Potential Health Benefits of the Mineral Magnesium
Magnesium has never been a nutritional superstar, but in recent years research has confirmed its many crucial roles in the body and uncovered new potential benefits. Notably, the mineral's involved in energy production, cell growth, blood pressure, bone health and the functioning of the heart, nerves and muscles. While there's no doubt that magnesium-rich foods are some of the best choices around, supplements are another matter.
Heart Health, Blood Pressure and Magnesium
Insufficient magnesium intake increases cardiovascular risk. Magnesium is essential for the activity of the heart muscle and the nerves that initiate the heartbeat, and it helps regulate blood pressure. An adequate intake helps prevent arrhythmias, reduce cardiac damage from oxidative stress, keep blood vessels healthy, prevent spasms of coronary arteries that can cause angina, and boost HDL ("good") cholesterol levels. So it makes sense that many observational studies have found that people with a high dietary intake of magnesium have a lower risk of heart disease and stroke—and that people who live in areas with hard water (which is high in magnesium) have a lower coronary death rate.
But while several clinical trials have found that people with certain heart problems, coronary heart diseas,e or hypertension may benefit from increased magnesium intake (sometimes from food, sometimes from supplements or injections), others have not. Overall, studies on magnesium supplements for heart health or blood pressure control have had inconsistent results.
Magnesium-rich foods are a big part of the anti-hypertension DASH diet. However, foods rich in magnesium are also rich in other heart-healthy nutrients (such as potassium) and fiber, so it's hard to separate out the effect of this single mineral.
Diabetes and Magnesium
Magnesium is also essential for the body's use of insulin and the burning of carbohydrates. Observational studies have linked low magnesium levels to increased risk of diabetes and insulin resistance (which often leads to type 2 diabetes) as well as poor blood sugar control in people with the disease. Several small studies of magnesium supplements in people with diabetes have had positive results. Research is continuing.
Bone Health and Magnesium
Working closely with calcium and vitamin D, magnesium helps form and maintain bones and teeth. Researchers have found that people with high magnesium intakes have greater bone density, and that women with osteoporosis tend to have low magnesium levels. But it's not known if supplements make a difference. The studies that have shown that supplemental calcium and/or vitamin D reduce the risk of fractures have not included magnesium. While a magnesium deficiency can impair the use of calcium and vitamin D, doubling or tripling an adequate magnesium intake does not increase calcium absorption.
Colon Cancer and Magnesium
Several studies have found that people who consume the most magnesium from food are less likely to develop colon cancer and perhaps rectal cancer. The studies did not involve supplements, however.
Migraines and Magnesium
Researchers have found that people with migraines tend to have low brain magnesium levels during an attack and are more likely to have low magnesium overall. Two studies from the 1990s found that supplements help reduce the frequency of attacks, though one did not.
How Much Magnesium You Need
Most Americans don't consume the recommended daily intake of magnesium, which is 320 milligrams a day for women, 420 for men. Older people often have low levels because they tend to consume and absorb less of the mineral. Since there's no good way to measure total magnesium in the body, however, it's hard to know exactly how many people are truly deficient.
Because magnesium plays so many roles, the symptoms of deficiency can vary widely. Many symptoms involve changes in nerve and muscle function, such as muscle weakness, cramps and spasms. Cardiac symptoms include arrhythmias. Poor blood sugar control, elevated blood pressure and nausea may also result.
Bottom line: Eat foods rich in magnesium—whole grains, nuts, beans, seeds, fish, avocados and leafy greens such as spinach—which happen to be among the most nutritious foods. About 80 percent of the magnesium in grains is in the bran and germ, which are removed in milling, so refined grain products (such as white bread and white rice) are poor sources. If your drinking water is hard, you'll get a fair amount of magnesium from it.
For older people, or anyone not eating a balanced diet, a basic multivitamin/mineral is a good way to get supplemental magnesium (usually 50 to 100 milligrams). Some calcium supplements also contain magnesium.
Don't take a separate magnesium supplement unless you're at high risk for a deficiency because you drink heavily, have uncontrolled diabetes or take a medication (such as a proton pump inhibitor for reflux disease) or have a disorder (such as Crohn's disease) that can affect absorption. But talk with your doctor first. You can't get too much magnesium from food. In contrast, supplements and excessive use of certain magnesium-containing antacids or laxatives can cause diarrhea, nausea and cramps. People with kidney disease are at risk for more serious problems from excess magnesium.
Amount of Magnesium in Common Foods (milligrams)
Halibut or mackerel, cooked, 4 oz—120 mg
Sunflower seeds, dried, 1 oz—100 mg
Spinach/chard, cooked, 1/2 cup—80 mg
Almonds or cashews, 1 oz—77 mg
Flounder or sole, cooked, 4 oz—75 mg
Wheat germ, 1 oz—70 mg
Beans, cooked, 1/2 cup—50 mg
Oatmeal, cooked, 1 cup—55 mg
Peanuts, 1 oz—50 mg
Potato, baked with skin, medium—50 mg
Tofu, 3 oz—50 mg
Avocado, 4 oz—50 mg
Yogurt, plain, 1 cup—45 mg
Corn kernels, cooked, 1 cup—45 mg
Pasta, whole-wheat, cooked, 1 cup—42 mg
Rice, brown, cooked, 1/2 cup—40 mg
Dark chocolate, 1 oz—30 mg
Milk, 1 cup—25 mg
Bread, whole-wheat, 1 slice—25 mg
Source: Originally published in The University of California, Berkeley Wellness Letter (July 2011