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Magnesium Supplements Review (Including Calcium, Vitamins D & K, and Boron)
Summary: What You Need to Know About Magnesium Supplements
What is magnesium? Magnesium is an essential mineral for proper metabolism and nervous system functioning, including helping to maintain the electrical stability of the heart. Although magnesium can be easily obtained through the diet and overt magnesium deficiency is not common, many people do not get adequate amounts of magnesium and can benefit from increasing magnesium intake from foods or supplementation. Conditions that may deplete magnesium include alcohol abuse, diabetes, diseases of the digestive tract, and use of medications such as Nexium and Prilosec.
What does magnesium do? Inadequate intake of magnesium 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. It also helps control levels of vitamin D and can boost low levels. Maintaining adequate magnesium intake also has cardiovascular benefits, and maintaining a proper ratio of magnesium to calcium intake may have cognitive benefits (See "What It Does").
How much magnesium do I need?If you are not getting at least 300 to 400 mg of magnesium from your diet, consider a supplement that will get you to that level.
What did CL find? Among the products ConsumerLab.com selected for testing, two magnesium-only supplements failed review because they contained less magnesium than listed or were contaminated with lead and two magnesium formulas failed for incorrect amounts of vitamin D, vitamin K, and/or boron (See What CL Found).
Which magnesium is best? Among the products that passed testing and were "Approved" for their quality, CL selected a Top Pick for magnesium that is low in price (just 6 cents per pill), well-absorbed, and in a stable chemical form. CL also selected Top Picks for combination formulas that include magnesium, such as those marketed for bone health that contain calcium, vitamin D, vitamin K, and/or boron.
How do forms differ? 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. Labels are required to show the amount of elemental magnesium in each serving, but you need to read labels carefully. See "What to Consider When Buying" for more about the different forms.
What's the right dose of magnesium? 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").
What are the side effects of magnesium? 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. Be aware that magnesium can interact with certain supplements and drugs. (See "Concerns and Cautions").
Magnesium Supplements: What You Need to Know -- Dr. Tod Cooperman
What It Is:
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).
What It Does: Magnesium deficiency and insufficiency:
Magnesium is needed for proper metabolism and nervous system functioning, including helping to maintain the electrical stability of the heart. While sufficient magnesium can be obtained easily from the diet, and few people have overt magnesium deficiency, many people get insufficient amounts, particularly men aged 71 and older and adolescent females (Moshfegh, NHANES 2005-2006) (see ConsumerTips™: What to Consider When Using for more information about daily requirements and how to get magnesium from foods).
Magnesium deficiency may modestly elevate blood pressure and increase the risk of osteoporosis. 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).
Several studies have shown a correlation between adequate magnesium levels or magnesium intake and heart health. A study that 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). Similarly, a study in the U.S. that followed over 150,000 postmenopausal women (ages 50 to 79) for an average of ten years found that those with the lowest intakes of dietary magnesium (about 189 mg per day) had a 19% higher risk of fatal coronary heart disease that those with the highest intakes (about 330 mg per day) (Li, J Womens Health (Larchmt) 2019).
Low tissue levels of magnesium may be a contributing risk factor for the development of "torsades de pointes," an abnormal heart rhythm that can cause sudden death. Low blood levels of magnesium have been associated with another type of abnormal heart rhythm known as premature ventricular complexes (PVCs), which are sometimes also referred to as "palpitations." In adults with low blood levels of magnesium (< 0.70 mmol/L), the prevalence of PVCs was found to be twice that of adults with sufficient blood levels of magnesium, according to a study in Canada among obese men and women with type 2 diabetes (Gobbo, Cardiovasc Diabetol 2012). However, a review of the evidence for treating abnormal heart rhythms with magnesium concluded that more research is still needed to determine if correcting magnesium levels improves clinical outcomes (Baker, Eur Heart J Cardiovasc Pharmacother 2017).
Early signs of magnesium deficiency include loss of appetite, nausea, vomiting, fatigue, and weakness. 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. 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.
Dementia and cognition: Adequate intake of magnesium may optimize cognitive function and reduce the risk of developing dementia, as suggested by several studies, although getting too much is not beneficial.
