Magnesium is an essential mineral involved in hundreds of bodily functions, from energy production to muscle and nerve function. While magnesium is vital for health, it’s important to understand the potential risks of excessive intake. This article explores the question of “How Much Is Too Much Magnesium,” focusing on safe upper limits, potential side effects, and factors that influence magnesium toxicity.
Magnesium is a naturally occurring mineral found in various foods, dietary supplements, and medications like antacids and laxatives. It plays a critical role as a cofactor in over 300 enzyme systems that regulate biochemical reactions in the body. These reactions include protein synthesis, muscle and nerve function, blood glucose control, and blood pressure regulation [1-3]. Magnesium is essential for energy production, oxidative phosphorylation, and glycolysis. It contributes to bone structural development and is required for DNA, RNA, and the antioxidant glutathione synthesis. Furthermore, it facilitates the active transport of calcium and potassium ions across cell membranes, which is vital for nerve impulse conduction, muscle contraction, and maintaining a normal heart rhythm [3].
The adult body contains approximately 25 g of magnesium, with 50%-60% stored in bones and the remainder in soft tissues [4]. Less than 1% is present in blood serum, where levels are tightly regulated between 0.75 and 0.95 millimoles (mmol)/L [1,5]. Hypomagnesemia is defined as a serum magnesium level below 0.75 mmol/L [6]. The kidneys primarily control magnesium homeostasis, typically excreting around 120 mg daily through urine [2], with reduced excretion during low magnesium status [1]. Assessing magnesium levels is challenging, as most of it resides within cells and bones [3]. Serum magnesium concentration is the most common measurement, but it doesn’t accurately reflect total body magnesium levels or tissue concentrations [6]. Other assessment methods include measuring magnesium levels in erythrocytes, saliva, and urine; ionized magnesium concentrations in blood, plasma, or serum; and magnesium-loading tests. However, no single method is entirely satisfactory [7]. Comprehensive evaluation may require both lab tests and clinical assessment [6].
Recommended Magnesium Intake
The Food and Nutrition Board (FNB) at the Institute of Medicine of the National Academies has established Dietary Reference Intakes (DRIs) for magnesium and other nutrients [1]. DRIs are reference values used for planning and assessing nutrient intakes of healthy individuals. These values vary by age and sex and include the Recommended Dietary Allowance (RDA), Adequate Intake (AI), Estimated Average Requirement (EAR), and Tolerable Upper Intake Level (UL). The RDA represents the average daily intake level sufficient to meet the nutrient requirements of nearly all healthy individuals (97%–98%), while the AI is established when evidence is insufficient to develop an RDA. The EAR is the average daily intake level estimated to meet the requirements of 50% of healthy individuals. The UL represents the maximum daily intake unlikely to cause adverse health effects.
The RDAs for magnesium vary depending on age and sex. For adults, the RDA ranges from 400 mg to 420 mg for men and 310 mg to 320 mg for women. During pregnancy, the RDA increases slightly to 350 mg to 360 mg.
Sources of Magnesium
Magnesium is prevalent in various foods and beverages. Good sources include green leafy vegetables, legumes, nuts, seeds, and whole grains [1,3]. Generally, foods high in dietary fiber also contain magnesium. Some breakfast cereals and fortified foods also have added magnesium. Food processing, like refining grains, can significantly reduce magnesium content [1]. Tap, mineral, and bottled waters can also contribute to magnesium intake, but the amount varies by source and brand [8]. The body typically absorbs about 30% to 40% of dietary magnesium [2,9].
Magnesium Supplements
Magnesium supplements come in various forms, including magnesium oxide, citrate, and chloride [2,3]. The Supplement Facts panel indicates the amount of elemental magnesium, not the entire compound’s weight. Absorption varies among different forms; magnesium that dissolves well in liquid is more completely absorbed [2,12]. Studies suggest that magnesium aspartate, citrate, lactate, and chloride are more bioavailable than magnesium oxide and magnesium sulfate [12-16]. High doses of zinc supplements (142 mg/day) can interfere with magnesium absorption [17].
Magnesium in Medications
Magnesium is a key ingredient in some laxatives. For example, Phillips’ Milk of Magnesia provides 500 mg of elemental magnesium (as magnesium hydroxide) per tablespoon [19]. It is also found in some remedies for heartburn and upset stomach due to acid indigestion [18].
How Much Magnesium is Too Much? Understanding the Upper Limits
While magnesium is essential, exceeding the Tolerable Upper Intake Level (UL) can lead to adverse effects. The UL for supplemental magnesium is set at 350 mg per day for adults. This limit applies to magnesium from supplements and medications only, not from food sources [1]. The kidneys effectively eliminate excess magnesium from food in healthy individuals [29].
Health Risks of Excessive Magnesium
Consuming too much magnesium from supplements or medications can cause diarrhea, often accompanied by nausea and abdominal cramping [1]. Magnesium carbonate, chloride, gluconate, and oxide are commonly reported to cause diarrhea [12]. The laxative effect is due to the osmotic activity of unabsorbed salts in the intestine and colon, and the stimulation of gastric motility [57].
Very high doses of magnesium-containing laxatives and antacids (typically exceeding 5,000 mg/day) have been linked to magnesium toxicity [58], including fatal hypermagnesemia [59,60]. Symptoms of magnesium toxicity, which usually manifest when serum concentrations exceed 1.74–2.61 mmol/L, can include hypotension, nausea, vomiting, facial flushing, urine retention, ileus, depression, and lethargy. These can progress to muscle weakness, breathing difficulties, extreme hypotension, irregular heartbeat, and cardiac arrest [29]. Impaired renal function or kidney failure increases the risk of magnesium toxicity because it reduces the ability to eliminate excess magnesium [1,29].
Table 3: Tolerable Upper Intake Levels (ULs) for Supplemental Magnesium [1]
| Age | Male | Female | Pregnant | Lactating |
|—|—|—|—|—|
| Birth to 12 months | None established | None established |
| 1–3 years | 65 mg | 65 mg |
| 4–8 years | 110 mg | 110 mg |
| 9–18 years | 350 mg | 350 mg | 350 mg | 350 mg |
| 19+ years | 350 mg | 350 mg | 350 mg | 350 mg |
Interactions with Medications
Magnesium supplements can interact with certain medications, affecting their absorption or magnesium status. Bisphosphonates, used to treat osteoporosis, should be taken at least 2 hours apart from magnesium-rich supplements [57]. Similarly, tetracycline and quinolone antibiotics should be taken 2 hours before or 4–6 hours after a magnesium-containing supplement [57,62]. Loop and thiazide diuretics can increase magnesium loss in urine, while potassium-sparing diuretics reduce magnesium excretion [63]. Prolonged use of proton pump inhibitors (PPIs) can lead to hypomagnesemia [64].
Conclusion
Magnesium is crucial for maintaining various bodily functions, but it’s essential to be aware of the potential risks of excessive intake. While magnesium from food is generally safe, high doses from supplements and medications can lead to adverse effects, including diarrhea and, in rare cases, magnesium toxicity. Adhering to the established Tolerable Upper Intake Levels (ULs) for supplemental magnesium is crucial to prevent health risks. Individuals with impaired renal function or those taking medications that interact with magnesium should exercise caution and consult with a healthcare provider to determine appropriate magnesium intake levels.
References
The references are the same as the original article, so they are not repeated here for brevity. Please refer to the original article for the full list of references.
