Initial Posting: 6/2/17 Last Update: 10/14/17
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Summary: What You Need to Know About Magnesium Supplements
What It Is:
- Magnesium is an essential mineral for proper metabolism and nervous system functioning. It can be easily obtained through the diet and only a small percentage of people in the U.S. have a magnesium deficiency requiring supplementation. Conditions that may deplete magnesium include alcohol abuse, diabetes, diseases of the digestive tract, and use of medications such as Nexium and Prilosec. Inadequate intake may modestly elevate blood pressure and increase the risk of osteoporosis and fractures. In addition, supplementing with magnesium may be helpful for conditions such as migraines and menstrual pain and it is an effective laxative and antacid. It may also improve glucose status in people with prediabetes -- particularly if they are low in magnesium. Maintaining adequate magnesium intake also has cardiovascular benefits. (See "What It Does"). In short, if you are not getting at least 300 to 400 mg of magnesium from your diet, consider a supplement which will get you to that level.
- Among the products ConsumerLab.com selected for testing, four failed review because they contained less magnesium than listed, were contaminated with lead, failed pill disintegration testing, or had improper labeling (see What CL Found).
- Among the products which passed testing and were "Approved" for their quality, CL selected a Top Pick which is low in price (just 6 cents per pill), well-absorbed, and in a stable chemical form.
- Magnesium comes in several forms: Magnesium oxide tends to be less expensive than other forms, but may also be less well absorbed and more likely to cause diarrhea. Forms such as citrate and chloride may be better absorbed. Magnesium chloride is also less likely to cause diarrhea and is recommended if you are taking a higher dose, but is best in liquid form rather than as a tablet. See "What to Consider When Buying" for more about the different forms.
- Be sure to check that supplements list the amount of elemental "magnesium" and not the amount of the total compound (i.e. magnesium oxide), as this could cause you to get much less magnesium than you think (See "What to Consider When Buying").
- When used as a treatment, magnesium is often recommended at doses of 250 to 600 mg daily (which is similar to the daily intake requirement in adults of about 400 mg). However, unless treating a deficiency, limit your daily intake of magnesium from supplements and fortified foods to no more than 350 mg (the Upper Tolerable Intake Level), to avoid side-effects. You can easily get the rest of your required magnesium from your diet. (See "What to Consider When Using").
- Magnesium supplements may cause upset stomach, nausea, or diarrhea in some people. Although rare, excessive intake can cause thirst, low blood pressure, drowsiness, muscle weakness and slowed breathing (See "Concerns and Cautions").
Magnesium is an essential mineral for the body. It comes in a variety of chemical forms, including magnesium oxide, magnesium chloride, magnesium gluconate, magnesium citrate, magnesium orotate and many others. (For information about how these forms compare, see ConsumerTips™: What to Consider When Buying).
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).
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. (see ConsumerTips™: What to Consider When Using for more information about daily requirements and how to get magnesium from foods). Low serum magnesium levels can also result in serious adverse events including muscle spasm (tetany), irregular heartbeat (arrhythmias), and convulsions (seizures); however, patients do not always have these symptoms. Early signs of magnesium deficiency include loss of appetite, nausea, vomiting, fatigue, and weakness. Severe magnesium deficiency is rare.
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 certain acid blocking drugs (e.g., proton pump inhibitors).
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. Intravenous magnesium (as opposed to oral magnesium supplementation), is sometimes used in hospitals to treat acute asthma, arrhythmias, overdoses of certain drugs, osmotic coma, diabetic ketoacidosis, pancreatitis, hyperthyroidism, hepatitis, and other conditions.
As mentioned earlier, magnesium deficiency can modestly elevate blood pressure. Not surprisingly, an analysis of clinical studies involving magnesium supplementation found that people receiving about 368 mg of magnesium for about three months had modest overall reductions in systolic blood pressure of 2 mm Hg and diastolic blood pressure of 1.78 mm Hg. The study also found that magnesium might only be effective among people with magnesium deficiency or insufficiency (Zhang, Hypertension 2016).
Interestingly, a study which followed thousands of older men and women in the Netherlands for about 9 years found that those with the lowest blood serum magnesium levels (0.8 mmol/L and below) were 36% more likely to die from coronary heart disease and 54% more likely to experience sudden cardiac death over the course of the study than those with moderate levels (0.81 and 0.88 mmol/L) (Kieboom, J Am Heart Assoc 2016). High levels (above 0.89 mmol/L) were associated with a 6% lower risk of coronary heart disease but a 35% greater risk of sudden cardiac death than moderate levels. (Note: Normal magnesium levels range from 0.7 to 0.91 mmol/L or, using units more common in the U.S., 1.7 to 2.2 mg/dL). A study of middle-aged men in Finland followed for around 25 years also found lower serum magnesium to be associated with greater risk of future heart failure (Kunutsor, Eur J Epidemiol 2016).
