Monday, 16 December 2013

Magnesium and Bone health

Magnesium is the eleventh most abundant element by mass in the human body. The adult body content is 25 g distributed in the skeleton and soft tissues. The chemical is essential in manipulating important biological polyphosphate such as ATP, DNA, and RNA and in functionming enzymes(a).
Magnesium and Bone health 
1. Nutrition and bone health. Magnesium and bone
Magnesium is related to a number of biological enzymatic reactions such as catalytic role for the reaction of kinases in ATP production. On the other hand, magnesium is one of the essential minerals for bone formation. According to the study by the National Institute of Health and Nutrition., in the magnesium-deficient rats, apparent bone loss caused by increase in bone resorption and decrease in bone formation was observed. Although, epidemiological studies suggest that magnesium deficiency is one of the risk factor for osteoporosis, a relationship between magnesium intake and bone mineral density is not clear. This may be due to the differences in the population, decrease in sex hormone secretion, and the possibility that magnesium-deficiency is also accompanied with another nutrient insufficiency, e.g., calcium(1).

2. Skeletal and hormonal effects of magnesium deficiency
Magnesium (Mg) is the second most abundant intracellular cation where it plays an important role in enzyme function and trans-membrane ion transport. Mg deficiency has been associated with a number of clinical disorders including osteoporosis. Osteoporosis is common problem accounting for 2 million fractures per year in the United States at a cost of over $17 billion dollars. The average dietary Mg intake in women is 68% of the RDA, indicating that a large proportion of our population has substantial dietary Mg deficits. In the study to review the evidence for Mg deficiency-induced osteoporosis and potential reasons why this occurs, including a cumulative review of work in our laboratories and well as a review of other published studies linking Mg deficiency to osteoporosis, showed that pidemiological studies have linked dietary Mg deficiency to osteoporosis. As diets deficient in Mg are also deficient in other nutrients that may affect bone, studies have been carried out with select dietary Mg depletion in animal models. Severe Mg deficiency in the rat (Mg at <0.0002% of total diet; normal = 0.05%) causes impaired bone growth, osteopenia and skeletal fragility. This degree of Mg deficiency probably does not commonly exist in the human population. We have therefore induced dietary Mg deprivation in the rat at 10%, 25% and 50% of recommended nutrient requirement. We observed bone loss, decrease in osteoblasts, and an increase in osteoclasts by histomorphometry. Such reduced Mg intake levels are present in our population(2).

3. Magnesium deficiency and osteoporosis: animal and human observations
Although osteoporosis is a major health concern for our growing population of the elderly, there continues to be a need for well-designed clinical and animal studies on the link between dietary magnesium (Mg) intake and osteoporosis. According to the study by the University of Southern California and The Orthopaedic Hospital, Los Angeles, relatively few animal studies have assessed the skeletal and hormonal impact of long-term low Mg intake; however, these studies have demonstrated that Mg deficiency results in bone loss. Potential mechanisms include a substance P-induced release of inflammatory cytokines as well as impaired production of parathyroid hormone and 1,25-dihydroxyvitamin D. Abnormal mineralization of bones may also contribute to skeletal fragility. Clinical studies have often varied greatly in study design, subject age, menopausal status and outcome variables that were assessed. Most studies focused on female subjects, thus pointing to the great need for studies on aging males. According to the U.S. Department of Agriculture, the mean Mg intake for males and females is 323 and 228 mg/day, respectively. These intake levels suggest that a substantial number of people may be at risk for Mg deficiency, especially if concomitant disorders and/or medications place the individual at further risk for Mg depletion(3).

4. Nutrition and bone health. Magnesium-rich foods and bone health
According to the study by the Kagawa Nutrition University, about 60% of magnesium in human body is present in the skeleton. Various foods are containing magnesium. The major sources are foods of plant origin like grain, vegetable and pulse. EAR (estimated average requirement) and RDA (recommended dietary allowance) are set for age 1 year or over in Japan. There may be a large number of people who have inadequate intake of magnesium judging by the results of the national nutrition survey. Adequate intakes of magnesium and also other nutrients related bone health are desired(4).

5. Magnesium and osteoporosis: current state of knowledge and future research directions
According to the study by the University of Milan,, a  tight control of magnesium homeostasis seems to be crucial for bone health. On the basis of experimental and epidemiological studies, both low and high magnesium have harmful effects on the bones. Magnesium deficiency contributes to osteoporosis directly by acting on crystal formation and on bone cells and indirectly by impacting on the secretion and the activity of parathyroid hormone and by promoting low grade inflammation. Less is known about the mechanisms responsible for the mineralization defects observed when magnesium is elevated. Overall, controlling and maintaining magnesium homeostasis represents a helpful intervention to maintain bone integrity(5).

