Magnesium retention from metabolic-balance studies in female adolescents: impact of race, dietary salt, and calcium

Casein phosphopeptide calcium chelation: preparation optimization, in vitro gastrointestinal simulated digestion, and peptide fragment exploration

BACKGROUND

Calcium is important in the formation of bones and teeth, cell metabolism, and other physiological activities. In this work, casein phosphopeptide-calcium chelate (CPP-Ca) was synthesized and the optimal process parameters for the chelation reaction were obtained. The bioavailability of calcium in CPP-Ca was investigated by in vitro gastrointestinal simulated digestion. The existence of phytic acid and oxalic acid in the digestion system was evaluated to clarify the calcium holding ability of casein phosphopeptide (CPP). Liquid chromatography-tandem mass spectrometry (LC-MS/MS) was used to identify oligopeptides from CPP-Ca.

RESULTS

The optimal process parameters for the chelation reaction were: peptide concentration 7.76 mgmL-1 , pH 8.54, and reaction temperature 43.3 °C. The digestion in vitro results indicated that the calcium release rate of CPP-Ca in the stomach for 2 h reached 85%, and about 50% of the ionized calcium was re-chelated with CPP in the intestine. Phytic acid and oxalic acid could lead to a sharp decrease in soluble calcium but around 50% of the calcium was still retained in the form of chelates in the presence of CPP. The LC-MS/MS identified 19 casein-derived oligopeptides after digestion, and calcium modifications were found on eight peptides derived from β-casein and αs2 -casein.

CONCLUSIONS

This study clarified the excellent calcium holding capacity of CPP in the presence of phytic acid and oxalic acid. Liquid chromatography-tandem mass spectrometry also revealed peptide changes, and identified peptides that chelate with calcium. These findings provided significant insights that could be relevant to the further utilization and product development of peptide-calcium chelate in the food industry. © 2023 Society of Chemical Industry.

Suggested Reference Ranges of Blood Mg and Ca Level in Childbearing Women of China: Analysis of China Adult Chronic Disease and Nutrition Surveillance (2015)

Background: Magnesium and calcium play a variety of biological roles in body functions. Reference values of these elements have not yet been systematically determined in China, especially in childbearing women. We proposed to establish the reference range of Mg, Ca, and Ca/Mg ratio in plasma and whole blood for 18–44 years healthy childbearing women in China. Method: A total of 1921 women of childbearing age (18–44 years) were randomly selected from the 2015 China National Nutrition and Health Survey by taking into account the regional types and monitoring points. Among them, 182 healthy women were screened out with a series strict inclusion criteria to study the reference ranges of elements. Fundamental indicators (weight, height, waist, blood pressure, total cholesterol, triglyceride, high-density lipoprotein cholesterol, low-density lipoprotein, fast glucose, HbA1c, blood pressure, uric acid) and elements concentrations in plasma and whole blood were collected. The 2.5th to 97.5th was used to represent the reference range of Mg, Ca, and Ca/Mg ratio. Results: The reference range of Mg, Ca, and Ca/Mg ratio in plasma were 0.75–1.13 mmol/L, 2.27–3.43 mmol/L, and 2.41–3.44, respectively. Additionally, the reference range of Mg, Ca, and Ca/Mg ratio in whole blood were 1.28–1.83 mmol/L, 1.39–2.26 mmol/L, and 0.90–1.66, respectively. According to the established reference range, the prevalence of magnesium deficiency was 4.79% in 1921 childbearing women, 21.05% in type 2 diabetes, and 5.63% in prediabetes. Conclusion: The reference values of Mg, Ca and Ca/Mg proportion in plasma and entire blood of healthy childbearing women can be utilized as a pointer to assess the status of component lack and over-burden. The lower limit of plasma Mg is in good agreement with the recommended criteria for the determination of hypomagnesemia.

Circulating Ionized Magnesium as a Measure of Supplement Bioavailability: Results from a Pilot Study for Randomized Clinical Trial

