Magnesium Guide: What It Does, Food Sources and Supplement Forms

What is magnesium?

Magnesium is an essential mineral involved in hundreds of processes throughout the body. It supports both aerobic and anaerobic energy production, assists with glycolysis, activates enzymes, and forms part of the Mg-ATP complex that allows cells to use energy. Magnesium is also required for healthy mitochondrial function and oxidative phosphorylation. In addition, it helps regulate potassium movement and calcium metabolism [1].

Magnesium is the second most abundant ion within our cells and the fourth most abundant ion in the human body. A healthy adult is estimated to contain approximately 20–28 g of magnesium. Around 50%–60% is stored in bone, 34%–39% is found in muscles, soft tissues and organs, and only 1%–2% is present in the blood and extracellular fluids [2].

In the blood, magnesium exists in three main forms. Approximately 55%–70% is free or ionised, 20%–30% is bound to proteins, and 5%–15% is bound to substances such as phosphate, citrate and bicarbonate [3]. Free ionised magnesium is considered the biologically active form and takes part in many enzymatic reactions and physiological processes [2,4].

Magnesium is found in a wide range of plant and animal foods. Green vegetables, legumes, peas, nuts, shellfish and spices are particularly rich sources. Unrefined cereals can also provide magnesium, while highly refined flours, many tubers and fruits, oils and fats generally contribute much less [1].

The amount of magnesium absorbed from food can vary considerably. Absorption may range from approximately 25% when dietary magnesium intake is high to 75% when intake is low [1]. The kidneys, intestines and bones work together to tightly regulate magnesium balance, or homeostasis, within the body [2,5].

Magnesium absorption is not a single or straightforward process. Its absorption and bioavailability can be influenced by several dietary and physiological factors [6]. Phytates, oxalates, fibre, alcohol, and excessive amounts of phosphate or calcium may reduce the amount absorbed [6].

What does magnesium do in the body?

Energy generation

Magnesium is essential for energy metabolism and production. It binds to ATP to form Mg-ATP, making the body's main energy currency biologically usable. This supports phosphorylation reactions, activates enzymes involved in glycolysis and related pathways, and helps mitochondria produce energy efficiently [6–8].

When magnesium is low, the body may produce and use energy less efficiently. This is associated with fatigue, weakness, reduced exercise efficiency and some forms of metabolic dysfunction [9–11].

Muscles and nerves

Magnesium plays a stabilising and regulatory role in both muscles and nerves. It helps nerves transmit signals normally and supports muscle contraction and relaxation by regulating cell excitability and the movement of calcium, sodium and potassium across cell membranes [1,12].

Magnesium also helps prevent excessive nerve and muscle stimulation by moderating excitatory neurotransmitter activity, including activity at NMDA receptors and the neuromuscular junction [12,13].

When magnesium levels are low, nerves and muscles may become more irritable. This can contribute to symptoms such as cramps, twitching, weakness and spasms [3,13]. However, these symptoms can be difficult to interpret because magnesium deficiency may occur alongside low calcium or potassium levels. If symptoms persist, seek advice from an appropriate healthcare professional.

Bones

The broad physiological importance of magnesium and its positive association with bone density are strongly supported. Magnesium helps support bone mineralisation and mineral regulation, including pathways involving parathyroid hormone and vitamin D-related metabolism. In human studies, higher intake is generally associated with higher bone mineral density [14–16].

Magnesium-rich foods

Plant foods are among the most reliable practical magnesium sources for Australian consumers, particularly legumes and pulses, leafy vegetables, nuts, seeds and wholegrain cereal foods [1,17].

Table source: Adapted from Healthdirect Australia's “Foods high in magnesium” resource, which presents common foods and their magnesium content using data sourced from the Australian Food Composition Database. Magnesium content can vary by food variety, processing method, serving size and brand [17].

How much magnesium do you need?

In Australia, the Recommended Dietary Intake (RDI) for magnesium is 310–320 mg per day for adult women and 400–420 mg per day for adult men, depending on age. These amounts refer to total magnesium intake from food and supplements combined [1].

What can affect magnesium intake or status?

Magnesium status can vary considerably between individuals. It depends on how much magnesium is consumed, how much is absorbed by the intestines, and how much is retained by the kidneys [1,3,5,18,19].

Each of these factors can be influenced by current magnesium stores, health conditions, medications and other individual circumstances.

Diet pattern and food processing

Whole grains, legumes, nuts, vegetables and magnesium-rich mineral water can support magnesium intake [20]. In contrast, highly refined and Western-style dietary patterns may provide less magnesium, as food processing can remove a large proportion of the magnesium naturally present in grains [21,22].

Absorption conditions in the gut

The amount of magnesium absorbed by the intestines is influenced by the dose consumed, the foods eaten alongside it, and the health of the digestive system [23]. Phytates and some insoluble fibres may reduce absorption, while certain fermentable fibres and carbohydrates may improve it [23–25].

Kidney function

Healthy kidneys help maintain magnesium balance by reducing urinary losses when intake is low [2,3,5]. However, diabetes, inherited kidney disorders, changes in acid-base balance, and some medications can increase magnesium loss through the urine [18].

