Magnesium: What It Is and How It Works

Magnesium is one of the most important minerals in the human body, involved in hundreds of biochemical reactions, yet many Americans fall short of recommended intakes. Our editorial team explains what magnesium does, why it matters for athletes in particular, how to recognize low intake, and how to choose a supplement if diet is not enough.

What magnesium is and where it lives in the body

Magnesium is an essential dietary mineral, meaning the body cannot make it and must obtain it from food. An adult body contains roughly 25 grams of magnesium. About 60 percent is stored in bone, with most of the rest inside muscle and soft tissue, and only about one percent circulating in the blood.

Because so little magnesium is in the blood, a standard blood test is not a reliable measure of total body stores. Someone can have normal serum magnesium while still being depleted, which complicates diagnosis of low magnesium status.

Magnesium acts as a cofactor, a helper molecule, for more than 300 enzyme systems. These include reactions that produce and use ATP, the body's energy currency, which is why magnesium is sometimes described as central to cellular energy.

The mineral also helps stabilize the structure of DNA and RNA and regulates the transport of other ions such as calcium and potassium across cell membranes, placing it at the heart of many physiological processes.

How magnesium works in muscle and nerves

One of magnesium's most relevant roles for athletes is in muscle contraction and relaxation. Calcium triggers muscle fibers to contract, and magnesium acts as a natural counterbalance that allows them to relax. An imbalance can contribute to muscle twitching and cramps.

Magnesium is also essential for nerve signaling. It modulates receptors in the nervous system, including the NMDA receptor, which influences how nerve cells communicate. This is part of why severe magnesium deficiency can cause neuromuscular symptoms.

In energy metabolism, ATP must bind magnesium to become biologically active; the usable form is technically Mg-ATP. Every energy-requiring process, from muscle work to protein synthesis, therefore depends on adequate magnesium.

Magnesium contributes to electrolyte balance alongside sodium, potassium and calcium. During prolonged exercise and heavy sweating, electrolyte losses can shift these balances, which is one reason athletes pay attention to the mineral.

Signs of low intake and who is at risk

Outright magnesium deficiency is uncommon in healthy people, but suboptimal intake is widespread. US dietary surveys suggest a large share of adults consume less than the recommended amount, largely because diets low in whole grains, nuts and leafy greens are low in magnesium.

Early signs of low magnesium can be vague: fatigue, muscle cramps, poor sleep and irritability. More severe deficiency can cause numbness, abnormal heart rhythms and low blood calcium or potassium, but these are typically seen in medical conditions rather than mild dietary shortfall.

Several groups are at higher risk. These include people with gastrointestinal disorders that impair absorption, those with type 2 diabetes, heavy alcohol users, older adults, and people taking certain medications such as some diuretics and proton-pump inhibitors.

Athletes may have modestly higher needs because of magnesium losses in sweat and urine, and because strenuous training increases the demand on energy metabolism. However, this does not automatically mean supplements are required.

• Low intake of whole grains, nuts, seeds and leafy greens.
• Gastrointestinal disorders affecting absorption.
• Type 2 diabetes or insulin resistance.
• Heavy alcohol consumption.
• Certain medications, including some diuretics and acid reducers.

Food sources, forms and supplementation

The best approach for most people is food first. Rich dietary sources include pumpkin seeds, almonds, spinach, black beans, whole grains, dark chocolate and avocado. Building these into regular meals usually covers requirements without supplements.

The Recommended Dietary Allowance in the US is about 400–420 mg per day for adult men and 310–320 mg for adult women, with higher needs during pregnancy. These figures come from the National Academies and reflect total intake from food and supplements combined.

If supplementation is warranted, the form matters for tolerability and absorption. Magnesium oxide is cheap but poorly absorbed and more likely to cause loose stools; magnesium citrate, glycinate and malate are generally better tolerated and absorbed.

The Tolerable Upper Intake Level for supplemental magnesium is 350 mg per day for adults, a limit that applies to supplements, not food. Exceeding it commonly causes diarrhea, and very high doses can be dangerous for people with kidney disease.

Magnesium, performance and sleep

The evidence that magnesium supplements improve athletic performance in people who already have adequate intake is weak. The clearest benefits appear when correcting a true shortfall, where restoring magnesium can relieve cramps, fatigue and poor sleep.

Some research suggests magnesium supports sleep quality and may help with symptoms of stress, though the effects are modest and the studies are mixed. For athletes, better sleep indirectly supports recovery and performance.

For muscle cramps, magnesium is often recommended anecdotally, but controlled trials have not strongly supported supplements for exercise-associated cramps in people with normal status. Hydration and conditioning remain more important.

The sensible strategy is to prioritize magnesium-rich foods, consider a well-tolerated supplement if intake is low or symptoms suggest a shortfall, and avoid megadoses, which cause digestive upset without added benefit.

Our Editorial Conclusions

Magnesium is a foundational mineral for energy production, muscle relaxation and nerve function. Many people fall short of recommended intakes, and athletes may have slightly higher needs.

Food should be the first line, with nuts, seeds, leafy greens, legumes and whole grains doing most of the work. A well-chosen supplement can help when diet is insufficient, but staying within the 350 mg supplemental upper limit avoids digestive problems.

Supplements are most useful for correcting a deficiency rather than boosting performance in well-nourished athletes, and people with kidney disease should consult a doctor before supplementing.

For related reading, our editors suggest articles on electrolytes and hydration during training, on how sleep affects recovery, and on zinc and other minerals relevant to athletes.

References

1. Institute of Medicine. Dietary Reference Intakes for Calcium, Phosphorus, Magnesium, Vitamin D, and Fluoride. Washington, DC: National Academies Press; 1997.
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4. Zhang Y, Xun P, Wang R, et al. Can magnesium enhance exercise performance? Nutrients. 2017;9(9):946.
5. Rosanoff A, Weaver CM, Rude RK. Suboptimal magnesium status in the United States: are the health consequences underestimated? Nutr Rev. 2012;70(3):153–164.
6. National Institutes of Health, Office of Dietary Supplements. Magnesium: fact sheet for health professionals. Bethesda, MD; 2022.