Oral supplementation may improve the dietary intake of magnesium, which has been identified as a shortfall nutrient. We conducted a pilot study to evaluate appropriate methods for assessing responses to the ingestion of oral magnesium supplements, including ionized magnesium in whole blood (iMg²⁺) concentration, serum total magnesium concentration, and total urinary magnesium content. In a single-blinded crossover study, 17 healthy adults were randomly assigned to consume 300 mg of magnesium from MgCl₂ (ReMag^®, a picosized magnesium formulation) or placebo, while having a low-magnesium breakfast. Blood and urine samples were obtained for the measurement of iMg²⁺, serum total magnesium, and total urine magnesium, during 24 h following the magnesium supplement or placebo dosing. Bioavailability was assessed using area-under-the-curve (AUC) as well as maximum (C_max) and time-to-maximum (T_max) concentration. Depending on normality, data were expressed as the mean ± standard deviation or median (range), and differences between responses to MgCl₂ or placebo were measured using the paired t-test or Wilcoxon signed-rank test. Following MgCl₂ administration versus placebo administration, we observed significantly greater increases in iMg²⁺ concentrations (AUC = 1.51 ± 0.96 vs. 0.84 ± 0.82 mg/dL•24h; C_max = 1.38 ± 0.13 vs. 1.32 ± 0.07 mg/dL, respectively; both p < 0.05) but not in serum total magnesium (AUC = 27.00 [0, 172.93] vs. 14.55 [0, 91.18] mg/dL•24h; C_max = 2.38 [1.97, 4.01] vs. 2.24 [1.98, 4.31] mg/dL) or in urinary magnesium (AUC = 201.74 ± 161.63 vs. 139.30 ± 92.84 mg•24h; C_max = 26.12 [12.91, 88.63] vs. 24.38 [13.51, 81.51] mg/dL; p > 0.05). Whole blood iMg²⁺ may be a more sensitive measure of acute oral intake of magnesium compared to serum and urinary magnesium and may be preferred for assessing supplement bioavailability.

The Problematic Use of Dietary Reference Intakes to Assess Magnesium Status and Clinical Importance

Determination of the public health concern about magnesium (Mg) in health and disease has been confounded by the lack of a practical measure of status. This has resulted in a lack of consistency in associating Mg deficiency with specific pathological conditions. Some attempts at associating Mg with a chronic disease have used the Dietary Reference Intakes (DRIs) as a status assessment measure. Use of current DRIs for Mg is problematic because recent evidence suggests that they should be updated and based on body weight. An evidence-based suggested Estimated Average Requirement (EAR) and Recommended Dietary Allowance (RDA) for a 70-kg individual is 175 and 250 mg/day, respectively. However, numerous dietary and physiological factors can affect the need for Mg and thus affect the use of the current or suggested new DRIs to assess Mg status. Calcium intakes above normal requirements can decrease Mg balance and exacerbate signs of Mg deficiency. Mg deficiency apparently occurs often in obesity because of increased need to counteract the inflammatory stress induced by adipose tissue dysfunction. Deficiency in anti-oxidant nutrients such as vitamin E and selenium can exacerbate a response to low dietary Mg indicated by increased oxidative stress which can lead to chronic disease. Dietary modifiers of Mg absorption and excretion affect balance and thus the need for Mg. Factors decreasing Mg balance include low dietary protein and non-fermentable fiber, while factors that can increase balance include fructose and fermentable fiber and fructose-containing oligosaccharides. Use of the DRIs to assess the Mg status of a population or group needs to consider their physiological characteristics and dietary habits and be aware that the DRIs may need updating. The DRIs only can be considered a component of a toolbox that presently includes serum Mg concentration and the daily urinary Mg excretion to assess the Mg status of an individual.

Compact DD generator-based in vivo neutron activation analysis (IVNAA) system to determine sodium concentrations in human bone

OBJECTIVE

This study presents the development of a noninvasive method for monitoring Na in human bone. Many diseases, such as hypertension and osteoporosis, are closely associated with sodium (Na) retention in the human body. Na retention is generally evaluated by calculating the difference between dietary intake and excretion. There is currently no method to directly quantify Na retained in the body. Bone is a storage for many elements, including Na, which renders bone Na an ideal biomarker to study Na metabolism and retention.

APPROACH

A customized compact deuterium-deuterium (DD) neutron generator was used to produce neutrons for in vivo neutron activation analysis (IVNAA), with a moderator/reflector/shielding assembly optimized for human hand irradiation in order to maximize the thermal neutron flux inside the irradiation cave and to limit radiation exposure to the hand and the whole body.

MAIN RESULTS

The experimental results show that the system is able to detect sodium levels in the bone as low as 16 µg Na g^-1 dry bone with an effective dose to the body of about 27 µSv. The simulation results agree with the numbers estimated from the experiment.

SIGNIFICANCE

This is expected to be a feasible method for measuring the change of Na in bone. The low detection limit indicates this will be a useful system to study the association between Na retention and related diseases.

