Magnesium is one of the major mineral nutrients in the human body. Amounting to approximately 20–28 g of magnesium, 60% is found in the bones and teeth, with the remaining 40% located in muscle tissue.
Serum levels of magnesium range from 1.5–2.1mEq/L; it’s the second-most plentiful positively charged ion found within the cells of the body, signifying its importance in the multitudes of physiologic cellular functions. One of the most important metabolic process, the synthesis and consumption of ATP, is directly linked to magnesium. Magnesium-linked ATP processes activate approximately 300 different enzymes, which are involved in functions as diverse as DNA/RNA synthesis, glycolysis, intracellular mineral transport, nerve impulse generation, cell membrane electrical potential, muscle contraction, blood vessel tone and the regeneration of ATP.1
The adult Recommended Dietary Allowance (RDA) for magnesium is 350mg per day for men and 280mg for women. The typical American diet provides approximately 120mg per 1000 calories, meaning that a person that consumes fewer than 1500 calories is likely to be deficient in magnesium. The absorption rate of magnesium ranges from 24 to nearly 85%; magnesium derived from metallic sources is less absorbable, whereas that derived from plant sources is more easily absorbed.
Factors that increase the need for magnesium because of limited uptake or increased losses include excess phosphate consumption (soft drinks) and alcoholic beverages, high stress lifestyles, some diuretics, digitalis, strenuous exercise (high performance athletes lose a considerable amount of magnesium in sweat), pregnant and lactating women, individuals with diabetes, severe diarrhoea or kidney disease.
The early signs of magnesium deficiency include vague symptoms such as loss of appetite, stomachache and diarrhoea. Longer-term deficiency symptoms may manifest themselves as confusion, apathy, depression, irritability, arrhythmias, weakness, poor co-ordination, nausea, vomiting, electromyographic changes, muscle and nerve irritability, and tremors.2
Magnesium has many novel uses for common health conditions. As an antacid, magnesium salts react with gastric acid to form magnesium chloride, thereby neutralising hydrochloric acid. As a laxative, magnesium acts osmotically in the intestine and colon as well as triggering the release of gastrin and cholecystokinin, stimulating gastric motility. The inhibitory effect of magnesium on preterm labour contractions (tocolysis) is attributed to the antagonism of calcium-mediated uterine contractions, whereas the anticonvulsant actions of magnesium in eclampsia may result from the inhibition of neuromuscular transmission and a subsequent depressant effect on smooth muscle contraction.3
Magnesium and blood pressure
Magnesium has an important role in reducing blood pressure.4 Magnesium deficiency has been found to induce elevated intracellular concentrations of sodium and potassium, which results in increased peripheral resistance and vasospasm.5 Additionally, some research suggests that hypertensive patients with hypomagnesemia usually require more antihypertensive medications than hypertensive patients with normal magnesium levels.6
The early signs of magnesium deficiency include vague symptoms such as loss of appetite, stomachache and diarrhoea. Longer-term deficiency symptoms may manifest themselves as confusion, apathy, depression, irritability, arrhythmias, weakness, poor co-ordination, nausea, vomiting, electromyographic changes, muscle and nerve irritability, and tremors
Diets that contain plenty of fruits and vegetables, which are good sources of potassium and magnesium, are consistently associated with lower blood pressure.7 The effect of various nutritional factors on the incidence of high blood pressure was examined in more than 30,000 US male health professionals. After 4 years of follow up, it was found that a greater magnesium intake was significantly associated with a lower risk of hypertension.8 The Joint National Committee on Prevention, Detection, Evaluation and Treatment of High Blood Pressure recommends maintaining an adequate magnesium intake as a positive lifestyle modification to prevent and manage high blood pressure.9
Magnesium and heart disease
Magnesium may play a role in reducing coronary vascular resistance, increasing coronary artery blood flow parameters and preventing arrhythmias. Further, the inadequate intake and absorption of magnesium is associated with the development of disease processes such as hypertension, cardiomyopathy, atherosclerosis and stroke.10
Further evidence indicates that low body stores of magnesium actually increase the incidence of arrhythmias, which can increase the risk of cardiovascular complications.11 Surveys of the population in general have associated higher blood levels of magnesium with a lower risk of coronary heart disease.12 Additionally, dietary surveys have suggested that a higher magnesium intake is associated with a lower risk of stroke.13
Magnesium and osteoporosis
Magnesium deficiency may be a risk factor for post-menopausal osteoporosis. This may be related to the fact that magnesium deficiency negatively alters calcium metabolism and the hormone that regulates bone calcium stores.14 Several studies have suggested that magnesium supplementation may improve bone mineral density and that the low intake and impaired absorption of magnesium have also been associated with the development of osteoporosis.
Magnesium and diabetes
Magnesium plays an important role in carbohydrate metabolism, influencing the release and activity of insulin. Elevated blood glucose levels can increase the loss of magnesium in the urine, leading to increased magnesium loss from the body. Commonly, low magnesium serum levels are often seen in poorly controlled diabetics.
