Gender-specific correlation of platelet ionized magnesium and serum low-density-lipoprotein cholesterol concentrations in apparently healthy subjects

Systematic Review and Meta-Analysis to Estimate a Reference Range for Circulating Ionized Magnesium Concentrations in Adult Populations

BACKGROUND

There is a lack of consensus on a reference range for ionized magnesium (iMg2+) in blood as a measure of the status of circulating iMg2+ for the screening of populations.

OBJECTIVES

We estimated the reference range of iMg2+ levels for healthy adult populations and the ranges for populations with cardiovascular disease (CVD), type 2 diabetes, hypertension, and renal disease. We also estimated 95% ranges for circulating magnesium (Mg) in healthy and those with cardiometabolic diseases.

METHODS

We searched Ovid MEDLINE, Cochrane Central Register of Controlled Trials, and Embase through 24 July, 2020 to identify articles. We included English, peer-reviewed, randomized controlled trials, prospective and retrospective cohort studies, case-control studies, and cross-sectional studies that measured iMg2+ in blood or circulating Mg at baseline. The protocol was registered on PROSPERO (CRD42020216100). Estimated ranges were calculated by employing a frequentist random-effects model using extracted (or calculated) means and SDs from each included study. We determined the 95% confidence interval of the pooled mean.

RESULTS

A total of 95 articles were included with 53 studies having data for healthy participants and 42 studies having data for participants with cardiometabolic diseases. The estimated reference range for iMg2+ for healthy populations was 0.40-0.68 mmol/L, 0.38-0.64 mmol/L for CVD, 0.34-0.66 mmol/L for type 2 diabetes, 0.39-1.04 mmol/L for hypertension, and 0.40-0.76 mmol/L for renal disease. For circulating Mg, the estimated range was 0.72-1.0 mmol/L for healthy adults, 0.56-1.05 mmol/L for CVD, 0.58-1.14 mmol/L for type 2 diabetes, 0.60-1.08 mmol/L for hypertension, and 0.59-1.26 mmol/L for renal disease.

CONCLUSIONS

Estimated reference ranges for cardiometabolic disease states for both iMg2+ and circulating Mg were broad and overlapped with the estimated range for healthy populations (0.40-0.68 mmol/L). Further studies should evaluate whether iMg2+ can be used as a biomarker of cardiometabolic disease.

Does magnesium have a role in the treatment of patients with coronary artery disease?

Hypomagnesemia is common in hospitalized patients, especially in elderly patients with coronary artery disease (CAD) and/or those with chronic heart failure. Hypomagnesemia is associated with increased all cause mortality and mortality from CAD. Magnesium supplementation improves myocardial metabolism, inhibits calcium accumulation and myocardial cell death; it improves vascular tone, peripheral vascular resistance, afterload and cardiac output, reduces cardiac arrhythmias and improves lipid metabolism. Magnesium also reduces vulnerability to oxygen-derived free radicals, improves endothelial function and inhibits platelet function, including platelet aggregation and adhesion, which potentially confers upon magnesium physiologic and natural effects similar to adenosine-diphosphate inhibitors such as clopidogrel. However, data regarding the use of magnesium in patients with acute myocardial infarction (AMI) are conflicting. Although some previous relatively small randomized clinical trials demonstrated a remarkable reduction in mortality when intravenous magnesium was administered to relatively high risk AMI patients, two recently published large-scale randomized clinical trials (the Fourth International Study of Infarct Survival [ISIS 4] and Magnesium in Coronaries [MAGIC]) were unable to demonstrate any advantage of intravenous magnesium over placebo. Nevertheless, the theoretical benefits of magnesium supplementation as a cardio-protective agent in CAD patients, promising results from animal and human studies, its relatively low-cost and ease of handling requiring no special expertise, together with its excellent tolerability, gives magnesium a place in treating CAD patients, especially in those at high risk, such as CAD patients with heart failure, the elderly and hospitalized patients with hypomagnesemia. Furthermore, magnesium therapy is indicated in life-threatening ventricular arrhythmias such as torsades de pointes and intractable ventricular tachycardia.

Erythrocyte magnesium concentration as an index of magnesium status: a perspective from a magnesium supplementation study

We investigated the utility of erythrocyte magnesium concentrations as an index of magnesium status. Calculated from the analytical and biological variation, the critical difference, i.e. the difference between results from serial specimens before they can be said to be statistically different, was 22.4% (P<0.05). Magnesium supplementation of 250 mg/day for 3 weeks in 20 women with an erythrocyte magnesium concentration less than the 15th percentile of a population sample (n=219), resulted in an increase in erythrocyte magnesium concentration of only 1.6%. We therefore conclude that sequential erythrocyte magnesium measurements are not useful for the monitoring of individual changes in magnesium intake and status.

Gender differences in basal protein kinetics in young adults

Gender affects energy expenditure and influences the relative utilization of carbohydrate and fat as fuels. However, little is known about the possible effects of gender on protein metabolism. Thus, we compared whole body and plasma (albumin and fibrinogen) protein kinetics in the basal postabsorptive state in young, untrained volunteers divided into two groups according to gender (women: n=17; age, 24+/-4 yr; men: n=17; age, 25+/-2 yr). The two groups were matched for body mass index. Protein kinetics were measured by means of L-[1-14C]leucine infusion. The leucine whole body rate of appearance, an index of proteolysis, and nonoxidative rate of disappearance, an index of protein synthesis, were similar in the two groups. However, the leucine oxidation rate was significantly lower in women compared to men (0.23+/-0.07 vs. 0.31+/-0.08 micromol/kg min; P=0.0062). Similar results were obtained when data were adjusted for estimated body composition. Albumin and fibrinogen fractional secretion rates were not different in the two groups. In conclusion, in the basal state leucine oxidation is lower in women than in men regardless of body composition. This could be one of the factors contributing to the lower metabolic rate in women.