Synonym: magnesium
Characteristics: Magnesium, an abundant mineral in the body, is naturally present in many foods, is available as a dietary supplement or in the form of medicines (such as antacids and laxatives). It is needed for overall physical health as it supports cell functions throughout the body. Magnesium is a cofactor in more than 300 enzyme systems that regulate various biochemical reactions in the body (e.g. protein synthesis), muscle and nerve functions, control blood glucose and regulate blood pressure. As a cofactor of numerous enzymatic reactions, magnesium fulfills various intracellular physiological functions. Thus, an imbalance of magnesium status, primarily hypomagnesemia, which is observed more often than hypermagnesemia, can lead to undesirable neuromuscular, cardiac, or nervous disorders. Magnesium also plays a role in the active transport of calcium and potassium ions across cell membranes, a process that is important for the conduction of nerve impulses, muscle contraction and normal heart rhythm. Finally, magnesium is essential for energy production, for the synthesis of DNA, RNA, and the antioxidant glutathione. The body of an adult human contains approximately 25 g of magnesium, with 50‒60% present in bones and the rest in soft tissues.
Absorption: Approximately 30‒40% of magnesium taken in food is absorbed. The absorption of magnesium from different types of dietary supplements varies. Approximately 24–76% of ingested magnesium is absorbed in the gastrointestinal tract, primarily by passive paracellular absorption in the small intestine.
Dietary supplements: Forms of magnesium that dissolve well in liquid are better absorbed in the gut than less soluble forms. Thus, magnesium in the form of aspartate, citrate, lactate, and chloride is absorbed more completely and is more biologically available than magnesium oxide and magnesium sulfate. Very high doses of zinc from dietary supplements (142 mg/day) can interfere with the absorption of magnesium and thus disturb the balance of magnesium in the body.
Natural sources: Good sources of magnesium are green leafy vegetables due to their chlorophyll content (spinach), legumes, nuts, seeds, and whole grains. In general, foods containing fiber provide magnesium. Dark chocolate is also an excellent source. Magnesium is also added to some breakfast cereals and other fortified foods. Unfortunately, some types of food processing, such as refining grains in ways that remove the nutrient-rich germ and bran, substantially reduce magnesium content. A source of magnesium can also be tap, mineral and bottled water, in which the amount of magnesium varies by source and brand (ranging from 1 mg/L to more than 120 mg/L).
Effect: Magnesium is a component of some laxatives and medicines to treat heartburn and indigestion. Low magnesium intake causes changes in biochemical pathways that can increase the risk of various diseases over time. Magnesium is recommended in the treatment of hypertension and cardiovascular diseases, type 2 diabetes, osteoporosis, and migraines. Magnesium sulfate is indicated for the therapy of preeclampsia.
Deficiency: Symptomatic magnesium deficiency due to low dietary intake is not common in otherwise healthy people because the kidneys limit urinary excretion of this mineral. However, low intake or excessive losses of magnesium due to certain medical conditions, chronic alcoholism, and/or the use of certain medications can lead to magnesium deficiency. Early symptoms of magnesium deficiency include loss of appetite, nausea, vomiting, fatigue, and weakness. As magnesium deficiency worsens, numbness, tingling, muscle contractions and spasms, seizures, personality changes, and abnormal heart rhythms may occur. Severe magnesium deficiency can lead to hypocalcemia or hypokalemia (low serum calcium or potassium levels, respectively) because mineral homeostasis is disrupted. Chronic diarrhea and fat malabsorption due to Crohn's disease, celiac disease, and enteritis can cause magnesium deficiency over time. Resection or bypass of the small intestine, especially the ileum, also results in magnesium malabsorption and loss. People with insulin resistance and/or type 2 diabetes may develop magnesium deficiency and increased urinary magnesium excretion. Magnesium deficiency is common in people with chronic alcoholism and older adults, in whom magnesium absorption from the gut decreases with age and magnesium excretion by the kidneys increases. Older adults are also more likely to have chronic diseases or take medications that alter magnesium status, which can increase the risk of magnesium depletion.
Recommended daily dose: adult: 420 mg for men, 320 mg for women (360 mg during pregnancy, 320 mg during breastfeeding).
Adverse Effects: Too much dietary magnesium does not pose a health risk in healthy individuals because the kidneys excrete excessive amounts of urine. However, high doses of magnesium from supplements or drugs often lead to diarrhea, which can be accompanied by nausea and abdominal cramps. The most reported forms of magnesium that cause diarrhea include magnesium carbonate, chloride, gluconate, and magnesium oxide. Diarrhea and laxative effects of magnesium salts are caused by the osmotic activity of unabsorbed salts in the intestine and the stimulation of motility (movement) of the digestive tract.
Interactions: Magnesium-rich dietary supplements or medications may decrease absorption of oral bisphosphonates such as alendronate, which is used to treat osteoporosis (at least 2 hours apart). Magnesium can form insoluble complexes with tetracyclines (doxycycline) as well as with quinolone antibiotics such as ciprofloxacin and levofloxacin. These antibiotics should be taken at least 2 hours before or 4-6 hours after a magnesium-containing product. Chronic treatment with loop diuretics such as furosemide and thiazide diuretics such as hydrochlorothiazide may increase urinary magnesium loss. In contrast, potassium-sparing diuretics such as amiloride and spironolactone reduce magnesium excretion. Proton pump inhibitors (used to treat acid reflux) such as esomeprazole and lansoprazole can cause hypomagnesemia when used long-term (typically longer than a year).
Pregnancy: Safe in usual doses.
Breastfeeding: Safe in usual doses.
Warning: The kidneys are responsible for excreting magnesium from the body. If you suffer from their insufficient function or need dialysis, consult your doctor about the recommended dosage of magnesium, as it can be toxic.
Toxicity: Very high doses of magnesium-containing laxatives and antacids (usually providing more than 5,000 mg magnesium/day) have been toxic. Symptoms of magnesium toxicity may include hypotension, nausea, vomiting, facial flushing, urinary retention, ileus, muscle weakness, difficulty breathing, irregular heartbeat, and cardiac arrest. The risk of magnesium toxicity increases with renal impairment or kidney failure because the ability to remove excess magnesium is reduced or lost.
