Initial Posting: 5/25/12 Updated: 5/25/13
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What It Is:
Magnesium is an essential mineral for the body. It has been estimated that 15% of adults in the U.S. take a supplement containing magnesium (see ConsumerTips™: What to Consider When Using for more information about daily requirements and magnesium in foods). In addition to magnesium-only supplements, supplemental magnesium can be obtained from laxatives, antacids, multivitamin/multimineral products (see Multivitamin/Multimineral Product Review) and calcium supplements containing magnesium (some of which are included in this Review as well in as the Calcium Product Review).
Magnesium comes in a variety of chemical forms, including magnesium oxide, magnesium chloride, magnesium gluconate, magnesium citrate, magnesium orotate and many others. (See ConsumerTips™: What to Consider When Buying for more information about forms of magnesium).
What It Does:
Magnesium is needed for proper metabolism and nervous system functioning. While sufficient magnesium can be obtained easily from the diet, magnesium deficiency may affect a small percentage of the population, in whom it may modestly elevate blood pressure and increase the risk of osteoporosis. Conditions that may deplete magnesium include alcohol abuse, diabetes, diseases of the digestive tract (such as ulcerative colitis, Crohn's disease and celiac sprue), and use of medications such as cisplatin, certain diuretics, and certainacid blocking drugs (e.g., proton pump inhibitors). Low serum magnesium levels can result in serious adverse events including muscle spasm (tetany), irregular heartbeat (arrhythmias), and convulsions (seizures); however, patients do not always have these symptoms. Severe magnesium deficiency is rare.
The FDA in 2011 warned that proton pump inhibitor (PPI) medications (used to reduce stomach acid) may also cause low serum magnesium levels if taken for prolonged periods of time (in most cases, longer than one year). Examples of PPIs are Nexium, Dexilant, Prilosec, Prevacid, Protonix, AcipHex, Vimovo, and Zegerid. Treatment of hypomagnesemia generally requires magnesium supplements. However, in approximately one-quarter of the cases reviewed, magnesium supplementation alone did not improve low serum magnesium levels and the PPI had to be discontinued.
Magnesium for other conditions:
Use of magnesium supplements may help prevent a number of conditions including: hearing loss from excessive noise, migraine headaches (including menstrual migraines), menstrual pain and PMS. Magnesium is also an effective laxative and antacid.
The evidence is mixed as to whether magnesium supplements increase insulin sensitivity in people with type 2 diabetes, many of whom have hypomagnesemia (low blood levels of magnesium). However, increased intake of magnesium from the diet and supplements has generally been associated with a decrease in the risk of developing type 2 diabetes — particularly among people with magnesium intakes below the Recommended Daily Allowance (RDA) (Larsson, J Intern Med 2007). A recent study showed that even among obese, insulin insensitive people with normal magnesium plasma levels, daily magnesium supplementation improved insulin sensitivity. A 7% improvement in fasting plasma glucose levels was observed among those taking 365 mg of magnesium (as magnesium-aspartate-hydrochloride) daily for 6 months -- a significant improvement compared those taking placebo (Mooren, Diab Obes Metab 2010).
An analysis of several studies concluded that magnesium may help reduce the risk of stroke. People who consumed 100 mg of magnesium more per day than average (the average being about 300 mg) had an 8% lower risk of strokes of any kind and a 9% lower risk of ischemic stroke (Larsson, Am J Clin Nutr 2012). This finding is based on total magnesium in the diet -- it does not mean that 100 mg of magnesium from a supplement will necessarily have the same risk-lowering effect, but getting a total of at least 400 mg of magnesium from your diet per day may be beneficial.
Despite some claims to the opposite, there is some evidence suggesting that oral magnesium supplements do NOT help prevent the heart irregularity called atrial fibrillation, nor help prevent kidney stones. It may, however, reduce anginal attacks in people with coronary artery disease. Intravenous magnesium, rather than oral magnesium supplements, is sometimes used in hospitals to treat acute asthma, overdoses of certain drugs, osmotic coma, diabetic ketoacidosis, pancreatitis, hyperthyroidism, hepatitis, and other conditions.
