Magnesium citrate vs glycinate is a common question for those considering magnesium supplementation. Both are highly bioavailable organic forms of this essential mineral, which supports over 300 enzymatic reactions including muscle function, nerve transmission, and bone health. The key difference lies in gastrointestinal tolerability: magnesium citrate has mild laxative properties, whilst magnesium glycinate is chelated to amino acids and typically causes fewer digestive side effects. Understanding these distinctions helps patients and healthcare professionals select the most appropriate formulation based on individual needs, tolerability, and therapeutic goals. Both supplements are widely available in the UK as food supplements.

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. While the National Diet and Nutrition Survey (NDNS) suggests some UK adults have intakes below the RNI, this doesn't necessarily indicate deficiency.

Magnesium citrate is a compound formed by combining elemental magnesium with citric acid. This salt is highly soluble in water and is available both as a dietary supplement and, in higher doses, as an osmotic laxative. The citrate component enhances the solubility of magnesium in the gastrointestinal tract, potentially facilitating its absorption. Magnesium citrate is available in tablet, capsule, and powder formulations and may be used for individuals with constipation, though in the UK, macrogols (polyethylene glycol) are typically recommended as first-line treatments for constipation.

Magnesium glycinate (also known as magnesium bisglycinate) consists of magnesium bound to two molecules of the amino acid glycine. This chelated form is designed to enhance absorption whilst minimising gastrointestinal side effects. Glycine itself has been studied for potential calming properties, though evidence for significant effects at the doses present in magnesium glycinate supplements is limited. Magnesium glycinate is frequently chosen by individuals seeking to support nervous system function or address magnesium deficiency without the laxative effects associated with other forms.

Both supplements are available over the counter in the UK, primarily as food supplements regulated by the Food Standards Agency rather than as licensed medicines, and are generally considered safe when used at recommended doses.

Key Differences Between Magnesium Citrate and Glycinate

The primary differences between magnesium citrate and magnesium glycinate relate to their bioavailability, gastrointestinal effects, and clinical applications. Understanding these distinctions can help patients and healthcare professionals select the most appropriate formulation for individual needs.

Gastrointestinal tolerability represents the most clinically significant difference. Magnesium citrate has an osmotic effect in the bowel, drawing water into the intestinal lumen and promoting bowel movements. This property may cause loose stools or diarrhoea, particularly at higher doses (typically above 400 mg elemental magnesium daily). In contrast, magnesium glycinate is chelated to amino acids, which appears to reduce its osmotic activity. Clinical experience suggests it is better tolerated by individuals with sensitive digestive systems and is less likely to cause diarrhoea at therapeutic doses.

Elemental magnesium content also differs between formulations. Magnesium citrate typically contains approximately 16% elemental magnesium by weight, whilst magnesium glycinate contains approximately 14%, though this can vary by specific product formulation. This means that a 500 mg tablet of magnesium citrate provides roughly 80 mg of elemental magnesium, whereas the same weight of magnesium glycinate provides about 70 mg. Patients should always check product labels for elemental magnesium content rather than total compound weight.

Clinical applications may guide selection based primarily on tolerability rather than proven efficacy differences. Magnesium citrate may cause looser stools, which some individuals find beneficial if they experience constipation. Magnesium glycinate is frequently chosen for chronic supplementation, particularly by those with sensitive digestive systems. While some suggest magnesium glycinate may be preferable for symptoms such as muscle cramps, anxiety, or sleep disturbance, robust clinical evidence establishing superiority for these specific conditions is currently limited.

Which Form of Magnesium Is Better for Absorption?

Bioavailability—the proportion of ingested magnesium that reaches systemic circulation—is a critical consideration when comparing supplement forms. Research suggests that organic magnesium salts (including both citrate and glycinate) generally demonstrate superior absorption compared to inorganic forms such as magnesium oxide.

