Magnesium citrate and magnesium glycinate are two commonly available forms of magnesium supplements, each with distinct properties that may influence their suitability for individual needs. Whilst both provide essential magnesium—a mineral involved in over 300 enzymatic reactions including muscle function, nerve transmission, and bone health—they differ in bioavailability, gastrointestinal tolerability, and potential applications. Understanding these differences can help individuals and healthcare professionals make informed decisions about supplementation. This article examines the key distinctions between magnesium citrate and glycinate, their absorption profiles, safety considerations, and guidance on selecting the most appropriate form based on individual circumstances and clinical needs.

What Are Magnesium Citrate and Magnesium Glycinate?

Magnesium is an essential mineral involved in over 300 enzymatic reactions in the human body, including energy production, protein synthesis, muscle and nerve function, and bone health. The UK Reference Nutrient Intake (RNI) for magnesium is 300 mg daily for men and 270 mg daily for women. National Diet and Nutrition Survey data suggest that some adults in the UK do not meet these recommendations through diet alone, leading some individuals to consider supplementation.

Magnesium citrate is a compound formed by combining elemental magnesium with citric acid. This salt is highly soluble in water and is available as a dietary supplement. In higher doses, it can have an osmotic laxative effect and is sometimes used in bowel preparation formulations. The citrate component enhances the solubility of magnesium in the gastrointestinal tract. Magnesium citrate is available in tablet, capsule, and powder formulations.

Magnesium glycinate consists of magnesium bound to the amino acid glycine. This chelated form is recognised for its generally good bioavailability and typically gentler effect on the digestive system. Glycine itself has inhibitory neurotransmitter properties, though evidence for additional benefits from the glycine component in magnesium glycinate supplements is limited. Magnesium glycinate is less likely to cause gastrointestinal side effects such as diarrhoea compared to some other magnesium salts, potentially making it suitable for individuals with sensitive digestive systems.

Both forms provide supplemental magnesium but differ in their properties, tolerability, and potential applications. The elemental magnesium content varies between products and formulations, so it's important to check product labels for the actual amount of elemental magnesium provided per dose rather than the total compound weight.

Key Differences Between Magnesium Citrate and Glycinate

The primary differences between magnesium citrate and magnesium glycinate relate to their bioavailability, gastrointestinal effects, and potential applications. These distinctions may influence which formulation might be more appropriate for individual needs.

Elemental magnesium content varies between the two forms and between different product formulations. Magnesium citrate typically contains approximately 11-16% elemental magnesium by weight, depending on its hydration state, whereas magnesium glycinate generally contains around 14%. This means that a 500 mg tablet of magnesium citrate might provide roughly 55-80 mg of elemental magnesium, whilst the same weight of magnesium glycinate might yield approximately 70 mg. It is essential to check product labels for the stated elemental magnesium content rather than relying on total compound weight when comparing supplements.

Gastrointestinal tolerability represents a notable difference. Magnesium citrate has an osmotic effect, drawing water into the intestinal lumen, which can promote bowel movements. This property may cause loose stools or diarrhoea, particularly at higher doses. In contrast, magnesium glycinate is chelated to glycine, which appears to reduce its osmotic effect in the intestine, potentially making it gentler on the digestive system. This characteristic may make glycinate more suitable for individuals who experience digestive discomfort with other magnesium forms.

Potential applications also differ. Magnesium citrate's osmotic properties mean it may affect bowel habits, though it is not recommended as a first-line treatment for chronic constipation in the UK (where macrogols are preferred). Magnesium glycinate, with its typically milder effect on bowel function, may be considered when supplementation is desired without affecting bowel habits. Some individuals report benefits with magnesium glycinate for muscle relaxation or sleep, though robust clinical evidence for superior efficacy compared to other magnesium forms for these specific purposes remains limited.

Which Form of Magnesium Is Better for Absorption?

Bioavailability—the proportion of an administered dose that reaches systemic circulation—is an important consideration when comparing magnesium supplements. Research indicates that both magnesium citrate and magnesium glycinate generally demonstrate better absorption compared to less soluble forms such as magnesium oxide.