Increasing magnesium intake for 12 weeks in a placebo-controlled study involving 240 healthy individuals in Tennessee was found to improve cognitive function by 9.1% among those aged 65 and older who otherwise consumed high amounts of calcium relative to magnesium. For example, if a person was consuming a total of 1,200 mg of calcium and 300 mg of magnesium per day (a ratio of 4 to 1), that person was assigned a dose of magnesium (as magnesium glycinate — as found in the KAL product in this Review) of 221.7 mg, getting them to a calcium:magnesium ratio of 2.3 to 1. The daily dose ranged from 77.25 mg to 389.55 mg, with the average being 216.5 mg. The magnesium supplementation was found to affect activity at a gene (APOE) that plays a role in calcium signaling in nerve cells and is associated with late-onset Alzheimer's disease. The effects on this gene were associated with the improvements in cognitive function. Magnesium did not have effects on people younger than 65 years of age (Zhu, J Alz Dis 2020). ConsumerLab Note: These findings suggest that supplementing with magnesium to lower high calcium:magnesium ratios may be helpful, but be aware that excessive magnesium intake can have negative effects on cognition and mortality (Dai, BMJ Open 2013) -- do not reduce calcium:magnesium ratios to below 1.7.
A study in the U.S. that followed 6,473 women beginning around 70 years of age for an average of 20 years found that those who consumed between 257 mg and 317 mg of magnesium per day from foods and supplements had a 37% lower risk of developing mild cognitive impairment compared to those who consumed less than 197 mg per day (Lo, BMJ Open 2019).
Somewhat similarly, 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 these types of studies do not prove cause-and-effect, getting the daily requirement of magnesium from one's diet and, if necessary, supplements, and avoiding excessive magnesium would seem prudent.
Another study found the intake of magnesium laxatives to be associated with reduced risk of dementia. 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.
A small study funded by the makers of a magnesium-L-threonate supplement called Magtein (now also sold as Clarimem from Neurocentria, Inc.) 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 2016). Another study that sought to determine if magnesium-L-threonate (600 mg in the morning and 1,200 mg 2 hours before bed time) improved learning and memory in people with dementia was conducted at Stanford University and was completed in mid-2016 but results were not published (ClinicalTrials.gov, accessed 11/21/19).
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. 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 (Slutsky, Neuron 2010).
Magnesium for other conditions: 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 subsequent study by the same researchers involved giving the same dose and form of magnesium to people with low magnesium levels (below 1.8 mg/dL) and metabolic syndrome, which is a combination of high blood pressure and blood sugar, excess body fat around the waist, and low HDL-c. After four months, only 48% of those given magnesium had metabolic syndrome compared to 77.5% of those given placebo. The treated group experienced significantly greater improvements in blood pressure, fasting glucose, and triglycerides (Rodriguez-Moran, Adv Chronic Kidney Dis 2018). 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).
Some observational studies have found that low blood levels of magnesium and low magnesium intake from food are each associated with an increased risk of depression (Islam, BMC Psychiatry 2018; Cheungpasitporn, Intern Med J 2015; Yary, Biol Trace Elem Res 2013). Supplementing depressed individuals with magnesium has shown some promise in preliminary studies, although none of the studies were placebo-controlled making it impossible to determine true efficacy. These studies, which lasted from 6 weeks to 3 months, involved daily doses of 250 mg to 300 mg of magnesium (from magnesium citrate or chloride) (Barragán-Rodrí, Magnes Res 2008; Bagis, Rheumatol Int 2013) to as much as 450 mg (from magnesium chloride liquid) in a study involving people with low blood levels of magnesium (Tarleton, PLoS One 2017). The studies showed comparable results to tricyclic antidepressants or improvements over no treatment (meaning the subjects were aware of when they were given the treatment or not). A study in Iran among 60 young men and women (average age 20) with moderate depression and magnesium blood levels at the lower end of normal found that 250 mg of magnesium (from magnesium oxide) taken twice daily for two months modestly reduced symptoms of depression compared to placebo (an average reduction of 16 points vs. 10 points on a scale of 0 - 63). In those who took magnesium, blood levels increased from an average of 1.77 mg/dL to 2.08 mg/dL, while there was no change in magnesium levels in those who took the placebo (Rajizadeh, Nutrition 2017). If you have depression, it would seem prudent to at least make sure you are getting adequate magnesium from your diet and/or supplements.
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 or 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). This association between higher magnesium intake and better bone health, however, was not seen in an analysis of older people in Taiwan that focused exclusively on use of magnesium oxide (typically taken as a laxative or antacid). It found that people who used magnesium oxide supplements were 66% more likely over a 5-year period to suffer a hip fracture than people who had not used magnesium oxide (Wu, Osteopor Int 2020).
Getting adequate magnesium has been shown to help maintain optimal blood levels of the active form of vitamin D, boosting lower levels and, in some cases, moderating high levels (See Vitamin D Review).
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.
