in Maternal and Cord Blood.

Essential and non-essential elements deficiencies may lead to various birth complications. The aim of this paper was to determine calcium (Ca), copper (Cu), iron (Fe), potassium (K), magnesium (Mg), sodium (Na), phosphorus (P), lead (Pb), strontium (Sr), and zinc (Zn) concentrations in maternal blood and cord blood. Whole blood and cord blood samples collected from pregnant women (n = 136) were analyzed for the concentration of the elements by spectrophotometric atomic absorption in inductively coupled argon plasma (ICP-OES). The results showed that Ca, Pb, and Sr concentrations were similar in maternal and cord blood, while Fe and K levels were higher in cord blood than in maternal blood. The cord blood Cu, Na, and Zn concentrations were lower than those in maternal blood, suggesting transplacental transfer of these elements were limited. Moreover, checking the influence of studied elements on the anthropometric parameters of the newborns, we found that the highest number of associations was between Cu in cord blood. Due to the fact that the pregnant women were healthy, and the newborns were without any disorders, we suggest that the values obtained in our study are normal values of studied elements in whole blood and cord blood in patients from Poland.

Diurnal variation of magnesium and the mineral metabolism in patients with chronic kidney disease

Increasing levels of magnesium in blood are associated with reduced risk of cardiovascular disease in chronic kidney disease (CKD). Magnesium supplementation may reduce the progression of vascular calcification in CKD. The diurnal pattern and effect of fasting on magnesium in blood and urine in CKD is unknown, and knowledge of this may influence management of magnesium supplementation.We included ten patients with CKD stage four without diabetes mellitus and ten healthy controls. Participants were admitted to our hospital ward for a 24-h study period. Blood and urine samples were collected in a non-fasting state at 8 o'clock in the morning and every third hour hereafter until the final samples in a fasting state at 8 o'clock the following morning.We found no diurnal variation in plasma magnesium (p = 0.097) in either group, but a significant diurnal variation in urinary excretion of magnesium (p = 0.044) in both CKD and healthy controls with no significant interaction between the two groups, and thus no suggestion that CKD affects diurnal variation of plasma magnesium or urinary magnesium excretion. The levels of plasma magnesium were not significantly different in fasting and non-fasting conditions.Magnesium in plasma does not display a significant diurnal variation and can be measured at any time of day and in both fasting and non-fasting conditions. Urinary magnesium excretion displays diurnal variation, which is likely related to increased uptake of magnesium during meals and helps maintain a stable concentration of magnesium in blood.

High blood iron and magnesium concentrations in broilers fed with different plants in free-range systems

High blood iron and magnesium concentrations in broilers fed with different plants in free-range systems

Incidence, clinical patterns, and risk factors of postpartum uterine diseases in dairy cows from high-altitude tropical herds

The cow's uterus sustains bacterial contamination and active inflammation after calving as part of the normal physiological process of uterine involution. Although the definition, incidence, and risk factors for postpartum uterine diseases (PUD) have been documented in annual calving systems with high-producing cows on total mixed ration, the literature contains little information for other production systems. The objective of this study was to quantify the incidence risk and factors associated with metritis, clinical endometritis, and cytological endometritis in high-altitude tropical dairy herds in a pasture-based system. A total of 248 cows from 5 commercial dairy herds in northern Antioquia, Colombia, were enrolled in this prospective observational longitudinal cohort study. Data collection and PUD diagnosis were performed at d 0, 3, 10, 17, 24, 31, 38, 45, and 52 (±1) after parturition. Between 60 and 70 d, cows were systematically enrolled in a synchronization protocol, and herds were visited monthly for pregnancy diagnosis until 180 ±15 d. The multivariable logistic regression model of variables associated with PUD occurrence included (a) parity, season of calving, transition diet, and body condition score at calving; (b) blood calcium, phosphorus, and magnesium concentrations, and milk urea nitrogen, β-hydroxybutyrate and fat-to-protein ratio; and (c) dystocia, retained placenta, and delayed uterine involution. The incidences of puerperal metritis, clinical metritis (MET), clinical endometritis (CE), and cytological endometritis (CYTO) were 2.8, 25, 29, and 26%, respectively. Retained placenta and dystocia were associated with MET, and MET was associated with CE. Low blood calcium concentration at calving was associated with CYTO. Overall, 51.2% of the cows suffered at least 1 category of PUD during the first 60 d postpartum (DPP). However, cows also suffered from different consecutive clinical events of PUD (MET, CE, and CYTO) during the follow-up period (0 to 180 ±15 DPP). These events could be grouped into 4 types (which were referred to as "clinical patterns") based on interactions between MET, CE, and CYTO.

