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
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. 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.
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. Refined grains are generally low in magnesium. 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.
Table 1: Selected food sources of magnesium
| 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, ½ 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, ½ 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). Most food labels do not list a food’s magnesium content. The percent DV (%DV) listed on the table above indicates the percentage of the DV provided in one serving. A food providing 5% of the DV or less per serving is a low source while a food that provides 10-19% of the DV is a good source. A food that provides 20% or more of the DV is high in that nutrient. It is important to remember that foods that provide lower percentages of the DV also contribute to a healthful diet. For foods not listed in this table, please refer to the U.S. Department of Agriculture’s Nutrient Database Web site.
What are the Dietary Reference Intakes for magnesium?
Recommendations for magnesium are provided in the Dietary Reference Intakes (DRIs) developed by the Institute of Medicine of the National Academy of Sciences. Dietary Reference Intakes is the general term for a set of reference values used for planning and assessing nutrient intake for healthy people. Three important types of reference values included in the DRIs are Recommended Dietary Allowances (RDA), Adequate Intakes(AI), and Tolerable Upper Intake Levels (UL). The RDA recommends the average daily intake that is sufficient to meet the nutrient requirements of nearly all (97%-98%) healthy people. An AI is set when there is insufficient scientific data available to establish a RDA for specific age/gender groups. AIs meet or exceed the amount needed to maintain a nutritional state of adequacy in nearly all members of a specific age and gender group. The UL, on the other hand, is the maximum daily intake unlikely to result in adverse health effects. Table 2 lists the RDAs for magnesium, in milligrams, for children and adults.
Table 2: Recommended Dietary Allowances for magnesium for children and adults
| Age (years) |
Male (mg/day) |
Female (mg/day) |
Pregnancy (mg/day) |
Lactation (mg/day) |
|---|---|---|---|---|
| 1-3 | 80 | 80 | N/A | N/A |
| 4-8 | 130 | 130 | N/A | N/A |
| 9-13 | 240 | 240 | N/A | N/A |
| 14-18 | 410 | 360 | 400 | 360 |
| 19-30 | 400 | 310 | 350 | 310 |
| 31+ | 420 | 320 | 360 | 320 |
There is insufficient information on magnesium to establish a RDA for infants. For infants 0 to 12 months, the DRI is in the form of an Adequate Intake (AI), which is the mean intake of magnesium in healthy, breastfed infants. Table 3 lists the AIs for infants in milligrams (mg).
Table 3: Recommended Adequate Intake for magnesium for infants
| Age (months) |
Males and Females (mg/day) |
|---|---|
| 0 to 6 | 30 |
| 7 to 12 | 75 |
Data from the 1999-2000 National Health and Nutrition Examination Survey suggest that substantial numbers of adults in the United States (US) fail to get recommended amounts of magnesium in their diets. Among adult men and women, the diets of Caucasians have significantly more magnesium than do those of African-Americans. Magnesium intake is lower among older adults in every racial and ethnic group. Among African-American men and Caucasian men and women who take dietary supplements, the intake of magnesium is significantly higher than in those who do not.