Magnesium

Magnesium is an essential mineral and the fourth most abundant cation in the human body. An adult body contains approximately 25 grams of magnesium, with about 50–60% stored in bone and most of the remainder in soft tissue.¹ Magnesium serves as a cofactor in more than 300 enzyme systems that regulate diverse biochemical reactions including protein synthesis, muscle and nerve function, blood glucose control, and blood pressure regulation. It is also required for energy production, oxidative phosphorylation, and glycolysis, and it contributes to the structural development of bone.¹

Several forms of magnesium are used in dietary supplements, and they differ in elemental magnesium content and bioavailability:¹

• Magnesium oxide: high elemental magnesium content per gram but lower bioavailability
• Magnesium citrate: moderate bioavailability; often used for gastrointestinal effects
• Magnesium glycinate (bisglycinate): generally well-tolerated and a common choice when minimizing gastrointestinal side effects is a priority
• Magnesium chloride and magnesium lactate: generally well-absorbed
• Magnesium L-threonate: a less common form that has been studied for potential cognitive applications

NIH ODS notes that the available evidence comparing the various forms is limited, and that absorption differences may matter less in practice than the total elemental magnesium delivered.¹

Magnesium is required for normal physiological function across many systems, and its dietary inadequacy has been associated with several health outcomes. Magnesium supplementation is used for clinically diagnosed hypomagnesemia, which can result from gastrointestinal losses, renal losses, chronic alcohol use, certain medications (including proton pump inhibitors, diuretics, and some antibiotics), and other conditions.¹

Magnesium has been studied for a range of additional applications including cardiovascular health (with observational and some intervention evidence suggesting an association between higher intake and lower blood pressure or reduced cardiovascular event risk), type 2 diabetes (where lower magnesium status has been associated with higher risk), migraine prevention (where some clinical trials have shown benefit at supplemental doses), and bone health (in conjunction with adequate calcium and vitamin D).¹ Evidence strength varies by application; magnesium's role as an essential nutrient is well-established, while specific therapeutic claims are supported with varying levels of evidence.

Recommended Dietary Allowances for adults (combined from food, beverages, and supplements):¹

• Men 19–30 years: 400 mg/day; 31 years and older: 420 mg/day
• Women 19–30 years: 310 mg/day; 31 years and older: 320 mg/day
• Pregnancy: 350–360 mg/day depending on age
• Lactation: 310–320 mg/day depending on age

The Tolerable Upper Intake Level for supplemental magnesium (from dietary supplements and medications only, not including food) is 350 mg/day for adults.¹ This limit is based on the gastrointestinal effects of high-dose supplemental magnesium, not on intake from food, which is not subject to a UL.

NHANES data indicate that many adults in the United States consume less magnesium from food than the RDA recommends.¹

Real-world practice: Form matters significantly. Magnesium oxide (the most common and cheapest form) has poor absorption and is primarily useful as a laxative. Magnesium glycinate and threonate are generally better tolerated than oxide; users selecting a form for daily use often choose these when minimizing gastrointestinal side effects matters. Magnesium citrate is a middle ground — better absorbed than oxide, less expensive than glycinate. Some users take magnesium in the evening; relaxation effects are reported anecdotally but the magnitude varies by individual.

Oral. Magnesium is also used as an ingredient in over-the-counter laxatives (magnesium hydroxide, magnesium citrate) and in topical preparations, though dermal absorption of magnesium has not been well-characterized in controlled studies.

Standard storage in a cool, dry place. No refrigeration required for oral supplements.

The most common side effect of supplemental magnesium is diarrhea, which results from unabsorbed magnesium drawing water into the bowel; this effect is the basis for magnesium's use as an over-the-counter laxative.¹ Magnesium oxide and magnesium citrate are more likely to produce this effect than magnesium glycinate, which is one reason the glycinate form is often preferred for daily supplementation when gastrointestinal tolerance is a concern.

Magnesium can interact with several medications:¹

• Bisphosphonates: magnesium reduces absorption of oral bisphosphonates; doses should be separated by at least 2 hours
• Antibiotics: magnesium can reduce absorption of tetracyclines and quinolones; timing separation is required
• Diuretics: loop and thiazide diuretics increase urinary magnesium excretion, while potassium-sparing diuretics may decrease it
• Proton pump inhibitors: long-term PPI use has been associated with hypomagnesemia

Individuals with significantly impaired kidney function are at higher risk of magnesium accumulation and toxicity, since the kidney is the primary route of magnesium excretion.¹ Magnesium supplementation should be discussed with a healthcare provider in this setting.