Cristina P. Monteiro

Role of cellular magnesium in health and human disease.

The aim of this paper is to discuss, on the basis of an extensive literature review, the role of magnesium in health and disease. Magnesium is an essential cation playing a crucial role in many physiological functions. It is critical in energy-requiring metabolic processes, in protein synthesis, membrane integrity, nervous tissue conduction, neuromuscular excitability, muscle contraction, hormone secretion, and in intermediary metabolism. Serum magnesium concentration is maintained within a narrow range by the small intestine and kidney which both increase their fractional magnesium absorption under conditions of magnesium deprivation. If magnesium depletion continues, the bone store helps to maintain serum magnesium concentration by exchanging part of its content with extracellular fluid. The abundance of magnesium within cells is consistent with its relevant role in regulating tissue and cell functions. Recent data suggest that large fluxes of magnesium can cross the cell plasma membrane in either direction following a variety of hormonal and non-hormonal stimuli, resulting in major changes in total and, to a lesser extent, in free magnesium content within tissues. Imbalances of magnesium are common and are associated with a great number of pathological situations responsible for human morbidity and mortality. A large part of the population may have an inadequate magnesium intake, and in particular elderly subjects and athletes may be prone to chronic latent magnesium deficiency. Magnesium deficit is frequently observed in alcoholics and diabetic patients, in whom a combination of factors contributes to its pathogenesis. We will discuss some of the aspects of the involvement of magnesium in the etiology of some pathological situations, such as cardiovascular diseases, diabetes, pre-eclampsia, eclampsia, sickle cell disease and chronic alcoholism.

Magnesium, Insulin Resistance and Body Composition in Healthy Postmenopausal Women

Objective: This study was conducted to determine the association between magnesium (Mg), body composition and insulin resistance in 136 sedentary postmenopausal women, 50 to 77 years of age. Methods: Diabetics, hypertensives and women on hormonal replacement therapy were excluded and the remaining 74 were divided according to BMI≥25 (obese: OG) and BMI<25 kg/m2 (non-obese: NOG). Nutritional data disclosed that intakes were high for protein and saturated fat, low for carbohydrates, polyunsaturated fat and Mg and normal for the other nutrients, according to recommended dietary allowances (RDA). Mg values in red blood cells (RBC-Mg) and plasma (P-Mg), were determined, as were fasting glucose, and insulin levels, Homeostasis Model Assessment (HOMA), body mass index (BMI), body fat percent (BF %), abdominal fat (AF) and free fat mass (FFM). Results: RBC-Mg values were low in both groups when compared with normal values. There were significant differences in body composition parameters, HOMA and insulin levels, with higher basal insulin levels in OG. RBC-Mg was directly correlated with insulin, HOMA and FFM in both groups, according to Pearson correlations. HOMA in OG was also directly correlated with BMI, FFM and AF. In NOG, HOMA was only correlated with FFM. The low RBC-Mg levels observed were probably due to low Mg intake and to deregulation of factors that control Mg homeostasis during menopause. Conclusions: Both Mg deficit and obesity may independently lead to a higher risk for insulin resistance and cardiovascular disease.

Magnesium intake is associated with strength performance in elite basketball, handball and volleyball players

Magnesium plays significant roles in promoting strength. Surveys of athletes reveal that intake of magnesium is often below recommended levels. We aimed to understand the impact of magnesium intake on strength in elite male basketball, handball, and volleyball players. Energy and nutrient intake were assessed from seven-day diet record. Strength tests included maximal isometric trunk flexion, extension, and rotation, handgrip, squat and countermovement Abalakov jump, and maximal isokinetic knee extension and flexion peak torques. Linear regression models were performed with significance at p<0.1. Mean magnesium intake was significantly lower than the recommended daily allowance. Regression analysis indicated that magnesium was directly associated with maximal isometric trunk flexion, rotation, and handgrip, with jumping performance tests, and with all isokinetic strength variables, independent of total energy intake. The observed associations between magnesium intake and muscle strength performance may result from the important role of magnesium in energetic metabolism, transmembrane transport and muscle contraction and relaxation.

