What is Magnesium?
Magnesium, an abundant mineral in the body, is naturally present in many foods, added to other food products, available as a dietary supplement, and present in some medicines (such as antacids and laxatives). Magnesium is a cofactor in more than 300 enzyme systems that regulate diverse biochemical reactions in the body, including protein synthesis, muscle and nerve function, blood glucose control, and blood pressure regulation [1-3]. Magnesium is required for energy production, oxidative phosphorylation, and glycolysis. It contributes to the structural development of bone and is required for the synthesis of DNA, RNA, and the antioxidant glutathione. Magnesium also plays a role in the active transport of calcium and potassium ions across cell membranes, a process that is important to nerve impulse conduction, muscle contraction, and normal heart rhythm .
Sources of Magnesium
Magnesium is widely distributed in plant and animal foods and in beverages. Green leafy vegetables, such as spinach, legumes, nuts, seeds, and whole grains, are good sources [1,3]. In general, foods containing dietary fiber provide magnesium. Magnesium is also added to some breakfast cereals and other fortified foods. Some types of food processing, such as refining grains in ways that remove the nutrient-rich germ and bran, lower magnesium content substantially . Selected food sources of magnesium are listed in Table 2.
Tap, mineral, and bottled waters can also be sources of magnesium, but the amount of magnesium in water varies by source and brand (ranging from 1 mg/L to more than 120 mg/L) .
Approximately 30% to 40% of the dietary magnesium consumed is typically absorbed by the body [2,9].
Magnesium supplements are available in a variety of forms, including magnesium oxide, citrate, and chloride [2,3]. The Supplement Facts panel on a dietary supplement label declares the amount of elemental magnesium in the product, not the weight of the entire magnesium-containing compound.
Absorption of magnesium from different kinds of magnesium supplements varies. Forms of magnesium that dissolve well in liquid are more completely absorbed in the gut than less soluble forms [2,11]. Small studies have found that magnesium in the aspartate, citrate, lactate, and chloride forms is absorbed more completely and is more bioavailable than magnesium oxide and magnesium sulfate [11-15]. One study found that very high doses of zinc from supplements (142 mg/day) can interfere with magnesium absorption and disrupt the magnesium balance in the body .
Intake recommendations for magnesium and other nutrients are provided in the Dietary Reference Intakes (DRIs) developed by the Food and Nutrition Board (FNB) at the Institute of Medicine of the National Academies (formerly National Academy of Sciences) . DRI is the general term for a set of reference values used to plan and assess nutrient intakes of healthy people. These values, which vary by age and sex, include:
Recommended Dietary Allowance (RDA): average daily level of intake sufficient to meet the nutrient requirements of nearly all (97%–98%) healthy individuals.
Adequate Intake (AI): established when evidence is insufficient to develop an RDA and is set at a level assumed to ensure nutritional adequacy.
Estimated Average Requirement (EAR): average daily level of intake estimated to meet the requirements of 50% of healthy individuals. It is usually used to assess the adequacy of nutrient intakes in population groups but not individuals.
Tolerable Upper Intake Level (UL): maximum daily intake unlikely to cause adverse health effects.
Table 1 lists the current RDAs for magnesium . For infants from birth to 12 months, the FNB established an AI for magnesium that is equivalent to the mean intake of magnesium in healthy, breastfed infants, with added solid foods for ages 7–12 months.
Magnesium is available in many forms. Recommended forms include magnesium citrate, magnesium gluconate, and magnesium lactate, all of which are more easily absorbed into the body than other forms. Time release preparations may improve absorption.
Other familiar sources are magnesium hydroxide (often used as a laxative or antacid) and magnesium sulfate (generally used orally as a laxative or in multivitamins, or added to a bath). Some magnesium, such as Epsom salts, can be absorbed through the skin. Preliminary research suggests Epsom salts can relieve swelling, inflammation, and ease muscle aches and pains.
Benefits of Magnesium Supplements
“Several studies show that intravenous (IV) magnesium and magnesium inhaled through a nebulizer can help treat acute attacks of asthma in adults and children, 6 to 18 years of age.”
“Inadequate magnesium appears to reduce serotonin levels, and antidepressants have been shown to raise brain magnesium. One study found that magnesium was as effective as tricyclic antidepressants in treating depression among people with diabetes.”
“People who have type 2 diabetes often have low blood levels of magnesium. A large clinical study of more than 2,000 people found that getting more magnesium in the diet may help protect against type 2 diabetes. Some studies suggest that taking magnesium supplements may help blood sugar control and insulin sensitivity in people with diabetes or prediabetes.”
“A preliminary clinical study of 24 people with fibromyalgia found that a proprietary tablet containing both malic acid and magnesium improved pain and tenderness associated with fibromyalgia when taken for at least 2 months.”
“One study suggests that taking magnesium may prevent temporary or permanent hearing loss due to very loud noise.”
“Too much magnesium from food does not pose a health risk in healthy individuals because the kidneys eliminate excess amounts in the urine. However, high doses of magnesium from dietary supplements or medications often result in diarrhea that can be accompanied by nausea and abdominal cramping.”
“Very large doses of magnesium-containing laxatives and antacids (typically providing more than 5,000 mg/day magnesium) have been associated with magnesium toxicity, including fatal hypermagnesemia in a 28-month-old boy and an elderly man . Symptoms of magnesium toxicity, which usually develop after serum concentrations exceed 1.74–2.61 mmol/L, can include hypotension, nausea, vomiting, facial flushing, retention of urine, ileus, depression, and lethargy before progressing to muscle weakness, difficulty breathing, extreme hypotension, irregular heartbeat, and cardiac arrest.”
Magnesium is a chemical element with symbol Mg and atomic number 12. It is a shiny gray solid which bears a close physical resemblance to the other five elements in the second column (Group 2, or alkaline earth metals) of the periodic table: all Group 2 elements have the same electron configuration in the outer electron shell and a similar crystal structure.
Magnesium is the eleventh most abundant element by mass in the human body and is essential to all cells and some 300 enzymes. Magnesium ions interact with polyphosphate compounds such as ATP, DNA, and RNA. Hundreds of enzymes require magnesium ions to function. Magnesium compounds are used medicinally as common laxatives, antacids (e.g., milk of magnesia), and to stabilize abnormal nerve excitation or blood vessel spasm in such conditions as eclampsia.