Manipulating Phosphorus, Calcium, and Magnesium Utilization by Growing Lambs Using Natural Zeolite (Clinoptilolite)

A total of 24 three-month-old lambs with an average weight of 23 ± 1.5 kg were used in this study and fed a complete diet supplemented with natural zeolite at 1% and 2% of feed weight to evaluate the effect of zeolite on calcium (Ca), phosphorus (P), and magnesium (Mg) concentration in tissues (kidney, liver, and muscle), rumen fluid, and blood. Adding zeolite at 2% to the diet resulted in an increase (p &lt; 0.05) in body weight but a depressed feed conversion ratio. Phosphorus digestibility was significantly (p &lt; 0.05) increased with the addition of zeolite while the digestibility of Ca and Mg remained unaffected (p &gt; 0.05). The concentration of Ca, Mg, and P in the liver remained unchanged (p &gt; 0.05) with the addition of zeolite. The addition of zeolite led to a decrease (p &lt; 0.05) in the Ca concentration in the kidney and muscle, whereas the Ca concentration in lambs receiving diets supplemented with 2% zeolite (123.13 and 48.49 µg/g) was significantly (p &lt; 0.05) higher than supplementation at 1% (120.13 and 45.66 µg/g, respectively, for kidney and muscle). Furthermore, serum and rumen fluid concentrations of P, Ca, and Mg exhibited no significant differences upon the addition of zeolite to the diet. Conclusively, diet supplementation by zeolite at 2% improves performance and especially P digestibility, which may result in the reduction in minerals in lambs’ waste and consequently a reduction in environmental pollution.

Magnesium to prevent kidney disease-associated vascular calcification: crystal clear?

Vascular calcification is a prognostic marker for cardiovascular mortality in chronic kidney disease (CKD) patients. In these patients, magnesium balance is disturbed, mainly due to limited ultrafiltration of this mineral, changes in dietary intake and the use of diuretics. Observational studies in dialysis patients report that a higher blood magnesium concentration is associated with reduced risk to develop vascular calcification. Magnesium prevents osteogenic vascular smooth muscle cell transdifferentiation in in vitro and in vivo models. In addition, recent studies show that magnesium prevents calciprotein particle maturation, which may be the mechanism underlying the anti-calcification properties of magnesium. Magnesium is an essential protective factor in the calcification milieu, which helps to restore the mineral-buffering system that is overwhelmed by phosphate in CKD patients. The recognition that magnesium is a modifier of calciprotein particle maturation and mineralization of the extracellular matrix renders it a promising novel clinical tool to treat vascular calcification in CKD. Consequently, the optimal serum magnesium concentration for patients with CKD may be higher than in the general population.

The effect of hemodialysis on serum magnesium concentration in hemodialysis patients.

In recent years, the concentration of magnesium in dialysis patients has drawn an increasing amount of attention. Both hemodialysis and peritoneal dialysis may affect magnesium metabolism, but studies in this area are very limited. This study aimed to investigate the serum magnesium concentrations in hemodialysis patients and examine the factors related to the serum magnesium concentration, and to explore the effect of hemodialysis with conventional hemodialysis solution (magnesium ion concentration 0.5 mmol/L) on blood magnesium concentration. In this single-center, retrospective study, linear regression models were established to explore the factors related to serum magnesium concentration in hemodialysis patients. Serum magnesium concentration was also compared before and after hemodialysis treatment. The data of 148 hemodialysis patients were collected and analyzed. The mean value of pre-hemodialysis total serum magnesium concentration was 1.11±0.14 mmol/L. The prevalence of hypermagnesemia was 73.65%, and 2 patients had hypomagnesemia (1.35%). Data analysis indicated that total platelet count, serum phosphorus level, serum creatinine, plasma albumin, and total serum cholesterol level were significantly related to serum magnesium concentration. After hemodialysis treatment, the serum magnesium concentration was significantly lower when conventional hemodialysis was used. After hemodialysis, the average decrease in the serum magnesium concentration was 0.14 mmol/L. Most patients who received hemodialysis had mild hypermagnesemia when routine dialysate was supplied. Serum magnesium concentration is related to patients' nutritional status. Hemodialysis treatment can decrease the total serum magnesium concentration.

