Magnesium bisglycinate and magnesium glycinate are chelated forms of magnesium supplements commonly available in the UK. Many people wonder whether these two terms represent different products or if they are essentially the same. In practical terms, magnesium bisglycinate and magnesium glycinate are often used interchangeably by manufacturers, with both referring to magnesium bound to the amino acid glycine. Understanding the relationship between these forms can help you make informed decisions about supplementation. This article examines the similarities and differences between magnesium bisglycinate and magnesium glycinate, their absorption profiles, and guidance on selecting the most appropriate form for your needs.

What Are Magnesium Bisglycinate and Magnesium Glycinate?

Magnesium bisglycinate and magnesium glycinate are chelated forms of magnesium supplements that are widely available in the UK. Understanding the relationship between these two terms is essential for making informed choices about supplementation.

Magnesium glycinate technically refers to magnesium bound to glycine. However, it's important to note that many products marketed as 'magnesium glycinate' are actually magnesium bisglycinate chelates, and pure monoglycinate forms are uncommon in supplements.

Magnesium bisglycinate (also known as magnesium diglycinate) describes magnesium bound to two molecules of glycine. The prefix 'bis-' indicates this double binding. In practical terms, magnesium bisglycinate and magnesium glycinate are often used interchangeably in supplement labelling, and there is considerable debate within the pharmaceutical industry about whether they represent meaningfully different compounds. Some manufacturers use the terms synonymously, whilst others distinguish between them based on the precise molecular structure.

From a clinical perspective, both forms may offer similar benefits: they are chelated to glycine, which may enhance tolerability and reduce the gastrointestinal side effects commonly associated with some other magnesium salts. The glycine component itself may theoretically provide additional effects, as glycine functions as an inhibitory neurotransmitter in the central nervous system, though evidence for additional clinical benefits at typical supplement doses is limited. When selecting supplements in the UK, patients should focus on the elemental magnesium content and product quality rather than becoming overly concerned about the glycinate versus bisglycinate distinction, as there is limited evidence for significant clinical differences between these specific forms.

Absorption and Bioavailability Comparison

The bioavailability of magnesium supplements varies depending on the chemical form, with some evidence suggesting that organic forms such as magnesium glycinate and bisglycinate may have different absorption profiles compared to inorganic salts.

Mechanism of absorption: Chelated magnesium compounds may be absorbed through different pathways in the small intestine. The amino acid chelate might protect the magnesium from forming insoluble complexes with substances in the diet such as phytates or oxalates, which can impair absorption. Some research suggests that magnesium-amino acid complexes might utilise different intestinal transport mechanisms than non-chelated forms, though direct evidence in humans is limited.

Research comparing various magnesium forms has shown mixed results, but several studies suggest that organic forms, including glycinate forms, may achieve better absorption than magnesium oxide. However, it is important to note that there is no robust clinical evidence demonstrating a significant difference in bioavailability between magnesium glycinate and magnesium bisglycinate specifically.

Gastrointestinal tolerability is another important aspect when considering magnesium supplements. Some magnesium forms, particularly at higher doses, can cause osmotic diarrhoea because unabsorbed magnesium draws water into the intestinal lumen. Chelated forms like magnesium glycinate and bisglycinate are often better tolerated by many people, though individual responses vary. Magnesium citrate, while relatively well absorbed, is more likely to have a laxative effect at higher doses. The potentially improved tolerability of glycinate forms means some patients may find it easier to maintain consistent supplementation, though it's advisable to start with lower doses and increase gradually if needed.

Which Form of Magnesium Should You Choose?

Selecting the appropriate magnesium supplement depends on individual health needs, tolerability, and specific therapeutic goals. For many people in the UK seeking general magnesium supplementation, either magnesium glycinate or bisglycinate may be a suitable choice due to their potential for good absorption and tolerability.

