Magnesium is the fourth most abundant mineral in the body and is essential to good health. Approximately 50% of the magnesium in your body magnesium is in your bones. The other half is found predominantly inside your tissue and organ cells. Only 1% of magnesium is found in your blood, but your body works very hard to keep blood levels of magnesium constant. Magnesium is absorbed in your small intestine, and is excreted through your kidneys.
You need magnesium for more than 300 enzymes that regulate biochemical reactions in your body. These enzymes include those involved in the secretion of glucose and insulin. Magnesium helps maintain normal muscle and nerve function, keeps your heart rhythm steady, supports a healthy immune system, and keeps your bones strong. Magnesium also helps regulate blood sugar levels, so it lowers the risk of type 2 diabetes. It also promotes normal blood pressure, which reduces the risk of stroke and heart disease. Magnesium is also involved in energy metabolism and protein synthesis.
Magnesium balances the effects of calcium on nerves and muscles, which helps to relax them. Inadequate magnesium in the diet allows calcium free entry into nerve cells. They become over-activated and cause excessive contractions. This results in muscle cramps, high blood pressure, migraine headaches, and fatigue. Magnesium is a calcium channel blocker. When enough magnesium is around, veins and arteries relax, which lessens resistance, lowers blood pressure, and improves the flow of blood, oxygen, and nutrients throughout the body. A deficiency of magnesium is associated with heart attack, and immediately following a heart attack, lack of sufficient magnesium promotes free radical injury to the heart. Magnesium, together with calcium, promotes healthy bones and helps to give them proper structure.
Green leafy 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 the following table:
|Pumpkin seeds, raw, 1 ounce||168||42|
|Nori, dried, 50 grams||150||37|
|Brazil nuts, unblanched, 1 ounce||107||27|
|Chia seeds, 1 ounce||95||24|
|Wheat Bran, crude, ¼ cup||89||22|
|Almonds, dry roasted, 1 ounce||80||20|
|Spinach, frozen, cooked, ½ cup||78||20|
|Raisin bran cereal, 1 cup||77||19|
|Chard, cooked, 1/2 cup||75||19|
|Cashews, dry roasted, 1 ounce||74||19|
|Soybeans, mature, cooked, ½ cup||74||19|
|Wheat germ, crude, ¼ cup||69||17|
|Nuts, mixed, dry roasted, 1 ounce||64||16|
|Bran flakes cereal, ¾ cup||64||16|
|Shredded wheat cereal, 2 rectangular biscuits||61||15|
|Oatmeal, instant, fortified, prepared w/ water, 1 cup||61||15|
|Peanuts, dry roasted, 1 ounce||50||13|
|Peanut butter, smooth, 2 Tablespoons||49||12|
|Potato, baked with skin, 1 medium||48||12|
|Blackeye peas, cooked, ½ cup||46||12|
|Pinto beans, cooked, ½ cup||43||11|
|Rice, brown, long-grained, cooked, ½ cup||42||11|
|Kidney beans, mature seeds, cooked, ½ cup||37||9|
|Lentils, mature seeds, cooked, ½ cup||36||9|
|Vegetarian baked beans, ½ cup||35||9|
|Kidney beans, canned, ½ cup||35||9|
|Pistachios, raw, 1 ounce||34||9|
|Banana, raw, 1 medium||32||8|
|Sesame seeds, raw, 1 tablespoon||32||8|
|Flax seeds, ground, 1 tablespoon||27||7|
|Cocoa, unsweetened, 1 tablespoon||27||7|
|Raisins, seedless, ½ cup packed||26||7|
|Bread, whole-wheat, commercially prepared, 1 slice||23||6|
|Avocado, cubes, ½ cup||22||6|
|Cumin seed, 1 tablespoon||22||6|
|Tomato, raw, 1 large||20||5|
*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.
Even though many Americans do not get recommended amounts of magnesium, symptoms of magnesium deficiency are rarely seen in the US. However, there is concern that many people may not have enough body stores of magnesium because dietary intake may not be high enough. Having enough body stores of magnesium may be protective against disorders such as cardiovascular disease and immune dysfunction.
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. Gastrointestinal disorders that impair absorption, such as such as Crohn’s disease, gluten sensitive enteropathy, regional enteritis, and intestinal surgery can limit the body’s ability to absorb magnesium. Chronic or excessive vomiting and diarrhea may also result in magnesium depletion.
Healthy kidneys are able to limit urinary excretion of magnesium to make up for low dietary intake. However, excessive loss of magnesium in urine can be a side effect of some medications, including certain diuretics, antibiotics, and medications used to treat cancer (anti-neoplastic medication). Examples of these medications are:
- Diuretics: Lasix, Bumex, Edecrin, and hydrochlorothiazide
- Antibiotics: Gentamicin, and Amphotericin
- Anti-neoplastic medication: Cisplatin
Magnesium deficiency can also occur in cases of poorly-controlled diabetes and alcohol abuse. Low blood levels of magnesium occur in 30% to 60% of alcoholics, and in nearly 90% of patients experiencing alcohol withdrawal. Anyone who substitutes alcohol for food will usually have significantly lower magnesium intakes.
Older adults are at increased risk for magnesium deficiency, because they have lower dietary intakes of magnesium than younger adults. In addition, magnesium absorption decreases and renal excretion of magnesium increases in older adults. 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. It is very important for older adults to get recommended amounts of dietary magnesium.
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 (sudden changes in behaviors caused by excessive electrical activity in the brain), personality changes, abnormal heart rhythms, and coronary spasms. 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).
Eating a variety of whole grains, legumes, and vegetables (especially dark-green, leafy vegetables) every day will help provide recommended intakes of magnesium and maintain normal storage levels of this mineral. Increasing dietary intake of magnesium can often restore mildly depleted magnesium levels.
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