Magnesium bisglycinate and magnesium glycinate are chelated forms of magnesium supplements commonly available in the UK. Many people encounter both terms when selecting supplements and wonder whether there is a meaningful difference between them. In practice, these terms are often used interchangeably on product labels, as most supplements labelled 'magnesium glycinate' actually contain the bisglycinate form, where magnesium is bound to two glycine molecules. Understanding this relationship helps clarify supplement choices. Both forms are valued for their potential tolerability and absorption characteristics compared to some other magnesium salts, making them popular options for addressing magnesium deficiency or supporting general wellbeing.

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 important for making informed choices about supplementation.

Magnesium bisglycinate (also known as magnesium diglycinate) describes magnesium bound to two molecules of glycine. The prefix 'bis-' indicates this double binding. This creates a stable compound that is generally well-tolerated by the digestive system.

Magnesium glycinate is a term that, in practice, is often used interchangeably with magnesium bisglycinate on supplement labels in the UK. While technically 'glycinate' could refer to a single glycine molecule bound to magnesium, most supplements labelled as 'magnesium glycinate' are actually referring to the bisglycinate chelate.

In practical terms, these terms are frequently used synonymously in supplement labelling. The chelation process involves forming a protective structure around the magnesium ion, which may help prevent it from interacting with other compounds in the gastrointestinal tract that could potentially limit absorption.

Both forms may offer similar benefits in terms of tolerability compared to some other magnesium salts. Glycine itself functions as an inhibitory neurotransmitter in the central nervous system, though whether the glycine component in these supplements provides additional benefits at typical doses remains theoretical.

When selecting supplements in the UK, it's advisable to focus on the elemental magnesium content and product quality rather than becoming overly concerned about the glycinate versus bisglycinate terminology, as the practical differences between products with these labels are typically minimal.

Absorption and Bioavailability Comparison

The bioavailability of magnesium supplements varies depending on the chemical form, with different magnesium compounds showing different absorption profiles.

Mechanism of absorption: Chelated magnesium compounds like glycinate/bisglycinate may be absorbed differently than some inorganic magnesium salts. The amino acid chelate might help protect the magnesium from forming insoluble complexes with substances in the diet such as phytates or oxalates, which could potentially impair absorption. However, it's worth noting that the precise mechanisms of absorption for different magnesium forms in humans are not fully established, and chelates may partially dissociate prior to absorption.

Research comparing various magnesium forms has suggested that organic forms, including glycinate forms, may achieve better absorption than some inorganic salts like magnesium oxide. However, absorption rates vary considerably between individuals and studies. It's important to note that there is no robust clinical evidence demonstrating a significant difference in bioavailability between products labelled as magnesium glycinate versus magnesium bisglycinate specifically.

Gastrointestinal tolerability is another important aspect when considering magnesium supplements. Magnesium oxide often causes osmotic effects because a significant portion remains unabsorbed and draws water into the intestinal lumen. Magnesium citrate, while generally better absorbed than oxide, may still have a laxative effect at higher doses. In comparison, the chelated glycinate forms may be better tolerated by some individuals, particularly at higher doses, making them potentially suitable for those with sensitive digestive systems. This improved tolerability means some people may find it easier to maintain consistent supplementation without experiencing dose-limiting side effects that can compromise adherence.

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 good choice due to their potential for good absorption and tolerability.

Potential uses for glycinate forms include:

• Magnesium deficiency correction: When laboratory testing or clinical assessment indicates low magnesium status

• Sleep and relaxation support: Some preliminary evidence suggests potential benefits, though research specifically on glycinate forms for these purposes is limited

• Individuals with gastrointestinal sensitivity: Those who have experienced digestive discomfort with other magnesium forms may find these forms better tolerated

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

Practical considerations when choosing between products labelled as glycinate versus bisglycinate are minimal. 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

• Third-party testing: Products certified by independent organisations provide additional assurance

• Cost-effectiveness: Compare prices 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 commonly 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, bisphosphonates, levothyroxine (separate by at least 4 hours), oral iron preparations, and some diuretics.

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 should be followed when considering supplementation.

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

• Men: 300 mg per day

• Women: 270 mg per day

• The RNI is not routinely increased during pregnancy or lactation

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. Carefully read supplement labels, as products list varying amounts of the magnesium compound versus elemental magnesium content. For example, 2000 mg of magnesium bisglycinate may contain only 200 mg of elemental magnesium.

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 (signs include flushing, hypotension, confusion)

• Medication interactions: Magnesium can reduce absorption of certain medications:

• Levothyroxine: separate by at least 4 hours
• Antibiotics (tetracyclines, quinolones): separate by 2-4 hours
• Bisphosphonates: separate by at least 2 hours

• Oral iron: take at different times of day

• Cardiac medications: Patients taking digoxin should consult their GP before supplementing

When to seek medical advice: Contact your GP if you experience persistent symptoms potentially related to magnesium deficiency (muscle cramps, fatigue, irregular heartbeat) or if you develop signs of excessive intake (severe diarrhoea, muscle weakness, breathing difficulties). 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 food supplements under food law, not as medicines. If you experience any suspected side effects from taking magnesium supplements, you can report them through the MHRA Yellow Card scheme.

Frequently Asked Questions