Magnesium supplements may increase insulin sensitivity in people with type 2 diabetes, many of whom have hypomagnesemia (low blood levels of magnesium). 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 study of people with hypomagnesemia and prediabetes in Mexico found that after 4 months of taking 382 mg of magnesium daily (as a magnesium chloride liquid supplement), 50.8% had improved glucose status versus 7% of those receiving placebo. On average, those taking magnesium had a 22% improvement in fasting glucose levels. During the study, both groups were advised to follow a balanced diet and to engage in physical activity for at least 30 minutes three times a week (Guerrero-Romero, Diab & Metab 2015). A study among obese, insulin insensitive people with normal magnesium plasma levels, showed that 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. Similarly, an analysis of 40 observational studies ranging from 4 to 30 years in length and involving a total of 1 million participants found that each 100 mg/day increase in dietary magnesium intake (up to about 500 mg total daily intake) is associated with a 7% decrease in the risk of stroke, as well as 22%, 19% and 10% decreases in the risks of heart failure, type 2 diabetes, and all-cause mortality, respectively (Fang, BMC Medicine 2016).
Magnesium supplements, especially those containing magnesium-L-threonate (such as in Dr. Mercola Magnesium L-Threonate in the Results Table below), are sometimes promoted for improving memory or preventing memory loss. However, there appears to be only one small clinical study of magnesium's effects on memory in people and it was funded by the makers a magnesium-L-threonate supplement called Magtein (now also sold as Clarimem from Neurocentria, Inc.). The study found that men and women with self-reported memory and concentration impairment, anxiety, and difficulty sleeping who received between 1.5 and 2 grams of magnesium-L-threonate daily for three months had an average 10% increase in the speed of performance on an executive function task, while those who took a placebo showed much smaller improvement. There was no improvement, however, in working memory, episodic memory, attention, anxiety or sleep, relative to placebo. No serious adverse events were reported and there were no significant changes in blood pressure or heart rate (Liu, J Alzheimer's Dis 2015).
A study that tracked over 9,500 adults in the Netherlands for about eight years found that those who began the study with the lowest or highest blood levels of magnesium (respectively, 0.79 mmol/L or less and 0.9 mmol/L or greater) were approximately 30% more likely to develop dementia (predominately Alzheimer's disease) over the course of the study compared to those with mid-range levels (0.84 to 0.85 mmol/L) after adjusting for factors such as age and other diseases. (Kieboom, Neurology 2017). Although this type of study does not prove cause-and-effect, getting the daily requirement of magnesium from one's diet and avoiding excessive magnesium would seem prudent.
Another study found the intake of magnesium laxatives to be associated with reduced risk of dementia, although as with the study above, this does not prove cause-and-effect. The study, among over 6,000 men and women in Taiwan age 50 and older, found that those who were prescribed oral magnesium oxide for the treatment of constipation (average length of usage about 5 months) at the beginning of the study were 48% less likely to develop dementia over a 10 year follow-up period than those who had not taken magnesium oxide, even after adjusting for factors such as age, gender, and other medical conditions (Tzeng, Curr Med Res Opin 2017). Those who took magnesium oxide for more than one year had an even lower risk — they were 59% less likely to develop dementia. Unfortunately, the study did not report the average daily dose of magnesium taken by participants, or take into account the amount of magnesium they were getting from their diet.
Other research of magnesium's effects on memory and cognition has been limited to studies in animals (Slutsky, Neuron 2004; Hoane, Magnes Res 2008; Abumaria, J Neurosci 2011), including one funded by the makers of Magtein that found that rats given magnesium-L-threonate performed significantly better on tests of long and short term memory (Slutsky, Neuron 2010). Magnesium-L-threonate also enhanced signaling of a specific part of brain receptors associated the ability to store information. Other forms of magnesium tested, including magnesium chloride, magnesium citrate, magnesium glycinate, and magnesium gluconate, were not as efficient at raising magnesium levels in the central nervous system (as measured by levels in cerebrospinal fluid) and did not improve memory as well as magnesium-L-threonate.
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 meeting the recommended amount of 420 mg daily were 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.
Higher intake of magnesium (from a combination of food and, if used, supplements) was shown to reduce the risk of bone fracture among older men and women (average age 61) in a study in the U.S. Participants recorded their magnesium intakes and their outcomes were followed for 8 years. Those who reported the highest intakes of magnesium (averaging 491 mg/day for men and 454 mg/day for women) also reported the fewest fractures over the follow-up period. The risk of fracture was 53% and 62% lower, respectively, among men and women with the highest intakes compared to those with the lowest intakes (205 mg/day for men and 190 mg/day for women). It was found that women meeting the RDA for magnesium (350 mg) had a 27% lower risk of fracture than those not meeting the RDA, although no such association was found for men (RDA of 420 mg). Interestingly, only one quarter of participants met the RDA (Veronese, Br J Nutr 2017).
