Magnesium

Magnesium (Mg) is an element belonging to the alkaline earth metal group. It participates in over 300 metabolic reactions, is crucial for life and health and is the fourth most common mineral in the body. In the body, it forms ions that have an electric charge of þ2. Humans must meet their needs for magnesium from their diet. Magnesium is found mainly in plants and in some drinking water.

Magnesium

SOURCE: Office of Dietary Supplements. National Institutes of Health. “Magnesium: Fact Sheet for Health Professionals.” U.S. Department of Health and Human Services. https://ods.od.nih.gov/factsheets/Magnesium-HealthProfessional (accessed April 23, 2018).

Magnesium is necessary for many cellular reactions critical to maintaining life. It plays a role in:

Magnesium is in chlorophyll, the pigment that makes plants green. Humans absorb magnesium from food as it passes through the small intestine. The kidneys normally regulate how much magnesium is in the blood, and any excess magnesium is excreted in urine. Magnesium levels can be measured with a blood test.

When magnesium dissolves in body fluids, it becomes an electrolyte. Electrolytes are ions that have an electric charge. Magnesium is a cation, or positively charged ion, with an electric charge of +2, meaning it has lost two of its negatively charged elections. Other important electrolytes in the body are sodium (Na⁺), potassium (K⁺), calcium (Ca²⁺), magnesium (Mg²⁺), chloride (Cl^-), phosphate (HPO4^2-), bicarbonate (HCO^3-), and sulfate (SO4^2-). Multiple electrolytes are involved in most metabolic reactions. These electrolytes are not evenly distributed within the body, and their electric charge and uneven distribution are what allow many chemical reactions to occur. About 50%– 60% of the 25 grams of magnesium in an adult's body is in the bones. About 25% is in muscle cells, 6%–7% in other cells, and less than 1% outside cells (e.g., in extracellular fluid or in blood serum).

Magnesium is involved in many reactions. One of the most important is in synthesizing adenosine triphosphate (ATP), the molecule that supplies most of the energy to drive cellular metabolism. Magnesium is also required to create new DNA, ribonucleic acid (RNA), and proteins. The electrical charge of the magnesium ion is important in regulating the transmission of nerve impulses, muscle contraction, and the movement of nutrients and other electrolytes in and out of cells. Magnesium also has an effect on the way calcium is deposited in bones. It makes bone structurally more dense and stronger.

Chlorophyll, the pigment that makes plants green, contains magnesium. Good natural sources of magnesium include dark green vegetables such as spinach and Swiss chard. Other vegetables high in magnesium are lima beans, black-eyed peas, almonds, cashew nuts, and peanuts. Whole grains contain a lot of magnesium, but processing removes most of it. Therefore brown rice is a good source of magnesium, but white rice is not. Whole wheat flour has more magnesium than white flour, and wheat bran and oat bran have more than either type of flour. Some water that is high in minerals (hard water) has a significant amount of magnesium; the amount varies widely depending on location. Magnesium is also found in many multivitamins and is available as a single-ingredient supplement. The amount of magnesium available to the body from dietary supplements varies depending on the molecule in which magnesium is found. Common forms of magnesium in dietary supplements include magnesium oxide, magnesium gluconate, magnesium citrate, and magnesium aspartate. Some antacids contain a significant amount of magnesium hydroxide. The best way to get an adequate amount of magnesium is to eat a healthy diet high in green vegetables and whole grains.

The following list gives the approximate magnesium content for some common foods:

Hypomagnesemia, or low levels of magnesium, are estimated to occur in about 2% of the American population, in 10%–20% of hospitalized patients, and in up to 60% of patients in intensive care. Anywhere between 30% and 80% of people with alcoholism have hypomagnesemia, as do about 25% of people with diabetes.

Magnesium deficiency can be caused either by insufficient intake or excessive excretion of magnesium. Causes of insufficient intake include digestive disorders that interfere with the absorption of magnesium (e.g., Crohn's disease, celiac disease, inflammatory bowel syndrome), malnutrition with a limited diet of green vegetables, alcoholism (alcohol is substituted for food), and anorexia nervosa (due to self-starvation). Some causes of excessive excretion of magnesium include kidney failure, diabetes, use of some diuretic drugs, and some hormone disorders of the parathyroid gland.

The U.S. Institute of Medicine (IOM) of the National Academy of Sciences has developed values called Dietary Reference Intakes (DRIs) for many vitamins and minerals. The DRIs consist of three sets of numbers: recommended dietary allowance (RDA), which defines the average daily amount of the nutrient needed to meet the health needs of 97%–98% of the population; adequate intake (AI), an estimate set when there is not enough information to determine an RDA; and tolerable upper intake level (UL), the average maximum amount that can be taken daily without risking negative side effects. The DRIs are calculated for children, adult men, adult women, pregnant women, and breastfeeding women.

The IOM has not set RDAs for magnesium in children under one year old because of incomplete scientific information. Instead, it has set AI levels for this age group. The RDAs for magnesium are the amount that has been determined to prevent deficiency.

However, based on recent findings about the relationship between magnesium, diabetes, and cardiovascular disease, there is some debate over whether this represents the optimum amount for health. RDAs and ULs for magnesium are measured in milligrams (mg). There are no ULs for magnesium that is obtained from food and water. All magnesium ULs apply to dietary supplements only.

The following list gives the daily RDAs and AIs and ULs for magnesium for healthy individuals as established by the IOM:

The kidneys are the main regulator of magnesium. People with kidney disease should not take magnesium supplements.

Pregnant women should discuss their magnesium needs with their healthcare provider. Many pregnant women have low levels of magnesium but should use supplements only under medical supervision. Low magnesium levels are thought to contribute to preeclampsia and eclampsia and possibly to increase the risk of early labor.

People undergoing surgery should tell their anesthesiologist if they are taking magnesium supplements, antacids, or laxatives because magnesium increases the muscle-relaxing effects of certain anesthetics.

Certain drugs and conditions can cause an excessive loss of magnesium. These include:

Certain drugs may be less effective when taken with magnesium supplements. These include some antibiotics, and digoxin, a heart medication. Iron may be absorbed more poorly in the presence of magnesium.

Some minerals decrease the absorption of magnesium. These include calcium, manganese, and phosphate. Boron appears to increase magnesium levels.

No complications are expected from magnesium obtained from food and water. Potential complications related to excess use of magnesium supplements or from inadequate levels of magnesium are discussed above.

The safety of magnesium supplements in children has not been investigated. Breastfeeding women should avoid magnesium supplements and children should be encouraged to meet their magnesium requirements by eating a healthy diet high in green vegetables and whole grains and low in fat.

See also Adolescent nutrition ; Cancer-fighting foods ; DASH diet ; Dietary supplements ; Electrolytes ; Fad diets ; Flaxseed ; Gastroesophageal reflux disease (GERD) ; Osteoporosis diet ; Prebiotics and probiotics .