Scientific information

Magnesium

Magnesium is an essential mineral and a cofactor for over 325 enzymatic reactions involved in cellular energy production and storage, protein synthesis, DNA and RNA synthesis, cell growth and reproduction, adenylate cyclase synthesis, maintenance of cellular electrolyte composition, and stabilization of mitochondrial membranes. Magnesium plays a central role in the control of neuronal activity, cardiac excitability, neuromuscular transmission, muscular contraction, vasomotor tone, and blood pressure.

Magnesium (Mg2+) is a divalent metal ion. It is the fourth most abundant cation in the body after calcium (Ca2+), potassium (K+), and sodium (Na+) and is the second most abundant intracellular cation after potassium (K+).

Magnesium absorption

Magnesium absorption occurs throughout the entire intestinal tract, but the sites of maximal absorption are the distal jejunum and ileum. Two transport mechanisms are thought to be responsible for magnesium absorption in the intestinal tract, both a passive and an active transport system. The first is a saturable carrier-mediated mechanism that operates at low intake levels. The second mechanism is via simple diffusion across the intestinal mucosa when intakes of magnesium are high. The colon may also be involved in the absorption of magnesium, especially if disease has interfered with magnesium absorption or in cases of hypermagnesemia where solutions containing magnesium were administered by enema.

Organic forms of magnesium, such as citrate, are better absorbed, utilized, and assimilated than the inorganic forms such as magnesium oxide and hydroxide, which is why the latter two are often used as laxatives.

Walker et al. demonstrated that the organic forms of magnesium (citrate and amino-acid chelate) are more absorbable than magnesium oxide or placebo, as assessed by the 24-h urinary excretion after 60 days of daily supplementation. However, magnesium citrate was found to be the most bioavailable preparation compared with the other treatments studied, on account of it resulting in the greatest serum magnesium concentration following both acute and chronic daily supplementation compared with the other treatments studied or placebo. Further support for the conclusion that magnesium citrate had the best bioavailability of the Mg preparations studied came from the greater salivary magnesium concentration after 60 days of this treatment compared with all other treatments studied. Outcome data on magnesium oxide supplementation was no different from placebo – confirming its poor bioavailability.

Magnesium deficiency

Magnesium deficiency is usually associated with the presence of another illness or the use of a therapeutic agent. Magnesium may be lost via the gastrointestinal tract, either by excreted fluids or by impaired absorption of dietary and supplemental magnesium. Magnesium may also be lost due to vomiting, diarrhea, or fistula, and subsequently magnesium depletion is often seen in patients with chronic diarrhea, enteritis, ulcerative colitis, or an intestinal or biliary fistula.

Prolonged treatment with medications, including furesomide, aminoglycosides, amphotericin B, cisplatin, cyclosporine, and pentamidine, may also lead to magnesium depletion. In addition to medications, elevated blood alcohol level has been associated with hypermagnesuria.

Other cause of magnesium defgiciency include malabsorption syndromes such as celiac sprue, diabetes, hyperthyroidism, hyperparathyroidism, renal diseases, hypercalcemia. Increased magnesium excretion has beem observed also in athletes.

Magnesium and vitamin B6

Vitamin B6 (pyridoxine) plays a fundamental role in the active transport of minerals across cell membranes. Abraham et al. reported that following vitamin B6 administration, the mean plasma and red blood cell magnesium levels were significantly elevated, with a doubling of red blood cell levels after four weeks of therapy. Turnlund et al reported that in young women magnesium balance was negative during vitamin B6 depletion due to increased urinary magnesium excretion.

Magnesium and sports

Exercising accelerates metabolism and the requirement for magnesium may also increase. Athletes undergoing active anabolism and subjected to stress often have greater magnesium needs. Those athletes maintaining low body weights are at particular risk for magnesium deficiency.

Magnesium deficiency may result in athletes because intensive training increases both sweat loss and urinary excretion of the element. The losses of magnesium in sweat may be significant  when exercised in hot environment. Costill et al. reported that an intense training session in a hot environment may lead to a sweat loss of up to 2,8 l/h and may eliminate between 18 and 60 mg of magnesium per liter, representing 5 to 20 % of the recommended daily intake of magnesium.