A small study among healthy male recreational endurance runners (average age 27) who consumed a diet low in magnesium (< 260 mg per day) found that supplementing with magnesium (166.6 mg taken 3 times a day [500 mg total] from magnesium oxide) for 7 days prior to a timed 10 kilometer downhill treadmill run reduced muscle soreness by 32% in the first 24 hours after the run and by 53% three days after the run in comparison to placebo. In addition, blood levels of a marker of inflammation (IL-6) were lower 24 hours after running when magnesium had been taken versus placebo. However, supplementation did not improve running performance, decrease muscle damage, or increase recovery of muscle strength. It should be noted that 500 mg of magnesium is above the daily upper tolerable intake level for magnesium and can cause a laxative effect. The published study failed to report on side effects (Steward, Eur J Appl Physiol 2019).
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 (Garrison, Cochrane Database Syst Rev 2012; Sebo, Fam Pract 2014). For example, 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).
The evidence is mixed regarding the benefit of magnesium supplementation for pregnant women who experience leg cramps. 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). A study in Brazil among 132 women in the first trimester of pregnancy found that 300 mg of magnesium (as magnesium citrate) taken once daily for one month did not decrease the occurrence or frequency of leg cramps compared to placebo (Araujo, PLoS One 2020).
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.
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.
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, Sprays and Oils
There is some evidence that magnesium may be absorbed through the skin, but the amount absorbed may be minimal and topical magnesium products have not been shown to be effective for any condition. Furthermore, they may cause irritation. In one study, applying a cream containing magnesium (form not identified) 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). In a pilot study of a magnesium chloride spray (Fibro Flex, Magnesium Direct, Inc. — 31% MgCl2) on the quality of life in women with fibromyalgia, women reported modest improvements cramps and fatigue but there was no placebo control and no statistically significant improvement in quality of life. 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 (Engen, J Integr Med 2015). A small, placebo-controlled study in the UK 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).
Magnesium "oil," which is technically not an oil but a solution of magnesium (typically magnesium chloride) and water, is also promoted to increase magnesium levels in the body and have other beneficial effects. A study among nine men and women found that daily use of a magnesium oil spray containing 31% magnesium chloride (BetterYou Magnesium Oil Original spray — 20 sprays per day anywhere on the body), plus a twice weekly magnesium foot soak (BetterYou Magnesium Oil Original Soak —100 mL, 31% magnesium chloride) for three months increased cellular magnesium levels (as measured by hair samples) by an average of 59.7%. However, there was no placebo control, the significance of magnesium in hair samples has not been established, and blood/serum levels of magnesium were not measured (Watkins, Eur J Nutr Res 2010). In a study conducted by Dr. Norman Shealy (Shealy Wellness Clinic, Fair Grove, Missouri) in which participants performed a 20-minute foot-soak with transdermal magnesium chloride bath flakes and sprayed their entire body with magnesium oil once daily for one month, intercellular levels of magnesium (as measured in skin cells swabbed from the mouth) were reported to increase from 31.4 mEq/L to 41.2 mEq/L. However, this study does not appear to have been placebo-controlled or published in a peer-reviewed journal.
Be aware that some companies selling topical magnesium products claim that the skin irritation caused by these products is an indication of low magnesium levels in the body. There does not appear to be evidence supporting this claim.
Epsom salt baths
Although no peer-reviewed studies have been published on the absorption of magnesium from Epsom salt (magnesium sulfate) baths, a non-controlled and undated study performed at the University of Birmingham (published by the Epsom Salt Council) showed that soaking in a bath with Epsom salts (flakes or granules of magnesium sulfate) increased concentrations of magnesium in the blood and urine. In the study, 19 men and women (ages 19 to 64) soaked for 12 minutes in a hot bath (122° to 131° F) in a standard bathtub with 400 mg to 600 grams (0.9 to 1.3 lb) of Epsom salt added to 15 gallons of bath water (2 cups of Epsom salt is about 1lb). This was repeated daily for seven days. After the first bath, levels of magnesium in the blood rose by an average of 9% and, after seven days, by 35% (excluding two people with no significant increase), and magnesium levels in the urine rose on average by 109% -- indicating that magnesium was being absorbed as well as excreted. Sulfate levels in the blood and urine also increased.
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:
Labeled Amount — Does the product really contain the labeled amount of magnesium and other key ingredients such as vitamins D and K and calcium and boron? 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.
ConsumerLab.com, as part of its mission to independently evaluate products that affect health, wellness, and nutrition, purchased many leading magnesium-containing supplements 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).