Magnesium: What is it?
Magnesium is the fourth most abundant mineral in the body and is essential to good health. Approximately 50% of total body magnesium is found in bone. The other half is found predominantly inside cells of body tissues and organs. Only 1% of magnesium is found in blood, but the body works very hard to keep blood levels of magnesium constant [1].
Magnesium is needed for more than 300 biochemical reactions in the body. It helps maintain normal muscle and nerve function, keeps heart rhythm steady, supports a healthy immune system, and keeps bones strong. Magnesium also helps regulate blood sugar levels, promotes normal blood pressure, and is known to be involved in energy metabolism and protein synthesis [2-3]. There is an increased interest in the role of magnesium in preventing and managing disorders such as hypertension, cardiovascular disease, and diabetes. Dietary magnesium is absorbed in the small intestines. Magnesium is excreted through the kidneys [1-3,4].
What foods provide magnesium?
Green vegetables such as spinach are good sources of magnesium because the center of the chlorophyll molecule (which gives green vegetables their color) contains magnesium. Some legumes (beans and peas), nuts and seeds, and whole, unrefined grains are also good sources of magnesium [5]. Refined grains are generally low in magnesium [4-5]. When white flour is refined and processed, the magnesium-rich germ and bran are removed. Bread made from whole grain wheat flour provides more magnesium than bread made from white refined flour. Tap water can be a source of magnesium, but the amount varies according to the water supply. Water that naturally contains more minerals is described as "hard". "Hard" water contains more magnesium than "soft" water.
Eating a wide variety of legumes, nuts, whole grains, and vegetables will help you meet your daily dietary need for magnesium. Selected food sources of magnesium are listed in Table 1.
| FOOD | Milligrams (mg) | %DV* |
|---|---|---|
| Halibut, cooked, 3 ounces | 90 | 20 |
| Almonds, dry roasted, 1 ounce | 80 | 20 |
| Cashews, dry roasted, 1 ounce | 75 | 20 |
| Soybeans, mature, cooked, ½ cup | 75 | 20 |
| Spinach, frozen, cooked, ½ cup | 75 | 20 |
| Nuts, mixed, dry roasted, 1 ounce | 65 | 15 |
| Cereal, shredded wheat, 2 rectangular biscuits | 55 | 15 |
| Oatmeal, instant, fortified, prepared w/ water, 1 cup | 55 | 15 |
| Potato, baked w/ skin, 1 medium | 50 | 15 |
| Peanuts, dry roasted, 1 ounce | 50 | 15 |
| Peanut butter, smooth, 2 Tablespoons | 50 | 15 |
| Wheat Bran, crude, 2 Tablespoons | 45 | 10 |
| Blackeyed Peas, cooked, ½ cup | 45 | 10 |
| Yogurt, plain, skim milk, 8 fluid ounces | 45 | 10 |
| Bran Flakes, ¾ cup | 40 | 10 |
| Vegetarian Baked Beans, ½ cup | 40 | 10 |
| Rice, brown, long-grained, cooked, ½ cup | 40 | 10 |
| Lentils, mature seeds, cooked, ½ cup | 35 | 8 |
| Avocado, California, ½ cup pureed | 35 | 8 |
| Kidney Beans, canned, ½ cup | 35 | 8 |
| Pinto Beans, cooked, ½ cup | 35 | 8 |
| Wheat Germ, crude, 2 Tablespoons | 35 | 8 |
| Chocolate milk, 1 cup | 33 | 8 |
| Banana, raw, 1 medium | 30 | 8 |
| Milk Chocolate candy bar, 1.5 ounce bar | 28 | 8 |
| Milk, reduced fat (2%) or fat free, 1 cup | 27 | 8 |
| Bread, whole wheat, commercially prepared, 1 slice | 25 | 6 |
| Raisins, seedless, ¼ cup packed | 25 | 6 |
| Whole Milk, 1 cup | 24 | 6 |
| Chocolate Pudding, 4 ounce ready-to-eat portion | 24 | 6 |
*DV = Daily Value. DVs are reference numbers developed by the Food and Drug Administration (FDA) to help consumers determine if a food contains a lot or a little of a specific nutrient. The DV for magnesium is 400 milligrams (mg).
