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Magnesium



RDI Food Sources Deficiencies Supplements Health Risks Current Issues

[ Please see the introductory essay on minerals for important information.]



National Institutes of Health
 Warren Grant Magnuson Clinical Center

      Magnesium is a mineral needed by every cell of your body. About half of your body's magnesium stores are found inside cells of body tissues and organs, and half are combined with calcium and phosphorus in bone. Only 1 percent of the magnesium in your body is found in blood. Your body works very hard to keep blood levels of magnesium constant.
      Magnesium is needed for more than 300 biochemical reactions in the body. It helps maintain normal muscle and nerve function, keeps heart rhythm steady, and bones strong. It is also involved in energy metabolism and protein synthesis.

      The current RDI for magnesium used by the FDA is 400 mg. The most recent assessment for this nutrient from the National Academy of Sciences (NAS) is detailed in the table below. The Tolerable Upper Intake Level (UL) for magnesium represents intake from pharmacological agents only, and does not include intake from food and water.

Reference Values for Magnesium
Current RDI1 is 400 mg
  Age
(years)
RDA2
(mg)
DRI3
RDA (mg)         UL4 (mg)
 Children 1- 3   80       80       65      
  4- 6   120          
  4- 8     130       110      
  7-10   170          
 Males 9-13     240       350      
  14-18     410       350      
  11-14   270          
  15-18   400          
  19-30   350       400       350      
  31+     350       420       350      
 Females 9-13     240       350      
  14-18     360       350      
  11-14   280          
  15-18   300          
  19-30   280       310       350      
  31+     280       320       350      
  pregnant 18-     320       400       350      
  19-30   320       350       350      
  31+     320       360       350      
  lactating 1st 6 mo    355          
  2nd 6 mo    340          
  18-       360       350      
  19-30     310       350      
  31+       320       350      
  1.  Reference Daily Intake referenced on current food labels [Title 21 CFR]
  2.  Recommended Dietary Allowances  [NAS RDAs 10th ed, 1989]
  3.  Dietary Reference Intakes
         (RDAs and tolerable Upper intake Levels from recent NAS DRI Study
  4.  Intake from pharmacological agents only; not including intake from
         food and water.
Updated: Sep 2000   
Abbreviations, Units and Measurements

      Results of two national surveys, the National Health and Nutrition Examination Survey (NHANES III-1988-91) and the Continuing Survey of Food Intakes of Individuals (1994 CSFII), indicated that the diets of most adult men and women do not provide the recommended amounts of magnesium. The surveys also suggested that adults age 70 and over eat less magnesium than younger adults, and that non-Hispanic black subjects consumed less magnesium than either non-Hispanic white or Hispanic subjects.


 Food Sources
      Green vegetables such as spinach provide magnesium because the center of the chlorophyll molecule contains magnesium. Nuts, seeds, and some whole grains are also good sources of magnesium.
      Although magnesium is present in many foods, it usually occurs in small amounts. As with most nutrients, daily needs for magnesium cannot be met from a single food. Eating a wide variety of foods, including five servings of fruits and vegetables daily and plenty of whole grains, helps to ensure an adequate intake of magnesium.
      The magnesium content of refined foods is usually low. Whole-wheat bread, for example, has twice as much magnesium as white bread because the magnesium-rich germ and bran are removed when white flour is processed.
      Water can provide magnesium, but the amount varies according to the water supply. "Hard" water contains more magnesium than "soft" water. Dietary surveys do not estimate magnesium intake from water, which may lead to underestimating total magnesium intake and its variability.


 Deficiencies
      Even though dietary surveys suggest that many Americans do not consume magnesium in recommended amounts, magnesium deficiency is rarely seen in the United States in adults. When magnesium deficiency does occur, it is usually due to excessive loss of magnesium in urine, gastrointestinal system disorders that cause a loss of magnesium or limit magnesium absorption, or a chronically low intake of magnesium.
      Treatment with diuretics (water pills), some antibiotics, and some medicine used to treat cancer, such as Cisplatin, can increase the loss of magnesium in urine. Poorly controlled diabetes increases loss of magnesium in urine, causing a depletion of magnesium stores. Alcohol also increases excretion of magnesium in urine, and a high alcohol intake has been associated with magnesium deficiency.
      Gastrointestinal problems, such as malabsorption disorders, can cause magnesium depletion by preventing the body from using the magnesium in food. Chronic or excessive vomiting and diarrhea may also result in magnesium depletion.
      Signs of magnesium deficiency include confusion, disorientation, loss of appetite, depression, muscle contractions and cramps, tingling, numbness, abnormal heart rhythms, coronary spasm, and seizures.