Studies examining magnesium absorption have shown that magnesium citrate and magnesium glycinate both exhibit good bioavailability, though direct comparative data are limited. A frequently cited study published in the Journal of the American College of Nutrition found that magnesium citrate was more bioavailable than magnesium oxide, with significantly higher serum magnesium levels following supplementation. Similarly, research on chelated magnesium forms, including glycinate, suggests enhanced absorption due to the protective effect of amino acid binding, which may facilitate transport across the intestinal mucosa, though the exact mechanisms in humans require further research.

The mechanism of absorption differs slightly between these forms. Magnesium citrate dissolves readily in the acidic environment of the stomach, releasing free magnesium ions that are absorbed primarily in the small intestine via both passive diffusion and active transport mechanisms. Magnesium glycinate, being chelated, may be absorbed partially intact through peptide transport pathways, potentially bypassing some of the competitive inhibition that affects free magnesium ion absorption, though this mechanism is not definitively established in humans.

It's worth noting that serum magnesium is not always a reliable indicator of total body magnesium status due to tight homeostatic regulation, with only 1% of total body magnesium being present in the bloodstream.

Individual factors significantly influence magnesium absorption regardless of supplement form. These include:

• Gastric acid production: Reduced stomach acid (common in older adults or those taking proton pump inhibitors) may impair dissolution of some magnesium salts

• Intestinal health: Conditions such as inflammatory bowel disease or coeliac disease can reduce absorption

• Dietary factors: High intake of fibre, phytates, or calcium may compete with magnesium absorption

• Dose: Fractional absorption decreases as dose increases; smaller divided doses are absorbed more efficiently than single large doses

For practical purposes, both magnesium citrate and glycinate are considered highly bioavailable forms. The choice between them should be guided primarily by tolerability and individual response rather than absorption differences alone.

Choosing Between Magnesium Citrate and Glycinate for Your Needs

Selecting the appropriate magnesium supplement requires consideration of individual symptoms, tolerability, and therapeutic goals. Both magnesium citrate and glycinate are effective options, but specific clinical scenarios may favour one over the other.

Consider magnesium citrate if:

• You have normal bowel function and can tolerate potential mild laxative effects

• Cost is a primary consideration, as citrate formulations are often less expensive

Consider magnesium glycinate if:

• You have a sensitive digestive system or history of diarrhoea with other magnesium supplements

• You require long-term supplementation and prioritise gastrointestinal comfort

Dosing considerations: The NHS advises that adults should not exceed 400 mg of elemental magnesium daily from supplements, as higher doses may cause diarrhoea and abdominal cramping. When initiating supplementation, start with lower doses (100–200 mg elemental magnesium daily) and increase gradually based on tolerance and response. Dividing the daily dose (e.g., taking half in the morning and half in the evening) may improve both absorption and tolerability.

Safety and interactions: Both forms are generally well tolerated, but patients should be aware of potential interactions. Magnesium supplements can reduce absorption of certain medications including:

• Antibiotics (tetracyclines, quinolones): separate by at least 4 hours

• Bisphosphonates: separate by at least 2 hours

• Levothyroxine: separate by at least 4 hours

• Iron supplements: separate by at least 2 hours

• Antivirals (particularly integrase inhibitors like dolutegravir): separate by at least 4 hours

If you take multiple medications, consult your pharmacist for specific advice on timing.

Individuals with renal impairment should consult their GP before supplementing, as reduced kidney function impairs magnesium excretion and may lead to hypermagnesaemia.

When to seek medical advice: Contact your GP if you experience persistent symptoms despite supplementation, develop signs of magnesium toxicity (muscle weakness, confusion, irregular heartbeat), or if you have underlying kidney disease, heart conditions, or take multiple medications. Documented magnesium deficiency (serum magnesium typically <0.7 mmol/L, though reference ranges vary between laboratories) should be investigated for underlying causes such as malabsorption, chronic diarrhoea, or medication effects (particularly diuretics and proton pump inhibitors). Symptomatic or severe hypomagnesaemia may require intravenous replacement under medical supervision according to hospital protocols, particularly if associated with cardiac arrhythmias or severe symptoms.

If you experience any suspected adverse reactions to magnesium supplements, report them through the MHRA Yellow Card scheme.

Frequently Asked Questions