Magnesium citrate and magnesium glycinate are two popular forms of magnesium supplements available in the UK, each with distinct properties that may suit different individuals. Magnesium is essential for over 300 bodily processes, including muscle function, nerve transmission, and bone health. Whilst both forms are well absorbed compared to inorganic alternatives, they differ in gastrointestinal tolerability and elemental magnesium content. Understanding these differences can help you select the most appropriate supplement for your needs, whether you prioritise digestive comfort or cost-effectiveness. This article examines the key distinctions between magnesium citrate and glycinate to support informed decision-making.

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. The National Diet and Nutrition Survey (NDNS) suggests that some UK adults may not meet these recommendations through diet alone, which has led to interest in 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 and specific formulations, it is used as an osmotic laxative, primarily in bowel preparation before certain medical procedures rather than for routine constipation management. The citrate component enhances the solubility of magnesium in the gastrointestinal tract. Magnesium citrate is available in tablet, capsule, and powder formulations.

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 potentially causing fewer gastrointestinal side effects. Some suggest that glycine itself may have calming properties, though clinical evidence for this synergistic benefit is limited. Magnesium glycinate is often marketed for those seeking to support general magnesium levels with reduced likelihood of digestive disturbances.

Both supplements are available over the counter in the UK and are generally considered safe when used at recommended doses. Women who are pregnant or breastfeeding should consult a healthcare professional before taking magnesium supplements.

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. Understanding these distinctions can help patients and healthcare professionals select the most appropriate formulation for individual needs.

Gastrointestinal tolerability represents a notable difference. Magnesium citrate has an osmotic effect in the bowel, drawing water into the intestinal lumen and potentially 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 may be better tolerated by some individuals with sensitive digestive systems, though comparative studies are limited.

Elemental magnesium content also differs between formulations. The percentage of elemental magnesium varies by specific salt form and hydration state. As a general guide, magnesium citrate typically contains approximately 16% elemental magnesium by weight, whilst magnesium glycinate contains approximately 14%. This means that a 500 mg tablet of magnesium citrate might provide roughly 80 mg of elemental magnesium, whereas the same weight of magnesium glycinate might provide about 70 mg. Patients should always check product labels for elemental magnesium content rather than total compound weight.

Potential applications may influence selection. In the UK, high-dose magnesium citrate formulations are primarily used in bowel preparation under medical supervision rather than for routine constipation (where macrogols are the first-line treatment according to NICE Clinical Knowledge Summaries). Magnesium glycinate is often marketed for general supplementation, particularly when digestive comfort is a priority. While some suggest that different forms may have specific benefits for symptoms such as muscle cramps, anxiety, or sleep disturbance, it's important to note that NICE does not specifically recommend magnesium for idiopathic leg cramps, and evidence for form-specific benefits remains 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 study published in the Journal of the American College of Nutrition (Firoz & Graber, 2001) found that magnesium citrate was more bioavailable than magnesium oxide, with significantly higher serum magnesium levels following supplementation. Research on chelated magnesium forms, including glycinate, suggests potentially enhanced absorption, though the evidence base is less extensive.

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. For magnesium glycinate, it has been proposed that the chelated form may be absorbed partially intact through peptide transport pathways, potentially bypassing some of the competitive inhibition that affects free magnesium ion absorption. However, this mechanism remains theoretical and requires further research in humans.

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 well-absorbed forms. The choice between them should be guided primarily by tolerability and individual needs rather than presumed absorption differences alone.

Choosing Between Magnesium Citrate and Glycinate for Your Needs

Selecting the appropriate magnesium supplement requires consideration of individual needs, tolerability, and therapeutic goals. Both magnesium citrate and glycinate are available options, but specific circumstances 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 have experienced diarrhoea with other magnesium supplements

• You require long-term supplementation and prioritise gastrointestinal comfort

Dosing considerations: The UK Expert Group on Vitamins and Minerals (EVM) has established a guidance level of 400 mg of supplemental elemental magnesium daily for adults. The NHS notes that doses above this amount 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. 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 can reduce absorption of certain medications including:

• Tetracycline antibiotics (separate by 2-3 hours)

• Quinolone antibiotics (take magnesium at least 2 hours before or 4-6 hours after)

• Bisphosphonates (follow product-specific guidance, typically separate by at least 2 hours)

• Levothyroxine (separate by at least 4 hours)

• Iron supplements (separate by at least 2 hours)

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 <0.75 mmol/L) should be investigated for underlying causes such as malabsorption, chronic diarrhoea, or medication effects (particularly diuretics and proton pump inhibitors). According to UK clinical practice, symptomatic or severe hypomagnesaemia may require intravenous replacement under specialist supervision following local protocols.

If you experience any suspected side effects from magnesium supplements, report them to the MHRA Yellow Card Scheme (yellowcard.mhra.gov.uk).

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