A study in healthy women older than 65 involved in a mild, weekly exercise program found that physical performance improved for those who were given a daily magnesium supplement (300 mg from magnesium oxide) for 12 weeks, compared to those given placebo (Veronese, AJCN 2014). Improvements were seen with activities such as the speed of walking and rising from a chair. Although all the women had normal blood levels of magnesium, improvements in physical performance were more evident in participants with magnesium dietary intake lower than the RDA (320 mg for women 31 years and older), which is common among older women, suggesting that some women may still be "deficient" despite normal blood levels.
Magnesium supplements are sometimes promoted to help relieve symptoms of restless leg syndrome (RLS) but this effect is not well established. One study in 10 men and women with insomnia related to RLS found a dose of 301.38 mg of magnesium (as magnesium oxide) taken in the evening for 4-6 weeks significantly reduced leg movement associated with waking, however, this study was not blinded or placebo-controlled (Hornyak, Sleep 1998).
Similarly, there is little evidence that magnesium supplementation reduces leg cramps or nighttime leg cramps in most people, although there may be a small benefit in pregnant women who experience leg cramps (Garrison, Cochrane Database Syst Rev 2012; Sebo, Fam Pract 2014). Most recently, a study among 88 older men and women (average age 64) in Israel who regularly experienced nighttime leg cramps found that 520 mg of magnesium (as magnesium oxide) taken at bedtime for one month did not decrease frequency, severity or duration of the cramps compared to placebo (Maor, JAMA Intern Med 2017).
Among pregnant women with leg cramps, a study using 300 mg of magnesium (as magnesium bisglycinate chelate) daily showed significant reductions in the intensity and frequency of leg cramps compared to placebo (Supakatisant, Matern Child Nutr 2012), while a study using 360 mg of magnesium (from a combination of magnesium lactate and magnesium citrate) showed no effect on leg cramps (Nygaard, Eur J Obstet Gynecol Reprod Biol 2008).
Magnesium is one of several minerals (including calcium, iron, zinc, sodium, and copper) that make up nails. Some research suggests that people with "soft, flaky nails that are inclined to break or split" may have significantly reduced levels of magnesium in the blood and nail plate (Cashman, Clin Dermatol 2010). However, there do not appear to be any clinical studies on the effects of magnesium supplementation on nail health or strength.
Magnesium supplements do not appear to help prevent kidney stones.
For more information about the clinical findings with magnesium, see the Magnesium article in our Encyclopedia.
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).
Magnesium Creams and Sprays
There is some evidence that magnesium may be absorbed through the skin when magnesium creams or sprays are applied, however, these approaches have generally not been shown to be effective and may cause irritation. In one study, applying a cream containing magnesium (form not known) and MSM (MagPro) on the leg before stretching and exercise had no effect on flexibility or endurance compared to a placebo cream (Gulick, J Strength Cond Res 2012). A pilot study (no placebo control) sponsored at the Mayo Clinic investigated the use of a magnesium chloride spray (Fibro Flex, Magnesium Direct, Inc. — 31% MgCl2) on the quality of life in women with fibromyalgia. Participants were asked to apply (and rub in) 4 sprays per limb 2 times daily for 4 weeks, showering it off before bedtime to avoid transfer to bed sheets. Forty percent of participants dropped out of the study, with 22.5% being due to skin irritation. Overall, the women reported modest improvements cramps and fatigue but no statistically significant improvement in quality of life (Engen, J Integr Med 2015). A small, placebo-controlled study in the UK also found no statistically significant increase in blood levels of magnesium from applying a cream containing a low dose of magnesium chloride (56 mg) to the stomach and legs daily for two weeks (Kass, PLoS One 2017).
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 (including combinations with vitamins D, K, and/or calcium) sold in the U.S. and Canada and tested them to determine whether they possessed the claimed amount of these ingredients. Products sold as regular tablets were tested to determine whether they could disintegrate properly. Products claiming to provide 250 mg or more of minerals or listing whole herbs as ingredients were tested to determine whether they were free of unacceptable levels of lead, cadmium, and arsenic (see Testing Methods and Passing Score).
- Labeled Amount — Does the product really contain the labeled amount of magnesium and other key ingredients such as vitamins D and K and calcium? 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 toxic heavy metals such as lead, cadmium or arsenic. In 2005 and 2009, for example, ConsumerLab.com found magnesium supplements contaminated with lead, and, in 2012, found a combination product containing magnesium, calcium, vitamin D and vitamin K to exceed limits for lead contamination.
- 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.
(7/11/17): A company selling one of the products covered in this Review was recently sent a Warning Letter from FDA indicating that the product is being marketed online with claims regarding its ability to cure, prevent, or treat diseases, and this is not permitted for a supplement. For details, see the "Update" at the top of the full Review.