In a study of elderly men and women aged 70-79 years, magnesium intake from food and supplements was associated with a significant increase in bone mineral density (BMD) in white men and women, but not in black men and women. Most people in this study did not have adequate magnesium intake. In white women, getting the recommended amount of 320 mg daily of magnesium was associated with a 2% higher BMD compared to intakes 220 mg or lower. Similarly, in men, intake levels meeting the recommended amount of 420 mg daily was associated with a 1% higher BMD compared intakes of 320 mg or lower (Ryder, J Am Geriatr Soc 2005). This does not, however, indicate that getting more than the daily requirement is beneficial, nor that a supplement is necessary if you get sufficient magnesium in your diet. Similarly, a recent study in children aged 4-8 years showed that dietary intake of magnesium was associated with significant increases in bone mineral content, but, for most children, daily intake was adequate to meet growth-related needs (Abrams, Pediatric Academic Societies 2013).
Magnesium orotate is a complex of magnesium plus orotic acid. Although it has been promoted to improve athletic performance, there is no reliable evidence to support this. However, a preliminary clinical study in people with heart failure found that giving 6,000 mg of magnesium orotate daily for one month, followed by 3,000 mg daily for 11 months reduced the risk of dying during the study by about 25%. It also improved heart failure symptoms in about 40% of patients (Stepura, Int J Cardiol 2009). However, there are potential safety concerns with magnesium orotate (see Concerns and Cautions).
For more information about the clinical uses of magnesium see the excellent article in the Encyclopedia on this website.
Quality Concerns and What CL Tested for:
Like other supplements, neither the FDA nor any other federal or state agency routinely tests magnesium products for quality prior to sale. However, quality issues for magnesium supplements can include the following:
ConsumerLab.com, as part of its mission to independently evaluate products that affect health, wellness, and nutrition, purchased many leading magnesium supplements products sold in the U.S. and tested them to determine whether they 1) possessed the claimed amount of magnesium, 2) could disintegrate properly in order to be available for absorption, and 3) were free of unacceptable levels of lead (see Testing Methods and Passing Score).
- Labeled Amount — Does the product really contain the labeled amount of magnesium? Too little magnesium in a supplement is a problem if relying on it to prevent or correct a deficiency. Excessive consumption of oral magnesium frequently causes diarrhea. While it is unlikely that an individual with healthy kidneys can take enough magnesium orally to elevate blood levels, if this does occur, potentially dangerous heart and nerve-related symptoms may develop. (Individuals with severe kidney disease should not take magnesium supplements.)
- Purity — Many sources of magnesium, like other minerals, may naturally contain amounts of heavy metals such as lead. In 2005 and 2009, for example, ConsumerLab.com found magnesium supplements contaminated with lead. In children, infants, and fetuses, even low levels of lead can adversely affect neurobehavioral development and cognitive function. In adults, lead at somewhat higher levels can cause elevated blood pressure, anemia, and adversely affect the nervous and reproductive systems. Lead is of particular concern during pregnancy as the mother can transfer it to the fetus.
- Ability to Break Apart for Absorption — Will pills break apart properly so they can release their ingredients in the body? For a tablet to be most useful, it must fully disintegrate prior to leaving the stomach, delivering its contents for absorption in the gut. Some tablets and caplets are not properly made and can pass through your body completely or partially intact, depriving you of its ingredients. Remnants of such products are sometimes found in the stool. This happens, for example, when a tablet is too tightly compressed (too "hard") or is too thickly coated.
- Side Effects at Suggested Dosage — ConsumerLab.com reviewed the levels of magnesium to determine if any product provided doses high enough so as to carry a risk of adverse side effects. Those that exceeded upper tolerable limits (ULs — see discussion below) are footnoted.