Magnesium Requirement

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% is found in the 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.

Causes and Development

Treatment with diuretics (water pills), some antibiotics, and some cancer medicines 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.

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.  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.

Many people do not get enough magnesium from their diet for reasons including the following:

• The amount of magnesium in the soil in which the food is grown may be reduced.
• Magnesium can be lost in the processing and refining of foods and in making oils from the magnesium-rich nuts and seeds.  Nearly 85% of the magnesium in grains is lost during the milling of flours.
• Soaking and boiling foods can leach magnesium into the water, so the "pot liquor" from cooking vegetables may be high in magnesium and other minerals.
• Oxalic acid in vegetables such as rhubarb, spinach and chard, and phytic acid in some grains may form insoluble salts with magnesium, causing it to be eliminated rather than absorbed.
• Supplemental vitamin D or calcium reduces magnesium uptake.
• Diets high in phosphorus (meat, milk products, lentils, seeds, beans, nuts, chocolate, peanut butter, bran) reduce magnesium uptake.
• Magnesium elimination is increased in people who use alcohol, caffeine or excess sugar, or who take diuretics or birth control pills.
• Magnesium is absorbed toward the end of the small intestine.  If any portion of this area (called the ileum) has been removed, magnesium absorption will be reduced.

Signs and Symptoms

Signs of magnesium deficiency include confusion, disorientation, loss of appetite, depression, muscle contractions and cramps, tingling, numbness, abnormal heart rhythms, coronary spasm, and seizures.

Diagnosis and Tests

Doctors will measure blood levels of magnesium whenever a magnesium deficiency is suspected.

While magnesium deficiency is fairly common, it is frequently overlooked as a source of problems.  The reason is that serum magnesium levels (the test most doctors use) do not reflect actual body stores of magnesium.  Blood levels are kept within the normal range at the expense of other tissues.  When 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 and Prevention

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.

What is the health risk of too much magnesium?
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.

Complications

Magnesium and 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.

Magnesium and 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.

Magnesium and 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.

Magnesium and 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".