Loss of intracellular magnesium may lead to muscle weakness, neuromuscular dysfunction, and cramping or spasms. Thus, the maintenance of intracellular magnesium is important for exercise performance.

The mechanism whereby high-intensity exercise may increase magnesium excretion are uncertain, but possible explanations have been proposed. One explanation is that exercise may be accompanied by transient impairment of the renal-concentrating mechanisms and thus local renal handling of magnesium may be disturbed. Furthermore, several hormones, such as aldosterone, antidiuretic hormone (ADH), and thyroid hormones, may cause hypermagnesuria by reducing tubular reabsorption of magnesium.

Exercise-induced rise in blood lactic acid may cause an elevation in plasma phosphorus and metabolic acidosis. Metabolic acidosis has also been shown to cause magnesuria by reducing renal tubular reabsorption of magnesium.

According to Seelig diets rich in magnesium and/or use of magnesium supplements is recommended to ensure magnesium intake of 6 to 10 mg/kg body weight per day.

References

Abraham GE, et al. Effect of vitamin B-6 on plasma and red blood cell magnesium levels in premenopausal women. Ann Clin Lab Sci 1981;11(4):333–336
:: Ann Clin Lab Sci, PubMed, Google Scholar

Bohl CH, Volpe SL. Magnesium and exercise. Critical Rev Food Sci Nutr 2002;42:533–563
:: DOI, PubMed, Google Scholar

Costill DL. Sweating: its composition and effect on body fluids. Ann N Y Acad Sci, 1977;301:160–170
:: DOI, PubMed, Google Scholar

Deuster PA, et al. Magnesium homeostasis during high-intensity anaerobic exercise in men. J Appl Physiol, 1987;62:545–550
:: J Appl Physiol, PubMed, Google Scholar

Fine KD, et al. Intestinal absorption of magnesium from food and supplements. J Clin Invest 1991;88:396–402
:: DOI, PubMed, Google Scholar

Kayne LH, Lee DB. Intestinal magnesium absorption. Miner Electrolyte Metab 1993;19:210–217
:: PubMed, Google Scholar

Lijnen P, et al. Erythrocyte, plasma and urinary magnesium in men before and after a marathon. Eur J Appl Physiol 1988;58:252–256
:: DOI, PubMed, Google Scholar

Newhouse IJ, Finstad EW. The effects of magnesium supplementation on exercise performance. Clin J Sport Med, 2000;10:195–200
:: Clin J Sport Med, PubMed, Google Scholar

Pokan R, et al. Oral magnesium therapy, exercise heart rate, exercise tolerance, and myocardial function in coronary artery disease patients. Br J Sports Med 2006;40:773–778
:: DOI, PubMed, Google Scholar

Rayssiguier Y, et al. New experimental and clinical data on the relationship between magnesium and sport. Magnes Res 1990;3:93–102
:: PubMed, Google Scholar

Rude RK. Magnesium. In: Biochemical and physiological aspects of human nutrition. Ed. Stipanuk MH. Saunders, Philadelphia, USA, 671–685, 2000
:: Elsevier, Google Scholar

Seelig MS. Consequences of magnesium deficiency on the enhancement of stress reactions; preventive and therapeutic implications (a review). J Am Coll Nutr 1994;13:429–446
:: J Am Coll Nutr, PubMed, Google Scholar

Shah GM, Kirschenbaum MA. Renal magnesium wasting associated with therapeutic agents. Miner Electrolyte Metab 1991;17:58–64
:: PubMed, Google Scholar

Turnlund JR, et al. Vitamin B-6 depletion followed by repletion with animal- or plant-source diets and calcium and magnesium metabolism in young women. Am J Clin Nutr 1992;56:905–910
:: Am J Clin Nutr, PubMed, Google Scholar

Walker AF, et al. Mg citrate found more bioavailable than other Mg preparations in a randomized, double-blind study. Magnes Res 2003;16:183–191
:: Magnes Res, PubMed, Google Scholar

Wester PO. Magnesium. Am J Clin Nutr 1987;45(suppl):1305–1312
:: Am J Clin Nutr, PubMed

Whang R, et al. Magnesium homeostasis and clinical disorders of magnesium deficiency. Ann Pharmacol 1994;28:220–226
:: Ann Pharmacol, PubMed, Google Scholar