Magnesium: A Best-Kept Secret

By Emmett Hughes, DC, MS

Magnesium is the second most abundant intracellular positive ion, with potassium the most abundant. Sixty percent of the body’s magnesium is found in bone, 25 percent in muscle and the remainder in soft tissue and fluids, especially gastric juice. The majority of magnesium in muscle is found in the mitochondria, where it is thought to play a role in permeability of the outer membrane.1

Dietary intake of magnesium has gone down dramatically over the past 100 years. It is estimated that 68 to 80 percent of Americans are magnesium deficient.2-4 In places where water is harder, levels of magnesium are higher, and the incidence of coronary artery disease is lower. It appears, however, that 8 million deaths from sudden cardiac failure occurred in the United States between 1940 and 1994 because of magnesium deficiency.5-8

Testing and Absorption
Serum levels are a poor indicator of magnesium status. Heart muscle levels are almost 20 times higher than serum levels, so measuring white blood cell levels is a more sensitive test. The best test is ionic magnesium measurement or elemental X-ray analysis using a buccal smear. However, none of these methods are definitive.9,10

The rate of magnesium absorption is highly variable, estimated to be from as low as 24 percent to as high as 85 percent. It is mainly absorbed in the jejunum via facilitated diffusion and simple diffusion, with smaller amounts absorbed in the ileum and colon. Many factors regulate magnesium absorption, including vitamin D levels.11 As calcium levels go down, magnesium absorption increases. High intakes of calcium, protein, vitamin D and alcohol all increase magnesium requirements.

Health Functions
Magnesium performs many vital functions. It regulates the absorption of calcium and is involved in the structural integrity of bone. Without adequate magnesium, bones will be dense, but trabecular bone will have poor integrity. Northern European countries, where the calcium to magnesium ratio is 4:1, have the highest rates of osteoporosis, as well.12 

Magnesium has an effect of relaxing smooth muscle and is therefore useful in conditions such as hypertension, dysmenorrhea, constipation, asthma, angina, stroke and myocardial infarct. It decreases coagulation and acts as a calcium channel blocker, helping the heart to pump more effectively and regulating blood pressure.13-15 It is involved in the function of more than 300 enzymes, as well as in regulating muscle contractility and nerve impulses. Virtually all body systems also rely on magnesium for at least some of their metabolic functions.16-19

Dietary Requirements and Sources
Requirements of magnesium vary with age and certain conditions. The RDA for males is 350 mg/day; for females 280 mg/day, with pregnancy and lactation requiring 350 mg/day. Optimal intake is estimated to be between 600 and 800 mg/day. The best dietary sources of magnesium are whole grains, nuts and fruits. These include soy flour, buckwheat flour, tofu, figs, cashews, avocado, millet and brewer’s yeast.20

Magnesium Deficiency
Symptoms of magnesium deficiency can mimic many other disorders. These include fatigue, irritability, weakness, dysmenorrhea, muscle spasms or tightness, cardiomyopathy, anorexia, sugar cravings, hypertension, anxiety and poor nail growth.21-25 Deficiency can result from kidney disease and intake of diuretics and can cause depletion of potassium intracellularly and affect muscles and bones. Besides low intake, magnesium deficiency can be caused by malabsorption syndromes, hyperthyroidism, kwashiorkor, diabetes mellitus, alcoholism, pancreatitis, parathyroid disorders, high dietary phytic acid and diarrhea.26-28

The clinical use of magnesium can be applied to a variety of conditions. These include constipation, muscle cramping, torticollis, acute angina following a myocardial infarct or stroke, asthma, kidney stone prevention (especially when given with vitamin B6) and dysmenorrhea. Other candidates for magnesium supplementation are GI spasms or cramping, eclampsia, heart disease29,30 (especially cardiomyopathy), diabetes mellitus, nocturnal muscle cramps, mitral valve prolapse, toxemia of pregnancy, fibromyalgia, migraine headaches, lead toxicity, general fatigue, anxiety and irritability.

General dosing should be in the 600 to 800 mg range. However, for GI cramping, asthma, constipation and heart disease, it is recommended to take magnesium to bowel tolerance (until the bowel movements become “loose”). For nocturnal leg cramps, kidney stone prevention and eclampsia, magnesium should be paired with 50 to 100 mg of vitamin B6.

Toxicity of magnesium is fairly low, with diarrhea being the biggest problem. Reduce the dose until bowel movements return to normal to prevent other possible symptoms of magnesium toxicity, such as calcium deficiency, hypotension, depletion of potassium and respiratory depression.31 Once a maintenance dose is established, calcium should be taken along with magnesium, in a 2:1 ratio.

For DCs treating acute muscle spasms, magnesium supplementation is a critical and often overlooked intervention. With the addition of magnesium supplementation to treatment protocols for myospasm, improved outcomes can be anticipated. 

Emmett J. Hughes, DC, MS, is associate professor of basic science at the University of Bridgeport College of Chiropractic. Since 1997, he has taught physiology, microscopic anatomy and physiology, clinical nutrition and soft-tissue technique. Dr. Hughes also maintains a private practice in Huntington, N.Y.   