The effect of dietary magnesium and caseinphosphopeptides on bone metabolism in rats

The effect of dietary magnesium (Mg) or caseinphosphopeptides (CPPs) on bone metabolism has been reported. However, few studies have investigated the effects of simultaneous supplementation of Mg and CPPs. Sixty-three 3-week-old Sprague-Dawley male rats were divided into seven groups and fed a specified diet for 45 days. Body characteristics, bone physicochemical indicators, and bone metabolism indicators relative to bone metabolism were analyzed. We found that, first, a dietary Mg deficiency resulted in increased bone formation and decreased bone resorption. Second, dietary Mg or CPP supplementation promoted bone formation and prevented bone resorption. Third, dietary Mg supplementation with CPPs also functioned to enhance bone formation and prevent bone resorption. There were synergistic effects on femur length, serum parathyroid hormone level and urinary deoxypyridinoline of the HS-Mg-CPP group (0.2% Mg, 0.1% CPPs). The increase in the femur length of the HS-Mg-CPP group compared with the control group was 6% which was much higher than that of HS-Mg (1%) or CPPs (5%). The induction in serum parathyroid hormone content in the HS-Mg-CPP group was 33% compared with the control group which was higher than that of the induction of the HS-Mg (19%) or CPP (23%) group. The induction in the deoxypyridinoline content of the HS-Mg-CPP (43%) group compared with the control group was remarkably higher than that of HS-Mg (8%) or CPPs (16%). Overall our results demonstrated that high doses of Mg (0.2%) and CPPs (0.1%) in combination produced synergistic effects on femur length, serum parathyroid hormone level and urinary deoxypyridinoline in rats, which is important for a better understanding of the effect of Mg and CPPs on bone metabolism.

Individual variation in urinary sodium excretion among adolescent girls on a fixed intake

BACKGROUND

According to traditional understanding of sodium homeostasis, nearly all of daily sodium intake is excreted in urine, with intraindividual variability attributed to variability in dietary sodium intake and urine collection errors.

OBJECTIVE

To analyze the variability of urinary sodium in excretion from a balance study with fixed sodium intakes.

METHODS

Daily 24-h urine collections were assessed for sodium, potassium, and creatinine in 22 black and 13 white adolescent girls (11-15 year, BMI 15-29 kg/m) in a randomized, crossover design with controlled diets containing either low (57 mmol/day) or high (167 mmol/day) sodium, each fed for 3 weeks.

RESULTS

Coefficient of variation analysis indicated higher variation in urinary sodium excretion about the mean on low (vs high) sodium (40 vs 32%, P = 0.02) and in black (vs white) girls (42 vs 30%, P < 0.001). A mixed model showed no sodium intake × race interaction. Urinary sodium excretion was not correlated with urinary potassium or creatinine excretion. Excretion of 65 mmol/day (adequate intake) or less was documented on 16% on the days during the high-sodium diet. Reliability of the mean of several urine sodium samples varied from 23% for one sample to 75% for 10 samples for the high-sodium diet.

CONCLUSION

The high intraindividual variability in urinary sodium excretion on a fixed diet highlights the potential for substantial error in (a) using a single 24-h urine collection to estimate an individual's usual sodium intake and (b) relating sodium excretion from a single 24-h collection with outcomes. Further research is warranted to understand the causes of such variation.

Data from Controlled Metabolic Ward Studies Provide Guidance for the Determination of Status Indicators and Dietary Requirements for Magnesium

Determination of whether magnesium (Mg) is a nutrient of public health concern has been hindered by questionable Dietary Recommended Intakes (DRIs) and problematic status indicators that make Mg deficiency assessment formidable. Balance data obtained since 1997 indicate that the EAR and RDA for 70-kg healthy individuals are about 175 and 250 mg/day, respectively, and these DRIs decrease or increase based on body weight. These DRIs are less than those established for the USA and Canada. Urinary excretion data from tightly controlled metabolic unit balance studies indicate that urinary Mg excretion is 40 to 80 mg (1.65 to 3.29 mmol)/day when Mg intakes are <250 mg (10.28 mmol)/day, and 80 to 160 mg (3.29 to 6.58 mmol)/day when intakes are >250 mg (10.28 mmol)/day. However, changing from low to high urinary excretion with an increase in dietary intake occurs within a few days and vice versa. Thus, urinary Mg as a stand-alone status indicator would be most useful for population studies and not useful for individual status assessment. Tightly controlled metabolic unit depletion/repletion experiments indicate that serum Mg concentrations decrease only after a prolonged depletion if an individual has good Mg reserves. These experiments also found that, although individuals had serum Mg concentrations approaching 0.85 mmol/L (2.06 mg/dL), they had physiological changes that respond to Mg supplementation. Thus, metabolic unit findings suggest that individuals with serum Mg concentrations >0.75 mmol/L (1.82 mg/L), or as high as 0.85 mmol/L (2.06 mg/dL), could have a deficit in Mg such that they respond to Mg supplementation, especially if they have a dietary intake history showing <250 mg (10.28 mmol)/day and a urinary excretion of <80 mg (3.29 mmol)/day.