Clinical considerations for glycinate forms include:

• Magnesium deficiency correction: When laboratory testing or clinical assessment indicates low magnesium status, well-absorbed forms may help restore body stores

• Sleep and relaxation: While some preliminary evidence suggests magnesium may support sleep quality and nervous system function, these effects are not specific to glycinate forms and research remains limited

• Individuals with gastrointestinal sensitivity: Those who have experienced digestive discomfort with other magnesium forms may wish to try glycinate preparations

• Long-term supplementation: The potentially reduced gastrointestinal effects may make these forms suitable for sustained use

Practical considerations when choosing between products labelled as glycinate versus bisglycinate are minimal. Patients should instead focus on:

• Elemental magnesium content: Check the label for the amount of elemental magnesium per dose, not just the total compound weight

• Product quality: Select supplements from reputable manufacturers that adhere to Good Manufacturing Practice (GMP) standards

• Independent quality testing: Products that undergo independent quality testing may provide additional assurance

• Cost-effectiveness: Prices vary considerably; compare based on elemental magnesium content per dose

It is worth noting that other magnesium forms may be preferable for specific purposes. For example, magnesium citrate is sometimes used for constipation relief due to its laxative effect. Patients with complex medical conditions or those taking multiple medications should consult their GP or a registered dietitian before starting supplementation, as magnesium can interact with certain medications including antibiotics (tetracyclines, quinolones), bisphosphonates (separate by at least 30 minutes after alendronate), levothyroxine (separate by at least 4 hours), and iron supplements (separate by at least 4 hours).

Dosage and Safety Considerations in the UK

The UK's Department of Health and Social Care has established guidance on safe magnesium intake levels, which healthcare professionals and patients should follow when considering supplementation.

Reference Nutrient Intake (RNI) for magnesium in the UK is:

• Men: 300 mg per day

• Women: 270 mg per day

• For pregnancy, the RNI remains the same as for non-pregnant women

• During lactation, there may be a slightly increased requirement

The safe upper level for magnesium from supplements (not including dietary sources) is set at 400 mg per day for adults by the UK Expert Group on Vitamins and Minerals. This limit specifically applies to supplemental magnesium, as excessive intake can cause adverse effects including diarrhoea, nausea, and abdominal cramping. Whilst magnesium glycinate and bisglycinate may be better tolerated than some other forms, exceeding recommended doses is not advisable.

Dosing recommendations for magnesium glycinate or bisglycinate typically range from 200–400 mg of elemental magnesium daily, often divided into two doses to optimise absorption. Patients should carefully read supplement labels, as products list varying amounts of the magnesium compound versus elemental magnesium content.

Safety considerations and contraindications:

• Renal impairment: Individuals with chronic kidney disease should avoid magnesium supplementation unless specifically advised by their nephrologist, as impaired renal excretion can lead to dangerous hypermagnesaemia

• Medication interactions: Magnesium can reduce absorption of certain medications; separate from tetracyclines and quinolones by 2-3 hours, from bisphosphonates according to specific product guidance, and from levothyroxine and iron by at least 4 hours

• High doses: Patients should be cautious with high doses, particularly if taking medications that affect magnesium levels or in those with impaired kidney function

When to seek medical advice: Patients should contact their GP if they experience persistent symptoms potentially related to magnesium deficiency (muscle cramps, fatigue, irregular heartbeat) or if they develop signs of excessive intake (severe diarrhoea, muscle weakness, confusion, breathing difficulties). Suspected adverse reactions to supplements can be reported through the MHRA Yellow Card scheme (yellowcard.mhra.gov.uk or the Yellow Card app).

Routine magnesium supplementation should not replace a balanced diet rich in magnesium-containing foods such as green leafy vegetables, nuts, seeds, and whole grains. In the UK, magnesium supplements are regulated as foods under the Food Supplements Regulations 2003 and overseen by the Office for Product Safety and Standards (OPSS) and the Food Standards Agency (FSA), unless medicinal claims are made, in which case MHRA regulations would apply.

Frequently Asked Questions