Magnesium and asthma
Magnesium plays a dynamic role in lung structure and function. It acts to block the function of calcium that, in the lungs, causes bronchial smooth-muscle contraction. The possibility exists that magnesium deficiency may contribute to lung complications. It is interesting to note that calcium consumption in the US has increased in the past few years; but, as there has been little change in magnesium intake, we’re witnessing an imbalance in the calcium:magnesium ratio.15
Further evidence indicates that low body stores of magnesium actually increase the incidence of arrhythmias, which can increase the risk of cardiovascular complications
This deficiency also has an effect on the activity of specific white blood cells (neutrophils) that, during an asthma attack, can worsen the condition. Researchers theorise that the low magnesium content of white blood cells has an important effect on the pathogenesis of asthma.16 It is additionally hypothesized that a high magnesium diet is directly related to healthy lung function and a reduced risk of airway hyper-reactivity and wheezing. Low magnesium intake may therefore be involved in the occurrence of asthma.17
The beneficial health effects of magnesium and its disease-prevention qualities emphasise the importance of this commonly overlooked mineral. As the fields of nutrition and medicine continue to reveal the benefits of magnesium, it becomes more and more apparent that supplementation with this mineral is vital to maintaining our health. Like all supplements, the proper supplementation of magnesium must be emphasised by seeking the advice of a qualified, nutritionally oriented physician.
References
1. M. Shils, A. Olson and M. Shike, Modern Nutrition in Health and Disease, Eighth Edition (Lea and Febiger, Philadelphia, Pennsylvania, USA, 1994).
2. E. Whitney, C.B. Cataldo and S.R. Rolfes (Eds), Understanding Normal and Clinical Nutrition (Wadsworth Publishing Co., Belmont, California, USA, 1998).
3. R. Swain and B. Kaplan-Machlis, 'Magnesium for the Next Millennium,' South Med. J. 92, 1040–1047 (1999).
4. Y. Yamori, et al., 'Nutritional Factors for Stroke and Major Cardiovascular Diseases: International Epidemiological Comparison of Dietary Prevention,' Health Rep. 6(1), 22–27 (1994).
5. S. Douban, et al., 'Significance of Magnesium in Congestive Heart Failure,' Am. Heart J. 132(3), 664–671 (1996).
6. B.T. Altura, et al., 'Low Levels of Serum Ionized Magnesium are Found in Patients Early After Stroke Which Result in Rapid Elevation in Cytosolic Free Calcium and Spasm in Cerebral Vascular Muscle Cells,' Neurosci. Lett. 230, 37–40 (1997).
7. A.P. Simopoulos, 'The Nutritional Aspects of Hypertension,' Compr. Ther. 25, 95–100 (1999).
8. A. Ascherio, et al., 'A Prospective Study of Nutritional Factors and Hypertension Among US Men,' Circulation 86, 1475–1484 (1992).
9. National Heart, Lung and Blood Institute, 'Joint National Committee on Prevention, Detection, Evaluation and Treatment of High Blood Pressure. The Sixth Report of the Joint National Committee on Prevention, Detection, Evaluation and Treatment of High Blood Pressure,' Arch. Intern. Med. 157, 2413–2446 (1997).
10. L.J. Appel, 'Nonpharmacologic Therapies That Reduce Blood Pressure: A Fresh Perspective,' Clin. Cardiol. 22, 1111–1115 (1999).
11. Institute of Medicine, Food and Nutrition Board, Dietary Reference Intakes: Calcium, Phosphorus, Magnesium, Vitamin D and Fluoride (National Academy Press, Washington, DC, USA, 1999).
12. E.S. Ford, 'Serum Magnesium and Ischaemic Heart Disease: Findings from a National Sample of US Adults,' Int. J. Epidem. 28, 645–651 (1999).
13. A. Ascherio, et al., 'Intake of Potassium, Magnesium, Calcium and Fiber and Risk of Stroke Among US Men,' Circulation 98, 1198–1204 (1998).
14. R.K. Rude and M. Olerich, 'Magnesium Deficiency: Possible Role in Osteoporosis Associated with Gluten-Sensitive Enteropathy,' Osteoporos. Int. 6, 453–461 (1996).
15. R.A. Landon and E.A. Young, 'Role of Magnesium in Regulation of Lung Function,' J. Am. Diet Assoc. 93(6), 674–677 (1993).
16. P. Fantidis, et al., 'Intracellular (Polymorphonuclear) Magnesium Content in Patients with Bronchial Asthma Between Attacks,' J. R. Soc. Med. 88(8), 441–445 (1995).
17. J. Britton, et al., 'Dietary Magnesium, Lung Function, Wheezing and Airway Hyperreactivity in a Random Adult Population Sample,' Lancet 344(8919), 357–362 (1994).