Magnesium and strength in elite judo athletes according to intracellular water changes

Magnesium (Mg) deficiency strongly affects muscle performance. In judo, many athletes often undergo impressive weight changes associated with severe dehydration. Common practices used by athletes to achieve a target weight can lead to Mg deficit. This study aimed to understand the impact of Mg changes on strength from periods of weight stability to prior to competition in a sample of elite judo athletes who differentially changed their intracellular water (ICW). The sample consisted of 20 elite male judo athletes. Subjects were divided according to ICW changes: losses below 2% and losses equal to or above 2%. Mg was measured in serum, red blood cells and urine by atomic absorption spectrophotometry. ICW was calculated as the difference between total-body water and extracellular water using dilution techniques. Maximal handgrip strength was evaluated using Jamar Hydraulic Hand Dynamometer. Upper-body power was determined in a bench press. Higher ICW decreases were associated with higher strength reductions, though our results suggest that an increase in red blood cell Mg might attenuate those strength reductions in athletes who decrease the ICW compartment. As Mg losses can be considerable and intake is frequently insufficient, athletes should consider supplementation, especially during periods of weight reduction.

Magnesium intake mediates the association between bone mineral density and lean soft tissue in elite swimmers

Magnesium (Mg) deficiency has been associated with bone disorders. Physical activity is also crucial for bone mineralization. Bone mass loss has been observed to be accelerated in subjects with low Mg intake. We aim to understand if Mg intake mediates the association between bone mineral density (BMD) and lean soft tissue (LST) in elite swimmers. Seventeen elite swimmers (eight males; nine females) were evaluated. Bone mineral content, BMD, LST, and fat mass were assessed using dual energy X-ray absorptiometry. Energy and nutrient intake were assessed during a seven-day period and analyzed with Food Processor SQL. Males presented lower values than the normative data for BMD. Mg, phosphorus (P) and vitamin D intake were significantly lower than the recommended daily allowance. A linear regression model demonstrated a significant association between LST and BMD. When Mg intake was included, we observed that this was a significant, independent predictor of BMD, with a significant increase of 24% in the R(2) of the initial predictive model. When adjusted for energy, vitamin D, calcium, and P intake, Mg remained a significant predictor of BMD. In conclusion, young athletes engaged in low impact sports, should pay special attention to Mg intake, given its potential role in bone mineral mass acquisition during growth.

Magnesium and phase angle: a prognostic tool for monitoring cellular integrity in judo athletes.

Adequate magnesium (Mg) levels play a vital role in membrane excitability, cell contractility and metabolism, being a key nutrient for sustaining appropriate muscular contraction and performance levels in athletes. Phase angle (PhA), assessed by bioimpedance analysis (BIA), has been reported to be positively associated with most nutritional markers and is an indicator of membrane integrity and water distribution between intra- and extracellular spaces. The aim of the present study was to verify the association between Mg status and PhA as a predictor of cellular health, in a sample of judo athletes from a period of weight stability to prior to competition. Judo athletes (n = 20) from the national team were evaluated on two occasions: during a period when body weight was stable (M1), and prior to competition (M2). Changes between these occasions were calculated as M2-M1. PhA was obtained by bioelectrical impedance spectroscopy at a frequency of 50 KHz. Mg was measured in serum and red blood cells (RBC) by atomic absorption spectrophotometry, and Mg in the diet was assessed from a 24-h diet record over a seven-day period, after an assessment of body composition. Mean PhA did not differ from M1 to M2. However, individual changes in PhA were positively associated with individual changes in serum (r = 0.62, p = 0.004) and RBC Mg (r = 0.45, p = 0.048). This association was independent of weight changes between assessments, but when adjusted for Mg intake changes, only the association between PhA and serum Mg remained significant. These results highlight that in elite athletes PhA may be an indirect indicator of muscular function.