1. Jung DW, Brierley GP. Matrix magnesium and the permeability of heart mitochondria to potassium ion. J Biol Chem 1986;261:6408-6415.
2. King DE, Mainous AG, et al. Dietary magnesium and C-reactive protein levels. J Amer Col Nutrition 2005;24:166-171.
3. Subar AF, Krebs-Smith SM. Dietary sources of nutrients among US adults, 1989 to 1991. J Amer Dietetic Assoc 1998;98:537-547.
4. Ford ES, Mokdad AH. Dietary magnesium intake in a national sample of U.S. adults. J Nutr 2003;133: 2879-2882.
5. Turlapaty PD, Altura BM. Magnesium deficiency produces spasms of coronary arteries: relationship to etiology of sudden death ischemic heart disease. Science 1980;208:198-200.
6. Caspi J, Rudis E, et al. Effects of magnesium on myocardial function after coronary artery bypass grafting. Ann Thorac Surg 1995;59:942-947.
7. Eisenberg MJ. Magnesium deficiency and sudden death. Am Heart J 1992;124: 544-9.
8. Rude RK, Singer FR. Magnesium deficiency and excess. Ann Rev Med 1981;32: 245-59.
9. Ralston MA, Murnane MR, et al. Magnesium content of serum, circulating mononuclear cells, skeletal muscle, and myocardium in congestive heart failure. Circulation 1989;80:573-580.
10. Newhouse IJ, Johnson KP, et al. Variability within individuals of plasma ionic magnesium concentrations. BMC Physiology 2002;2: 6-13.
11. Brannan PG, Vergne-Marini P, et al. Magnesium absorption in the human small intestine. Results in normal subjects, patients with chronic renal disease, and patients with absorptive hypercalciuria. J Clin Invest 1976; 57:1412-1418.
12. Osteoporosis:  The role of micronutrients. J Clin Nutr 2005;81:12325-12395.
13. Murphy E, Freudrich CC, Lieberman M. Cellular magnesium and Na/Mg exchange in heart cells. Ann Rev Physiol 1991; 53:273-87.
14. Shechter M, Sharir M, et al. Oral magnesium therapy improves endothelial function in patients with coronary artery disease. Circulation 2000;102: 2353-2358.
15. Maier JA, Malpuech-Bruegère C, et al. Low magnesium promotes endothelial cell dysfunction: implications for atherosclerosis, inflammation and thrombosis. Biochimica et Biophysica Acta, Molecular Basis of Disease 2004;1689:13-21.
16. Galland L. Magnesium and immune function: an overview. Magnesium 1988;7: 290-9.
17. Wolf FI and Cittadini A. Magnesium in cell proliferation and differentiation. Frontiers in Bioscience 1999; 4:607-617.
18. Reid JD, Hunter CN. Current understanding of the function of magnesium chelatase. Biochemical Society Transactions 2002;643-645.
19. Thung-Shenq L, Slaughter TF, et al. Regulation of human tissue tranglutaminase function by magnesium nucleotide complexes. J Biol Chem 1998;273:1776-1781.
20. Subar AF, Krebs-Smith AM, et al. Dietary sources of nutrients among US children 1989-1991. Pediatrics 1998;102:913-923.
21. Rassmussen HH, Mortensen PB, Jensen IW. Depression and magnesium deficiency. Int J Psychiatry Med 1989;19: 57-63.
22. Morris ME. Brain and CSF magnesium concentrations during magnesium deficit in animals and humans:  neurological symptoms. Magnes Res 1992;5:303-13.
23. Iseri LT, Freed J, Bures AR. Magnesium deficiency and cardiac disorders. Am J Med 1975;58:837-46.
24. Al-Ghamdi SM, Cameron EC, Sutton RA. Magnesium deficiency: pathophysiologic and clinical overview. Am J Kidney Dis 1994;24:737-52.
25. Rude RK. Magnesium deficiency and diabetes mellitus: Causes and effects. Postgrad Med 1992; 92: 222-4.
26. Whang R, Whang DD, Ryan MP. Refractory potassium repletion:  A consequence of magnesium deficiency. Arch Intern Med 1992;152:40-45.
27. Flink EB. Magnesium deficiency: Etiology and clinical spectrum. Acta Medica Scandinavica 1998;209:125-137.
28.  Rink EB. Magnesium deficiency in alcoholism. Alcoholism: Clinical and Experimental Res 1986;10:590-594.
29. Hogue CW, Hyder ML. Atrial fibrillation after cardiac operation: risks, mechanisms, and treatment. Ann Thoracic Surgery 2000;69:300-6.
30. Miller S, Crystal E, Garfinkle M, et al. Effects of magnesium on atrial fibrillation after cardiac surgery: A meta-analysis. Heart 2005;91:618-623.
31. Fassler CA, Rodriguez RM, Badesch DB, et al. Manesium toxicity as a cause of hypotension and hypoventilation. Archives Intern Med 1985;145:1604-1606.