Medications

Certain medications can affect magnesium status in different ways. Proton pump inhibitors (PPIs) are associated with reduced intestinal magnesium absorption, while medications such as cisplatin, aminoglycoside antibiotics and some diuretics may increase magnesium loss through the kidneys [18,26–28].

Health and life stage

Diabetes, gastrointestinal disease, malabsorption, alcohol dependence, pregnancy-related conditions, older age and kidney disease may affect magnesium intake, absorption, retention, or how magnesium results are interpreted [2,29,30].

Measuring magnesium status

Serum magnesium is convenient to measure but does not always reflect the body's total magnesium stores. A normal serum result may therefore not completely rule out low magnesium status. In some circumstances, urine tests, fractional magnesium excretion, intracellular markers or magnesium-loading tests may provide additional information [29,31,32].

Magnesium status is therefore not determined by intake alone; it also depends on how well the body absorbs, retains and regulates it.

Types of magnesium supplements

There are several forms of magnesium available in supplements. Some forms contain a higher proportion of elemental magnesium, while others may differ in solubility, gastrointestinal tolerability and supporting evidence.

One of the simplest ways to understand which form of magnesium you are taking is to read the ingredient panel on the product label.

Magnesium oxide

Several naturally derived magnesium supplements use magnesium oxide. This form tends to contain a high percentage of elemental magnesium and is therefore sometimes used to increase the amount of magnesium provided within a formulation.

Several studies indicate that magnesium oxide may be less well tolerated at higher doses [33,34].

Magnesium glycinate

Magnesium glycinate combines magnesium with glycine, an amino acid. Over the years, it has become one of the more popular forms of supplemental magnesium, including because of its gastrointestinal tolerability [35].

As demand has grown, manufacturers have developed different forms of magnesium glycinate and different approaches to increasing elemental magnesium content. In some formulations this can involve “buffering” the product with other magnesium compounds, such as magnesium oxide.

For greater clarity and transparency, look for the more specific term magnesium bisglycinate, or, in Australia, a fully defined ingredient form such as magnesium glycinate dihydrate. More precise ingredient descriptions provide greater information about the compound being used and reduce ambiguity around the degree of chelation.

Magnesium amino acid chelate

Magnesium amino acid chelate combines magnesium with amino acids. Chelation of magnesium alongside amino acids may support gastrointestinal tolerability [33].

Magnesium citrate

Human studies have demonstrated that magnesium citrate is an effective and bioavailable source of supplemental magnesium and may provide greater magnesium absorption than less soluble inorganic forms such as magnesium oxide [36–38]. A systematic review of magnesium supplementation similarly concluded that organic magnesium forms generally tend to demonstrate greater bioavailability than inorganic forms [38].

Citrate is a naturally occurring intermediate in cellular energy metabolism and an integral component of the citric acid cycle.

At higher supplemental doses, magnesium citrate may produce a laxative effect in some individuals due primarily to the osmotic activity of unabsorbed magnesium within the gastrointestinal tract. However, this effect is dose- and individual-dependent and is not an inevitable consequence of magnesium citrate supplementation [38].

Appropriately controlled doses may improve gastrointestinal tolerability by limiting the amount of unabsorbed magnesium present in the intestine at any one time. Fractional magnesium absorption also tends to decrease as the amount of magnesium consumed per dose increases [3,23].

Overall, magnesium citrate is a well-established and widely used form of magnesium suitable for ongoing supplementation [39].

Other magnesium forms

Other magnesium forms include magnesium L-threonate, aspartate, diglutamate, ascorbyl phosphate, glycerophosphate, lysinate and orotate. Each has distinct chemical characteristics and potential properties.

The molecule paired with magnesium can influence factors such as solubility, elemental magnesium content, gastrointestinal tolerability and potentially absorption. However, its normal biochemical role does not automatically confer a unique therapeutic effect on the magnesium compound.

The strength of evidence also varies considerably between forms. Magnesium aspartate has human bioavailability data demonstrating relatively good absorption, while magnesium L-threonate has emerging human research investigating outcomes such as sleep and cognition.

In contrast, evidence for forms such as magnesium diglutamate, glycerophosphate, lysinate, orotate and ascorbyl phosphate is more limited, formulation-dependent or predominantly preclinical [15,18,39–43].

While each form may offer formulation-specific advantages, the available evidence should be considered individually rather than assuming that the properties of the attached molecule translate directly into additional clinical benefits.

How to choose a magnesium supplement?

When considering a magnesium supplement, there is no single form that is necessarily right for everyone.

Different forms vary in their chemical structure, elemental magnesium content, solubility, gastrointestinal tolerability and supporting evidence. Individual requirements may also differ according to dietary intake, life stage, health status and other factors.

Food should remain the foundation of magnesium intake, while supplementation can be considered where appropriate as part of a balanced diet and lifestyle.

When comparing products, read the ingredient panel carefully, consider both the form of magnesium and the amount of elemental magnesium provided, and seek advice from an appropriate healthcare professional if you are unsure which approach is suitable for you.