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.

Relationship between short-term self-reported dietary magnesium intake and whole blood ionized magnesium (iMg2+) or serum magnesium (s-Mg) concentrations.

OBJECTIVE: Since we and others have shown that supplemental magnesium raises whole blood ionized magnesium (iMg2+) we investigated the relationships between self-reported dietary magnesium intake and concentrations of whole blood iMg2+ and serum magnesium (s-Mg). METHODS: We obtained whole blood iMg2+ concentrations, as well as s-Mg concentrations, from a pilot, three-arm, randomized, controlled, crossover bioavailability study of magnesium supplements (n = 23; 105 measures). Dietary magnesium intake was assessed using three-day food records and the Nutrition Data System for Research (NDSR, University of Minnesota, MN, USA). Whole blood iMg2+ was measured with an electrode analyser (NOVA Biochemical, Waltham, MA, USA), whereas s-Mg was measured using atomic absorption spectroscopy. A linear mixed-effects model was employed with dietary magnesium as the outcome variable and iMg2+, s-Mg, study treatment and study visit as fixed effects. We adjusted age, gender, race and body mass index covariates. RESULTS: Values for dietary magnesium, iMg2+ and s-Mg were 303.8 ± 118.9 mg/day, 1.3 ± 0.1 mg/dL and 2.2 ± 4.1 mg/dL, respectively. No association was found between dietary magnesium intake and iMg2+ -125 ± 176.95 (p = .49) or s-Mg -9.33 ± 5.04 (p = .08). CONCLUSIONS: Whole blood iMg2+ and s-Mg concentrations do not reflect short-term self-reported dietary intake in adults. Further research is needed to determine whether blood biomarkers of magnesium may reflect dietary magnesium intake.Key messagesDietary intake of magnesium, a shortfall nutrient, may be objectively measured using blood biomarkers of magnesium.Serum magnesium and whole blood iMg2+ were not associated with short-term dietary intake of magnesium.

Racial and Ethnic Differences in Eating Duration and Meal Timing: Findings from NHANES 2011-2018.

Background: In addition to quantity and quality, meal timing and eating duration are additional dietary characteristics that impact cardiometabolic health. Given that cardiometabolic health disparities exist among racial and ethnic groups, we examined whether meal timing and eating duration are additional diet-related differences among racial and ethnic groups. Methods: Participants (n = 13,084) were adults (≥20 years) from the National Health and Nutrition Examination (NHANES, 2011−2018) Survey. Times of first and last meal and the interval between them (eating duration) were derived from two 24-h dietary recalls. Multiple linear regression analyses compared these variables among race and ethnicity after adjusting for potential confounders. Results: Compared to non-Hispanic White adults, the first mealtime was significantly later for Mexican American (23 min), Non-Hispanic Asian (15 min), Non-Hispanic Black (46 min), and Other Hispanic (20 min) and Other Racial (14 min) adults (all p < 0.05). Mexican American and Non-Hispanic Asian adults had a significantly different last mealtime by 13 min earlier and 25 min later, respectively, compared to Non-Hispanic White adults. Compared to Non-Hispanic White adults, the mean eating duration was shorter for other Hispanic (20 min), Mexican American (36 min), and Non-Hispanic Black (49 min) adults. Conclusions: Meal timing and eating duration are additional dietary characteristics that vary significantly among racial and ethnic groups.