Junctional Ectopic Tachycardia after Complete Repair of Tetralogy of Fallot in Children less than 1 Year

Junctional ectopic tachycardia (JET) is frequent acceleration of rhythm after complete repair of Tetralogy of Fallot. JET is associated with prolongation of been in the ICU and worsening of the prognosis. The present ways of preventing of JET cannot be routinely applied for all patients, so it needs to identify patients with high risk of JET emergence.&#x0D; Purpose. It needs to analyze cases of JET and identify risk factors for patients requiring Tetralogy of Fallot complete repair.&#x0D; Methods and materials. It was analyzed 81 patients with Tetralogy of Fallot after complete repair from 2014 until 2019 in National Amosov Institute of Cardiovascular Surgery.&#x0D; Results and discussion. Post-operative analysis shows that magnesium and potassium levels in blood were lower in patients with JET than in patients without JET (0.9 ± 0.41 and 1.14 ± 0.43, respectively, p &lt; 0.05). Patients with JET were younger (7.8 ± 1.4 and 9.9 ± 1.6, respectively, p &lt; 0.05), had lower body weight (8.1 ± 1.0 and 9.3 ± 0.9, respectively, p &lt; 0.05) and higher heart rate in the pre-operative period (147.6 ± 11.4 and 124.9 ± 13.9, respectively, p &lt; 0.05). It was found out that pre-operative respiratory cyanotic attacks are independent risk factors for JET. During the work we also found that the administration of beta-blockers in the pre-operative period significantly reduces the JET development (4 (26.6%) and 27 (40.9%) respectively, p &lt;0.05).&#x0D; Conclusion.Younger age, lower body weight, and respiratory cyanotic attacks in the pre-operative period are unadjusted risk factors of the JET development in the early postoperative period. Blood magnesium and potassium concentrations are correlated factors in the JET development. Beta-blockers may be recommended for the prevention of JET in the early post-operative period in patients who have risk factors.

Predicting and Testing Bioavailability of Magnesium Supplements.

Despite the presumption of the beneficial effects of magnesium supplementation, little is known about the pharmacokinetics of different magnesium formulations. We aimed to investigate the value of two in vitro approaches to predict bioavailability of magnesium and to validate this in subsequent in vivo testing. In vitro assessment of 15 commercially available magnesium formulations was performed by means of a Simulator of the Human Intestinal Microbial Ecosystem (SHIME®) and by dissolution tests. Two magnesium formulations with contrasting bioavailability prediction from both in vitro tests (best vs. worst) were selected for in vivo testing in 30 subjects. In vivo bioavailability was compared following one acute ingestion by monitoring blood magnesium concentrations up to 6 h following intake. The in vitro tests showed a very wide variation in absorption and dissolution of the 15 magnesium products. In the in vivo testing, a significant different serum magnesium absorption profile was found up to 4 h following supplement ingestion for the two supplements with opposing in vitro test results. Moreover, maximal serum magnesium increase and total area under the curve were significantly different for both supplements (+6.2% vs. +4.6% and 6.87 vs. 0.31 mM.min, respectively). Collectively, poor bioaccessibility and bioavailability in the SHIME model clearly translated into poor dissolution and poor bioavailability in vivo. This provides a valid methodology for the prediction of in vivo bioavailability and effectiveness of micronutrients by specific in vitro approaches.

Ionized and Total Magnesium Levels Change during Repeated Exercise in Older Adults.

Magnesium is essential for health and performance. Sub-optimal levels have been reported for older persons. In addition, physical exercise is known to temporally decrease magnesium blood concentrations. To investigate these observations in conjunction we assessed total (tMg) and ionized magnesium (iMg) concentrations in plasma and whole blood, respectively, during 4 consecutive days of exercise in very old vital adults. 68 participants (age 83.7±1.9 years) were monitored on 4 consecutive days at which they walked 30-40km (average ~8 hours) per day at a self-determined pace. Blood samples were collected one or two days prior to the start of exercise (baseline) and every walking day immediately post-exercise. Samples were analysed for tMg and iMg levels. Baseline tMg and iMg levels were 0.85±0.07 and 0.47±0.07 mmol/L, respectively. iMg decreased after the first walking day (-0.10±0.09 mmol/L, p<.001), increased after the second (+0.11±0.07 mmol/L, p<.001), was unchanged after the third and decreased on the final walking day, all compared to the previous day. tMg was only higher after the third walking day compared to the second walking day (p=.012). In 88% of the participants, iMg levels reached values considered to be sub-optimal at day 1, in 16% of the participants values were sub-optimal for tMg at day 2. Prolonged moderate intensity exercise caused acute effects on iMg levels in a degree comparable to that after a bout of intensive exercise. These effects were not associated with drop-out or health problems. After the second consecutive day of exercise, levels were returned to baseline values, suggesting rapid adaptation/resilience in this population.