Summary
-
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 (see What It Is). -
How do you know if you need to take magnesium?
Although magnesium can be easily obtained through the diet and overt magnesium deficiency is not common, nearly half the U.S. population does not get adequate amounts of magnesium and can benefit from increasing magnesium intake from foods or supplementation. People most likely to get inadequate magnesium are adolescents and those over age 70. 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 of magnesium may modestly elevate blood pressure and increase the risk of osteoporosis and fractures. Early signs of magnesium deficiency include loss of appetite, nausea, vomiting, fatigue, and weakness (see Magnesium Deficiency and Insufficiency). -
What does magnesium do?
In addition to boosting intake, 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). -
What did CL's tests of magnesium find?
Among the magnesium supplements ConsumerLab.com selected for testing, four failed review because they contained less magnesium than listed or inaccurate amounts of other key ingredients (see What CL Found). 
Which magnesium is best?
CL selected a Top Pick for magnesium that is relatively well-absorbed, low in price (just pennies per pill), in a stable chemical form, and unlikely to cause diarrhea at moderate doses. CL also selected Top Picks for supplements combining magnesium with calcium, vitamin D, vitamin K, and/or boron.-
How do forms of magnesium differ?
Magnesium comes in many 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 that are more water soluble, such as magnesium chloride, citrate and many chelate forms (e.g., bisglycinate), may be better absorbed. Magnesium chloride is less likely to cause diarrhea and is recommended if you are taking a higher dose but it is best in liquid form rather than as a tablet, as it tends to attract and hold water, which can cause pills to disintegrate and create problems with supplement storage. Some magnesium chelates are also less likely to cause diarrhea but are bulky, requiring larger pills to get the same amount of elemental magnesium. 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?
Most people can get the daily required magnesium from their diet. 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. Supplementing with about 200 mg should generally be sufficient and safe.
When used to treat known deficiency, magnesium is often recommended at doses of 250 to 600 mg daily. However, unless treating a deficiency, limit your daily intake of magnesium from supplements and fortified foods to no more than 350 mg (the Tolerable Upper 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).
-
How can the recommended Daily Value (DV) for magnesium be higher than the Tolerable Upper Intake Level (UL)?
Side effects are not likely to occur from magnesium naturally in foods. -
Safety and side effects of magnesium:
Magnesium supplements may cause upset stomach, nausea, or diarrhea in some people. If using a powder form of magnesium, be sure to completely dissolve the powder in water before taking to avoid injury to the esophagus. Although rare, excessive intake of magnesium 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).