Studies examining magnesium absorption have shown that organic salts (including citrate) and chelated forms (such as glycinate) are typically better absorbed than inorganic forms. A study published in the Journal of the American College of Nutrition found that magnesium citrate had significantly higher bioavailability than magnesium oxide. Chelated forms like magnesium glycinate have also demonstrated good absorption profiles, though direct head-to-head comparisons between citrate and glycinate are limited, making definitive statements about superiority difficult.

The mechanism of absorption may differ between these forms. Magnesium citrate's water solubility facilitates passive diffusion across the intestinal mucosa. The citrate component may also enhance absorption by forming soluble complexes. Magnesium glycinate, being bound to an amino acid, may potentially utilise both magnesium transport pathways and amino acid transport mechanisms, though this theoretical advantage requires further research confirmation.

Individual factors significantly influence magnesium absorption regardless of the form chosen. Gastrointestinal health, stomach acid levels, concurrent medications, and dietary factors all affect bioavailability. Proton pump inhibitors (PPIs) and H2-receptor antagonists may reduce magnesium absorption. The MHRA has issued a Drug Safety Update highlighting that long-term use of PPIs has been associated with hypomagnesaemia through mechanisms that may extend beyond gastric pH effects. Patients with inflammatory bowel disease, coeliac disease, or other malabsorption conditions may have impaired magnesium uptake from any oral source.

From a practical standpoint, both magnesium citrate and glycinate are considered well-absorbed forms in individuals with normal gastrointestinal function. The choice between them should therefore be guided primarily by individual tolerability and specific needs rather than absorption differences alone.

Choosing Between Magnesium Citrate and Glycinate for Your Needs

Selecting an appropriate magnesium supplement requires consideration of individual health status, specific needs, and potential adverse effects. Healthcare professionals can provide personalised guidance based on clinical assessment.

Magnesium citrate may be considered when:

• Mild constipation is also present – Though not a first-line treatment for chronic constipation in the UK (where macrogols are preferred)

• Cost is a consideration – Magnesium citrate is often widely available

• Short-term supplementation is planned – The potential laxative effect may be acceptable for brief courses

Magnesium glycinate may be more suitable when:

• Gastrointestinal sensitivity exists – Individuals prone to diarrhoea or with irritable bowel syndrome may better tolerate glycinate

• Long-term supplementation is required – Better tolerability may support adherence to ongoing therapy

• Minimal effect on bowel habits is desired – For those seeking magnesium supplementation without changes to bowel function

Safety considerations apply to both forms. Patients with chronic kidney disease should consult their GP or nephrologist before taking magnesium supplements, as impaired renal excretion may lead to hypermagnesaemia. Symptoms of magnesium excess include nausea, diarrhoea, hypotension, muscle weakness, and in severe cases, cardiac arrhythmias. The UK safe upper level for supplemental magnesium (not including dietary sources) is 400 mg daily for adults, with diarrhoea often being the dose-limiting effect.

Drug interactions warrant attention. Magnesium can reduce absorption of certain medications:

• Tetracyclines and quinolone antibiotics: separate by at least 2 hours before or 4-6 hours after magnesium

• Bisphosphonates: follow specific timing instructions in the patient information leaflet

• Levothyroxine: separate by at least 4 hours

• Iron supplements: take at different times of day

Concurrent use with diuretics requires monitoring; loop and thiazide diuretics may increase magnesium loss, while potassium-sparing diuretics may reduce excretion.

When to seek medical advice: Patients should contact their GP if they experience persistent symptoms suggestive of magnesium deficiency (muscle cramps, fatigue, abnormal heart rhythms) or if supplementation does not improve symptoms within 4-6 weeks. Those with existing medical conditions, particularly renal impairment, cardiac disease, or diabetes, should discuss supplementation with their healthcare provider before starting. Pregnant or breastfeeding women should also seek professional guidance.

Urgent medical attention is needed for chest pain, severe palpitations, fainting, or symptoms of severe magnesium deficiency. For constipation, red flags requiring prompt assessment include rectal bleeding, unexplained weight loss, or persistent change in bowel habit.

Suspected adverse reactions to magnesium supplements can be reported through the MHRA Yellow Card scheme (yellowcard.mhra.gov.uk).

Ultimately, there is no universally superior choice between magnesium citrate and glycinate. The optimal selection depends on individual circumstances, tolerability, and specific needs. Healthcare professionals can support patients in making informed decisions by considering these factors alongside dietary magnesium intake and any underlying health conditions.

Frequently Asked Questions