6. Magnesium metabolism in 4 to 8 year old children
Magnesium (Mg) is a key factor in bone health, but few studies have evaluated Mg intake or absorption and their relationship with bone mineral content (BMC) or bone mineral density (BMD) in children. In the study to measure Mg intake, absorption, and urinary excretion in a group of children 4 to 8 yrs of age, found that a small, but significantly greater Mg absorption efficiency (percentage absorption) in males than females (67 ± 12% vs 60 ± 8%, p = 0.02) but no difference in estimated net Mg retention (average of 37 mg/day in both males and females). Relating dietary Mg intake to estimated Mg retention showed that an intake of 133 mg/day, slightly above the current Estimated Average Requirement (EAR) of 110 mg/day led to a net average retention of 10 mg/day, the likely minimum growth-related need for this age group. Covariate analysis showed that Mg intake and total Mg absorption, but not calcium intake or total absorption were significantly associated with both total body BMC and BMD. These results suggest that usual Mg intakes in small children in the United States meet dietary requirements in most but not all children. Within the usual range of children's diets in the United States, dietary Mg intake and absorption may be important, relatively unrecognized factors in bone health(6).

7. Maternal first-trimester diet and childhood bone mass
In the study to assess the association of maternal first-trimester dietary intake during pregnancy with childhood bone mass, showed that higher first-trimester maternal protein, calcium, and phosphorus intakes and vitamin B-12 concentrations were associated with higher childhood bone mass, whereas carbohydrate intake and homocysteine concentrations were associated with lower childhood bone mass (all P-trend < 0.01). Maternal fat, magnesium intake, and folate concentrations were not associated with childhood bone mass. In the fully adjusted regression model that included all dietary factors significantly associated with childhood bone mass, maternal phosphorus intake and homocysteine concentrations most-strongly predicted childhood bone mineral content (BMC) [β = 2.8 (95% CI: 1.1, 4.5) and β = -1.8 (95% CI: -3.6, 0.1) g per SD increase, respectively], whereas maternal protein intake and vitamin B-12 concentrations most strongly predicted BMC adjusted for bone area [β = 2.1 (95% CI: 0.7, 3.5) and β = 1.8 (95% CI: 0.4, 3.2) g per SD increase, respectively(7).

8. Magnesium intake mediates the association between bone mineral density and lean soft tissue in elite swimmers
In the study to o understand if Mg intake mediates the association between bone mineral density (BMD) and lean soft tissue (LST) in elite swimmers, showed that 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(8).

9. Bone and nutrition in elderly women: protein, energy, and calcium as main determinants of bone mineral density
In a cross-sectional study of 136 healthy Caucasian, postmenopausal women, free of medications known to affect bone, with bone mineral density (BMD) and body composition (lean and fat tissue) were measured by dual X-ray absorptiometry using specialized software for different skeletal sites, showed that independent influence of calcium, energy, and protein, examined separately and in multiple regression models on BMD of several skeletal sites. Magnesium, zinc and vitamin C were significantly related to BMD of several skeletal sites in multiple regression models (controlled for age, fat and lean tissue, physical activity and energy intake), each contributing more than 1% of variance. Serum PTH and 25(OH)D did not show significant association with bone mass(9).

10. Evaluation of magnesium intake and its relation with bone quality in healthy young Korean women
In a study to  evaluate Mg intake in healthy adults and its relation with bone quality of a total of 484 healthy young women in their early 20s, with anthropometric measurements, dietary intake survey using 3-day dietary records, and the bone quality of the calcaneus using quantitative ultrasounds were obtained and analyzed and average age, height, and weight of the subjects were respectively 20.20 years, 161.37 cm, and 54.09 kg, respectively, showed that the subject's average intake of energy was 1,543.19 kcal, and the average Mg intake was 185.87 mg/day. Mg intake per 1,000 kcal of consumed energy in our subjects was 119.85 mg. Subjects consumed 63.11% of the recommended intake for Mg. Food groups consumed with high Mg content in our subjects included cereals (38.62 mg), vegetables (36.97 mg), milk (16.82 mg), legumes (16.72 mg), and fish (16.50 mg). The level of Mg intake per 1,000 kcal showed significant correlation to the SOS in the calcaneus (r = 0.110, p < 0.05) after adjustment for age, BMI, and percent body fat. In addition, the intakes of Mg from potatoes (p < 0.001), legumes (p < 0.05), and fungi and mushrooms (p < 0.05) positively correlated with the SOS of the calcaneus. Tthe magnesium intake status of young Korean women aged 19-25 years is unsatisfactory. Improving dietary intake of Mg may positively impact bone quality in this population(10).

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