What it is
Magnesium bisglycinate is magnesium bound to two molecules of glycine. It is sold as "more bioavailable" and "gentle on the stomach"; the second is plausible, but the first is not an authorised claim: the EU does not recognise that one magnesium salt is better than another.
What is authorised for magnesium, in products supplying at least 15 % of the reference amount per serving: it contributes to reducing tiredness and fatigue, to electrolyte balance, to normal muscle and nervous system function, and to the maintenance of bones and teeth. And nothing more.
What it does
Magnesium is a mineral involved in hundreds of reactions in the body:
- It takes part in muscle contraction, nerve transmission and energy metabolism.
- If the diet already provides it (pulses, nuts, wholegrain cereals), a supplement adds no benefit.
- Poorly absorbed salts (oxide, sulphate) draw water into the gut and loosen the stools; bisglycinate does so less.
At the counter
When to recommend it
- A diet low in magnesium or higher needs, with a daily supplement dose that stays within the reference amount
- Someone who tolerates other salts badly (diarrhoea with oxide or citrate) and wants to try a gentler one
- Taking medicines that lower magnesium (omeprazole and similar, diuretics) and advised by their doctor
When not to
- Kidney disease: magnesium is not eliminated well and can accumulate
- To "cure" night cramps: evidence in older people is weak and it cannot be promised
- Together with certain medicines without separating the doses (see warnings)
Warnings
- Important INTERACTIONS: magnesium reduces the absorption of bisphosphonates (alendronate), quinolones, tetracyclines and levothyroxine. Separate the doses by at least 2 hours (4 with levothyroxine).
- Important KIDNEY: in kidney failure magnesium can accumulate and cause weakness, low blood pressure or arrhythmias. Do not recommend without their doctor.
- Caution The tolerable upper intake of magnesium from supplements is 250 mg a day for adults: look at the total dose of every product.
- Worth knowing For night cramps, trials have not shown a clear benefit in older people: do not promise it.
Pharmacokinetics
- Absorption
- Variable by salt and dose: the more taken at once, the less is absorbed.
- Distribution
- Most is in bone and muscle; only a small fraction is in blood.
- Metabolism
- It is not metabolised: it is a mineral. The glycine does enter amino acid metabolism.
- Elimination
- By the kidney; in kidney failure it can accumulate.
Bisglycinate versus oxide
| Aspect | Bisglycinate | Oxide |
|---|---|---|
| Laxative effect | Lower | Higher |
| Magnesium per capsule | Less (the glycine weighs) | More (the most concentrated) |
| Price | Higher | Lower |
| What can be claimed | The same as any magnesium: nothing about "better absorption" | The same |
The difference is digestive tolerance and price, not that one salt has claims and the other does not: they are the same.
Self-assessment
Three questions. When you check your answers you will see the explanation for each one.
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Magnesium can reduce the absorption of bisphosphonates such as alendronate. Separating the doses avoids the problem.
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The EU only authorises the claims for magnesium in general; it does not distinguish between salts.
-
The kidney eliminates magnesium: if it does not work well, it builds up and can cause serious effects.
Training content. It does not replace the summary of product characteristics or clinical judgement.