Immune cell changes in response to a swimming training session during a 24-h recovery period

Understanding the impact of training sessions on the immune response is crucial for the adequate periodization of training, to prevent both a negative influence on health and a performance impairment of the athlete. This study evaluated acute systemic immune cell changes in response to an actual swimming session, during a 24-h recovery period, controlling for sex, menstrual cycle phases, maturity, and age group. Competitive swimmers (30 females, 15 ± 1.3 years old; and 35 males, 16.5 ± 2.1 years old) performed a high-intensity training session. Blood samples were collected before, immediately after, 2 h after, and 24 h after exercise. Standard procedures for the assessment of leukogram by automated counting (Coulter LH 750, Beckman) and lymphocytes subsets by flow cytometry (FACS Calibur BD, Biosciences) were used. Subjects were grouped according to competitive age groups and pubertal Tanner stages. Menstrual cycle phase was monitored. The training session induced neutrophilia, lymphopenia, and a low eosinophil count, lasting for at least 2 h, independent of sex and maturity. At 24 h postexercise, the acquired immunity of juniors (15-17 years old), expressed by total lymphocytes and total T lymphocytes (CD3(+)), was not fully recovered. This should be accounted for when planning a weekly training program. The observed lymphopenia suggests a lower immune surveillance at the end of the session that may depress the immunity of athletes, highlighting the need for extra care when athletes are exposed to aggressive environmental agents such as swimming pools.

Coordination between antioxidant defences might be partially modulated by magnesium status

The aim of this study was to compare the redox balance in competitive adult swimmers against recreational practitioners, controlling for Mg intake. Fifteen, competitive swimmers and 16 recreational practitioners, all male and aged 18-25years, were recruited into the study. Oxidative and muscle damage markers, and antioxidant enzymes and non-enzymatic antioxidants were evaluated by photometry (except for thiobarbituric reactive substances (TBARS), which was assessed by fluorimetry). Controlling for the level of exercise, inverse correlations were observed for uric acid and glutathione reductase (GR) or susceptibility of red blood cells to peroxidation (RBCPx); plasma adrenaline oxidase activity (AdOx) and carotenoids; TBARS and GR or Vit E; and direct correlations were observed between AdOx and creatine kinase (CK) or TBARS; CK and superoxide dismutase activity; GR and RBCPx. Controlling for Mg intake in addition to exercise level revealed new inverse correlations: between carotenoids and TBARS or lactate, and new direct correlations between lactate and AdOx or TBARS; cortisol and AdOx, CK, lactate dehydrogenase, or methemoglobin reductase. The associations between uric acid and RBCPx; AdOx and CK or TBARS; and GR and RBCPx lost their significance. All others remained significant. These outcomes suggest that the coordination between antioxidant defences may be partially modulated by Mg, which may be the result of its ability to stabilize cell membranes and oxidation targets, such as adrenaline.

The Association Between Whey Protein, Regional Fat Mass and Strength in Resistance-Trained Men: A Cross-Sectional Study

The purpose of this study was to evaluate the association between whey protein supplementation, body composition, and muscle strength in resistance-trained individuals. Forty-nine healthy males, aged 18 to 35 years and were engaged in resistance training for at least 1 year, were assigned into 2 groups according to whey protein intake (whey - n = 26, age: 30.7 ± 7.4 years, body mass: 75.8 ± 9.0 kg; without whey: n = 23, age: 31.0 ± 7.4 years, body mass: 77.9 ± 9.3 kg). Using a cross-sectional design, a morning assessment of body fat mass (FM) (by dual-energy X-ray absorptiometry) and strength (using 1-repetition maximum for bench press and back squat) was performed. Nutritional assessment was performed by 3-day food records. Regarding nutritional habits, differences between total energy intake (kcal) and estimated energy requirements (kcal) were observed. Results, from raw data or controlling for energy intake, estimated energy requirements, or achieved percentage of energy requirements, showed that whey protein supplementation was inversely correlated with whole-body FM (R = -0.367 (p = 0.010); R = -0.317 (p = 0.049); R = -0.380 (p = 0.011); R = -0.321 (p = 0.047), respectively), trunk FM (R = -0.396 (p = 0.005), R = -0.367 (p = 0.022), R = -0.423 (p = 0.004), R = -0.369 (p = 0.021), respectively) and android FM (R = -0.381 (p = 0.007), R = -0.332 (p = 0.039), R = -0.383 (p = 0.010), R = -0.336 (p = 0.036), respectively). No correlations were found between muscle strength outcomes and whey protein supplementation. The present data suggest that whey protein ingestion has a positive association with whole-body and regional (trunk and android) FM.