Perspective: The Case for an Evidence-Based Reference Interval for Serum Magnesium: The Time Has Come

The 2015 Dietary Guidelines Advisory Committee indicated that magnesium was a shortfall nutrient that was underconsumed relative to the Estimated Average Requirement (EAR) for many Americans. Approximately 50% of Americans consume less than the EAR for magnesium, and some age groups consume substantially less. A growing body of literature from animal, epidemiologic, and clinical studies has demonstrated a varied pathologic role for magnesium deficiency that includes electrolyte, neurologic, musculoskeletal, and inflammatory disorders; osteoporosis; hypertension; cardiovascular diseases; metabolic syndrome; and diabetes. Studies have also demonstrated that magnesium deficiency is associated with several chronic diseases and that a reduced risk of these diseases is observed with higher magnesium intake or supplementation. Subclinical magnesium deficiency can exist despite the presentation of a normal status as defined within the current serum magnesium reference interval of 0.75-0.95 mmol/L. This reference interval was derived from data from NHANES I (1974), which was based on the distribution of serum magnesium in a normal population rather than clinical outcomes. What is needed is an evidenced-based serum magnesium reference interval that reflects optimal health and the current food environment and population. We present herein data from an array of scientific studies to support the perspective that subclinical deficiencies in magnesium exist, that they contribute to several chronic diseases, and that adopting a revised serum magnesium reference interval would improve clinical care and public health.

Urinary Mineral Concentrations in European Pre-Adolescent Children and Their Association with Calcaneal Bone Quantitative Ultrasound Measurements

This study investigates differences and associations between urinary mineral concentrations and calcaneal bone measures assessed by quantitative ultrasonography (QUS) in 4322 children (3.1–11.9 years, 50.6% boys) from seven European countries. Urinary mineral concentrations and calcaneal QUS parameters differed significantly across countries. Clustering revealed a lower stiffness index (SI) in children with low and medium urinary mineral concentrations, and a higher SI in children with high urinary mineral concentrations. Urinary sodium (uNa) was positively correlated with urinary calcium (uCa), and was positively associated with broadband ultrasound attenuation and SI after adjustment for age, sex and fat-free mass. Urinary potassium (uK) was negatively correlated with uCa but positively associated with speed of sound after adjustment. No association was found between uCa and QUS parameters after adjustment, but when additionally adjusting for uNa, uCa was negatively associated with SI. Our findings suggest that urinary mineral concentrations are associated with calcaneal QUS parameters and may therefore implicate bone properties. These findings should be confirmed in longitudinal studies that include the food intake and repeated measurement of urinary mineral concentrations to better estimate usual intake and minimize bias.

Biomarkers for nutrient intake with focus on alternative sampling techniques

Biomarkers of nutrient intake or nutrient status are important objective measures of foods/nutrients as one of the most important environmental factors people are exposed to. It is very difficult to obtain accurate data on individual food intake, and there is a large variation of nutrient composition of foods consumed in a population. Thus, it is difficult to obtain precise measures of exposure to different nutrients and thereby be able to understand the relationship between diet, health, and disease. This is the background for investing considerable resources in studying biomarkers of nutrients believed to be important in our foods. Modern technology with high sensitivity and specificity concerning many nutrient biomarkers has allowed an interesting development with analyses of very small amounts of blood or tissue material. In combination with non-professional collection of blood by finger-pricking and collection on filters or sticks, this may make collection of samples and analyses of biomarkers much more available for scientists as well as health professionals and even lay people in particular in relation to the marked trend of self-monitoring of body functions linked to mobile phone technology. Assuming standard operating procedures are used for collection, drying, transport, extraction, and analysis of samples, it turns out that many analytes of nutritional interest can be measured like metabolites, drugs, lipids, vitamins, minerals, and many types of peptides and proteins. The advantage of this alternative sampling technology is that non-professionals can collect, dry, and mail the samples; the samples can often be stored under room temperature in a dry atmosphere, requiring small amounts of blood. Another promising area is the potential relation between the microbiome and biomarkers that may be measured in feces as well as in blood.

