Magnesium glycinate, also sold as magnesium bisglycinate, is one of the most popular supplements of the moment, often promoted for sleep, stress and cramps. It is simply magnesium bound to glycine, an amino acid. That form has a real practical advantage, as it tends to be easier on the stomach than some others. The bigger promises are much less proven, and most people who eat a varied diet get enough magnesium without any supplement.
In short
| What to know | The benchmark |
|---|---|
| What it is | Magnesium bound to glycine, an amino acid; “bisglycinate” means two glycine molecules per magnesium |
| Main practical advantage | Usually gentler on the gut than magnesium oxide or citrate, which have a stronger laxative effect |
| Daily need from food | 300 mg a day for men and 270 mg for women aged 19 to 64 (NHS) |
| Supplement limit | The NHS says 400 mg or less a day from supplements is unlikely to cause harm; EFSA sets 250 mg a day for supplemental magnesium |
| Well established | Magnesium is needed for muscles, nerves, energy and bones |
| Not well established | Better sleep, less anxiety or fewer cramps in people who are not deficient |
What magnesium glycinate is
Magnesium supplements are never pure magnesium: the mineral is always bound to another compound, which gives the “form”. Common ones include oxide, citrate, chloride, malate and glycinate.
In this form, the mineral is attached to glycine. Glycine is heavier than magnesium, so a large part of the weight of the powder is glycine. That is why the figure that matters on the label is the amount of elemental magnesium per dose, not the amount of “magnesium glycinate”. A capsule labelled with a large number of milligrams of magnesium glycinate may contain much less actual magnesium.
How it compares with other forms
- Magnesium oxide is cheap and contains a lot of magnesium per gram, but it is less well absorbed and more likely to cause loose stools. It is often used as a laxative or for indigestion.
- Magnesium citrate is well absorbed and also has a noticeable laxative effect, which some people want and others do not.
- Glycinate is generally described as well absorbed and less likely to upset the stomach, which makes it a common choice for people who had diarrhoea with other forms.
Manufacturers often claim that glycinate is “far better absorbed” than every other form. Studies comparing forms head to head in people are small and use different methods, so these claims go beyond what has been shown. What counts most is getting the right amount of elemental magnesium in a form you tolerate.
What magnesium does in the body
Magnesium helps turn food into energy, keeps muscles and nerves working normally, and contributes to healthy bones and teeth. In the UK, the authorised health claims for magnesium include that it contributes to the reduction of tiredness and fatigue, to normal muscle function and to normal psychological function.
These claims describe what magnesium does when you get enough of it. They do not mean that taking more than you need gives more energy or better muscles.
What the evidence says on common claims
Sleep
This form is widely marketed for sleep. Research on magnesium and sleep is limited: trials are small, often in older adults, and the results are mixed. There is no strong evidence that a supplement improves sleep in someone who is not short of magnesium.
Stress and anxiety
Magnesium plays a role in the nervous system, which is why it is linked to stress. Studies on anxiety are few and of modest quality, and they do not allow firm conclusions.
Cramps
Leg cramps are one of the most common reasons people buy magnesium. A Cochrane review concluded that magnesium supplements are unlikely to give a meaningful benefit for the usual night cramps of older adults.
How much magnesium you need
According to the NHS, adults aged 19 to 64 need:
- 300 mg a day for men;
- 270 mg a day for women.
You should be able to get this from a varied diet. Good sources include green leafy vegetables such as spinach, nuts, seeds, wholemeal bread and brown rice, and pulses such as beans and lentils.
If you take a supplement
- Check the elemental magnesium on the label and add up any magnesium in multivitamins or other products you take.
- Stay within safe amounts: the NHS says having 400 mg or less a day from supplements is unlikely to cause harm, while taking high doses for a short time can cause diarrhoea. The European Food Safety Authority sets a lower upper level of 250 mg a day for supplemental magnesium, based on the risk of diarrhoea.
- Take it with food if it upsets your stomach.
Some situations call for advice before starting:
- kidney disease, because the kidneys may not clear excess magnesium;
- medicines that magnesium can make less effective if taken at the same time, such as some antibiotics (tetracyclines, quinolones), levothyroxine for the thyroid and bisphosphonates for osteoporosis: ask your pharmacist how many hours to leave between them;
- pregnancy and breastfeeding.
If tiredness is what makes you think of magnesium, keep in mind that it often has other causes, such as iron deficiency or vitamin D deficiency. More on vitamins and minerals in our Nutrition section.
When to see a GP
Book an appointment if you have:
- tiredness, poor sleep or low mood lasting several weeks;
- frequent muscle cramps, twitches or tremors that do not settle;
- long-lasting diarrhoea, a bowel condition, type 2 diabetes, or you take a stomach acid medicine or a diuretic long term, all of which can lower magnesium levels;
- kidney disease or a long-term treatment, and you want to take a magnesium supplement.
Call 999 if you have chest pain, a very irregular or pounding heartbeat with dizziness, or you faint.