When can magnesium deficiency occur?
Even though dietary surveys suggest that many Americans do not consume recommended amounts of magnesium, symptoms of magnesium deficiency are rarely seen in the US. However, there is concern about the prevalence of sub-optimal magnesium stores in the body. For many people, dietary intake may not be high enough to promote an optimal magnesium status, which may be protective against disorders such as cardiovascular disease and immune dysfunction [7-8].
The health status of the digestive system and the kidneys significantly influence magnesium status. Magnesium is absorbed in the intestines and then transported through the blood to cells and tissues. Approximately one-third to one-half of dietary magnesium is absorbed into the body [9-10]. Gastrointestinal disorders that impair absorption such as Crohn's disease can limit the body's ability to absorb magnesium. These disorders can deplete the body's stores of magnesium and in extreme cases may result in magnesium deficiency. Chronic or excessive vomiting and diarrhea may also result in magnesium depletion [1,10].
Healthy kidneys are able to limit urinary excretion of magnesium to compensate for low dietary intake. However, excessive loss of magnesium in urine can be a side effect of some medications and can also occur in cases of poorly-controlled diabetes and alcohol abuse [11-18].
Early signs of magnesium deficiency include loss of appetite, nausea, vomiting, fatigue, and weakness. As magnesium deficiency worsens, numbness, tingling, muscle contractions and cramps, seizures, personality changes, abnormal heart rhythms, and coronary spasms can occur [1,3-4]. Severe magnesium deficiency can result in low levels of calcium in the blood (hypocalcemia). Magnesium deficiency is also associated with low levels of potassium in the blood (hypokalemia) [1,19-20].
Many of these symptoms are general and can result from a variety of medical conditions other than magnesium deficiency. It is important to have a physician evaluate health complaints and problems so that appropriate care can be given.
Who may need extra magnesium?
Magnesium supplementation may be indicated when a specific health problem or condition causes an excessive loss of magnesium or limits magnesium absorption [2,7,9-11].
Some medicines may result in magnesium deficiency, including certain diuretics, antibiotics, and medications used to treat cancer (anti-neoplastic medication) [12,14,19]. Examples of these medications are:
Diuretics: Lasix, Bumex, Edecrin, and hydrochlorothiazide
Antibiotics: Gentamicin, Amphotericin, and Cyclosporin
Anti-neoplastic medication: Cisplatin
Individuals with poorly-controlled diabetes may benefit from magnesium supplements because of increased magnesium loss in urine associated with hyperglycemia [21].
Magnesium supplementation may be indicated for persons with alcoholism. Low blood levels of magnesium occur in 30% to 60% of alcoholics, and in nearly 90% of patients experiencing alcohol withdrawal [17-18]. Anyone who substitutes alcohol for food will usually have significantly lower magnesium intakes.
Individuals with chronic malabsorptive problems such as Crohn's disease, gluten sensitive enteropathy, regional enteritis, and intestinal surgery may lose magnesium through diarrhea and fat malabsorption [22]. Individuals with these conditions may need supplemental magnesium.
Individuals with chronically low blood levels of potassium and calcium may have an underlying problem with magnesium deficiency. Magnesium supplements may help correct the potassium and calcium deficiencies [19].
Older adults are at increased risk for magnesium deficiency. The 1999-2000 and 1998-94 National Health and Nutrition Examination Surveys suggest that older adults have lower dietary intakes of magnesium than younger adults [6,23]. In addition, magnesium absorption decreases and renal excretion of magnesium increases in older adults [4]. Seniors are also more likely to be taking drugs that interact with magnesium. This combination of factors places older adults at risk for magnesium deficiency [4]. It is very important for older adults to consume recommended amounts of dietary magnesium.
Doctors can evaluate magnesium status when above-mentioned medical problems occur, and determine the need for magnesium supplementation.
Again, more on magnesium can be found here.
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