The National Osteoporosis Foundation's position statement on peak bone mass development and lifestyle factors: a systematic review and implementation recommendations

Lifestyle choices influence 20-40 % of adult peak bone mass. Therefore, optimization of lifestyle factors known to influence peak bone mass and strength is an important strategy aimed at reducing risk of osteoporosis or low bone mass later in life. The National Osteoporosis Foundation has issued this scientific statement to provide evidence-based guidance and a national implementation strategy for the purpose of helping individuals achieve maximal peak bone mass early in life. In this scientific statement, we (1) report the results of an evidence-based review of the literature since 2000 on factors that influence achieving the full genetic potential for skeletal mass; (2) recommend lifestyle choices that promote maximal bone health throughout the lifespan; (3) outline a research agenda to address current gaps; and (4) identify implementation strategies. We conducted a systematic review of the role of individual nutrients, food patterns, special issues, contraceptives, and physical activity on bone mass and strength development in youth. An evidence grading system was applied to describe the strength of available evidence on these individual modifiable lifestyle factors that may (or may not) influence the development of peak bone mass (Table 1). A summary of the grades for each of these factors is given below. We describe the underpinning biology of these relationships as well as other factors for which a systematic review approach was not possible. Articles published since 2000, all of which followed the report by Heaney et al. [1] published in that year, were considered for this scientific statement. This current review is a systematic update of the previous review conducted by the National Osteoporosis Foundation [1]. [Table: see text] Considering the evidence-based literature review, we recommend lifestyle choices that promote maximal bone health from childhood through young to late adolescence and outline a research agenda to address current gaps in knowledge. The best evidence (grade A) is available for positive effects of calcium intake and physical activity, especially during the late childhood and peripubertal years-a critical period for bone accretion. Good evidence is also available for a role of vitamin D and dairy consumption and a detriment of DMPA injections. However, more rigorous trial data on many other lifestyle choices are needed and this need is outlined in our research agenda. Implementation strategies for lifestyle modifications to promote development of peak bone mass and strength within one's genetic potential require a multisectored (i.e., family, schools, healthcare systems) approach.

Parallels between nutrition and physical activity: research questions in development of peak bone mass

Lifestyle choices are attributed to 40% to 60% of adult peak bone mass. The National Osteoporosis Foundation (NOF) sought to update its 2000 consensus statement on peak bone mass and partnered with the American Society for Nutrition, which, in turn, charged a 9-member writing committee with using a systematic review approach to update the previous NOF guidelines. PubMed searches of the scientific literature from January 2000 through December 2014 were conducted on all relevant lifestyle choice factors and their relation to increasing bone mass during childhood and adolescence. The writing group concluded that there is strong evidence for the benefits of physical activity and calcium intake on bone mass accretion, moderately strong evidence for the benefits of vitamin D and dairy intake on bone mass and for physical activity on bone structure, and weaker evidence for other lifestyle choices. There were parallels and synergies between the benefits of diet and exercise on development of peak bone mass, but the type of evidence and public policy recommendations in the two disciplines differ in several important ways. Nutrition uses a more reductionist approach in contrast to physical activity, which uses a more global approach. This leads to differences in research priorities in the 2 disciplines. The disciplines can advance more quickly through collaboration and adoption of the best approaches from each other.

Silicon balance in human volunteers; a pilot study to establish the variance in silicon excretion versus intake

Background

Accumulating evidence suggests a role for silicon in optimal connective tissue health. Further proof of its importance/essentiality may be provided by studies involving imposed depletion followed by ²⁹Si challenge to estimate metabolic balance. Prior to conducting these expensive studies, we first established the variance of estimating normal Si excretion versus intake using a single oral dose of typical dietary Si, orthosilicic acid.

Methods

Healthy volunteers were recruited from Loei Rajabhat University, separated into two matched groups (three males and three females/group) and maintained on a standardized diet for the three study days. One group ingested 500 ml water containing orthosilicic acid (28.9 mg Si) and the other group received 500 ml water alone, all on a fasted stomach. Blood samples and total urine and faeces were collected over the 48 h post-dose period and 24 h before-hand (baseline) and analysed for silicon by inductively coupled plasma optical emission spectrometry.

Results

Serum Si analysis confirmed the ready absorption of silicon from the orthosilicic acid solution. Mean total urinary and faecal Si excretions over the 24 h post-dose period accounted for 57 ± 9.5% and 39 ± 9.4% of the ingested dose, respectively. Thus in total 96.3 ± 5.8% of the ingested dose was recovered in faecal plus urinary excretions over the 24 h post-dose period.

Conclusions

We report that in healthy subjects (presumably in Si balance), the ingestion of a soluble dose of dietary Si results in the same quantity (within analytical error) being excreted within 24 h. It is currently not known if this all originated from the dose solution or if there was some exchange with the body Si pool but, given the low variance in these silicon balance data, isotopic studies are now merited.