 Supplements
      Healthy adults who eat a varied diet do not generally need to take a magnesium supplement. Magnesium supplementation is usually indicated when a specific health problem or condition causes an excessive loss of magnesium or limits magnesium absorption.
      Extra magnesium may be required by individuals with conditions that cause excessive urinary loss of magnesium, chronic malabsorption, severe diarrhea and steatorrhea, and chronic or severe vomiting.
      Loop and thiazide diuretics, such as Lasix, Bumex, Edecrin, and Hydrochlorothiazide, can increase loss of magnesium in urine. Medicines such as Cisplatin, which is widely used to treat cancer, and the antibiotics Gentamicin, Amphotericin, and Cyclosporin also cause the kidneys to excrete (lose) more magnesium in urine. Doctors routinely monitor magnesium levels of individuals who take these medicines and prescribe magnesium supplements if indicated.
      Poorly controlled diabetes increases loss of magnesium in urine and may increase an individual's need for magnesium. A medical doctor would determine the need for extra magnesium in this situation. Routine supplementation with magnesium is not indicated for individuals with well-controlled diabetes.
      People who abuse alcohol are at high risk for magnesium deficiency because alcohol increases urinary excretion of magnesium. Low blood levels of magnesium occur in 30 percent to 60 percent of alcoholics, and in nearly 90 percent of patients experiencing alcohol withdrawal. In addition, alcoholics who substitute alcohol for food will usually have lower magnesium intakes. Medical doctors routinely evaluate the need for extra magnesium in this population.
      The loss of magnesium through diarrhea and fat malabsorption usually occurs after intestinal surgery or infection, but it can occur with chronic malabsorptive problems such as Crohn's disease, gluten sensitive enteropathy, and regional enteritis. Individuals with these conditions may need extra magnesium. The most common symptom of fat malabsorption, or steatorrhea, is passing greasy, offensive-smelling stools.
      Occasional vomiting should not cause an excessive loss of magnesium, but conditions that cause frequent or severe vomiting may result in a loss of magnesium large enough to require supplementation. In these situations, your medical doctor would determine the need for a magnesium supplement.
      Individuals with chronically low blood levels of potassium and calcium may have an underlying problem with magnesium deficiency. Adding magnesium supplements to their diets may make potassium and calcium supplementation more effective for them. Doctors routinely evaluate magnesium status when potassium and calcium levels are abnormal, and prescribe a magnesium supplement when indicated.
      Doctors will measure blood levels of magnesium whenever a magnesium deficiency is suspected. When levels are mildly depleted, increasing dietary intake of magnesium can help restore blood levels to normal. Eating at least five servings of fruits and vegetables daily, and choosing dark-green leafy vegetables often, as recommended by the Dietary Guidelines for Americans, the Food Guide Pyramid, and the Five-a-Day program, will help adults at-risk of having a magnesium deficiency consume recommended amounts of magnesium. When blood levels of magnesium are very low, an intravenous drip (IV drip) may be needed to return levels to normal. Magnesium tablets also may be prescribed, but some forms, in particular magnesium salts, can cause diarrhea. Your medical doctor or qualified health-care provider can recommend the best way to get extra magnesium when it is needed.

 Health Risks
      Dietary magnesium does not pose a health risk, however very high doses of magnesium supplements, which may be added to laxatives, can promote adverse effects such as diarrhea. Magnesium toxicity is more often associated with kidney failure, when the kidney loses the ability to remove excess magnesium. Very large doses of laxatives also have been associated with magnesium toxicity, even with normal kidney function. The elderly are at risk of magnesium toxicity because kidney function declines with age and they are more likely to take magnesium-containing laxatives and antacids.
      Signs of excess magnesium can be similar to magnesium deficiency and include mental status changes, nausea, diarrhea, appetite loss, muscle weakness, difficulty breathing, extremely low blood pressure, and irregular heartbeat.
      The Institute of Medicine of the National Academy of Sciences has established a tolerable upper intake level (UL) for supplementary magnesium for adolescents and adults at 350 mg daily. As intake increases above the UL, the risk of adverse effects increases.

 Current Issues
      Blood pressure. Evidence suggests that magnesium may play an important role in regulating blood pressure. Diets that provide plenty of fruits and vegetables, which are good sources of potassium and magnesium, are consistently associated with lower blood pressure. The DASH study (Dietary Approaches to Stop Hypertension) suggested that high blood pressure could be significantly lowered by a diet high in magnesium, potassium, and calcium, and low in sodium and fat. In another study, the effect of various nutritional factors on incidence of high blood pressure was examined in over 30,000 U.S. male health professionals. After four years of follow-up, it was found that a greater magnesium intake was significantly associated with a lower risk of hypertension. The evidence is strong enough that 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 for preventing and managing high blood pressure.
      Heart disease. Magnesium deficiency can cause metabolic changes that may contribute to heart attacks and strokes. There is also evidence that low body stores of magnesium increase the risk of abnormal heart rhythms, which may increase the risk of complications associated with a heart attack. Population surveys have associated higher blood levels of magnesium with lower risk of coronary heart disease. In addition, dietary surveys have suggested that a higher magnesium intake is associated with a lower risk of stroke. Further studies are needed to understand the complex relationships between dietary magnesium intake, indicators of magnesium status, and heart disease.
      Osteoporosis. Magnesium deficiency may be a risk factor for postmenopausal osteoporosis. This may be due to the fact that magnesium deficiency alters calcium metabolism and the hormone that regulates calcium. Several studies have suggested that magnesium supplementation may improve bone mineral density, but researchers believe that further investigation on the role of magnesium in bone metabolism and osteoporosis is needed.
      Diabetes. Magnesium is important to carbohydrate metabolism. It may influence the release and activity of insulin, the hormone that helps control blood glucose levels. Elevated blood glucose levels increase the loss of magnesium in the urine, which in turn lowers blood levels of magnesium. This explains why low blood levels of magnesium (hypomagnesemia) are seen in poorly controlled type 1 and type 2 diabetes.
      In 1992, the American Diabetes Association issued a consensus statement that concluded: "Adequate dietary magnesium intake can generally be achieved by a nutritionally balanced meal plan as recommended by the American Diabetes Association." It recommended that "... only diabetic patients at high risk of hypomagnesemia should have total serum (blood) magnesium assessed, and such levels should be repleted (replaced) only if hypomagnesemia can be demonstrated."

The text in this article was prepared by the Warren Grant Magnuson Clinical Center. Revisions to this article, and the Reference Daily Intake section (including the Reference Values table) were prepared by Preventive Health Today.

Updated September 2000

Warren Grant Magnuson Clinical Center
National Institutes of Health
Bethesda, Maryland
 




 

 

 

 

 

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