The recommended dietary allowance (RDA) of magnesium for adults is 410–420 mg/day for men and 320–360 mg/day for women. This includes magnesium from all sources such as food, beverages, supplements, and medications. The tolerable upper intake level (UL) for magnesium for adults is 350 mg; this value only includes magnesium obtained from dietary supplements and medications.

Which forms of magnesium are best for people who are looking to increase their magnesium levels for general purposes or to correct a deficiency? Magnesium citrate appears to have the highest bioavailability of all of the forms of magnesium,^[1] followed by magnesium lactate. Magnesium chloride, magnesium gluconate, and magnesium glycinate also appear to have good bioavailability.^[2] On the other hand, magnesium oxide and magnesium carbonate have extremely poor absorption and aren’t recommended for the purpose of increasing magnesium levels in the body.

Magnesium citrate — especially potassium magnesium citrate — and magnesium lactate also appear to carry a lower risk of gastrointestinal side effects and diarrhea compared to other formulations.^[2] Side effects seem to be reported more frequently when supplementing with magnesium carbonate and magnesium oxide, though gastrointestinal issues can occur with any type of magnesium supplement if too high of a dose is taken. Although magnesium sulfate (Epsom salt) is often used in bath preparations to soothe achy and sore muscles, there’s a lack of evidence to support the transdermal (through the skin) absorption of magnesium.^[3] A warm soak might be relaxing, but it’s not due to the magnesium.