Magnesium: What Is It and How Do You Choose the Right Supplement?
Written byMartin Rhodes · Last reviewed August 2026
What is magnesium?
Magnesium is a mineral that the body needs for a range of normal functions. It is found naturally in a wide variety of foods and is involved in many processes within the body.
Magnesium is sometimes confused with vitamins, but it is a mineral, not a vitamin.
The NHS explains that magnesium contributes to normal energy metabolism and is involved in the normal function of the parathyroid glands.
What does magnesium do?
Magnesium is involved in a wide range of normal processes in the body. It contributes to normal energy metabolism and has a role in normal muscle and nerve function and the maintenance of normal bones.
There are authorised nutrition and health claims for magnesium relating to several of these normal functions, but those claims can only be used for a food or supplement when the relevant conditions are met.
That's an important distinction when looking at magnesium supplements.
The fact that magnesium has a normal role in the body doesn't automatically mean that taking more magnesium will produce a particular health benefit.
How much magnesium do you need?
The amount of magnesium you need depends on factors including age and sex.
For adults aged 19 to 64, the NHS gives the following figures:
Men: 300mg per day
Women: 270mg per day
These figures relate to total magnesium intake rather than the amount you should necessarily take as a supplement.
The NHS also advises that you should be able to get all the magnesium you need by eating a varied and balanced diet.
Can you get enough magnesium from food?
Yes. Magnesium occurs naturally in a wide variety of foods.
Good sources include:
spinach and other green vegetables
nuts
wholemeal bread
wholegrain foods
seeds and other plant foods
The NHS specifically highlights spinach, nuts and wholemeal bread as sources of magnesium.
This is why we think food should always be the starting point. A supplement can be convenient, but it doesn't replace the variety of nutrients and other components provided by a balanced diet.
Do you need a magnesium supplement?
Not necessarily.
If you're eating a varied and balanced diet, you may already be getting the magnesium you need.
People choose supplements for different reasons, including convenience or because they want to increase their intake without changing their diet.
But choosing a supplement shouldn't start with the question:
“What's the strongest one I can buy?”
A better place to start is:
“What am I actually getting?”
That's where magnesium supplements can become confusing.
What does “elemental magnesium” mean?
This is one of the most useful things to understand when comparing magnesium supplements.
A supplement may be labelled with the name and weight of a magnesium compound, rather than the amount of magnesium itself.
For example, a product might contain a certain amount of magnesium glycinate, citrate or another magnesium salt. That figure isn't necessarily the same as the amount of elemental magnesium provided.
The elemental magnesium amount tells you how much magnesium itself is supplied by the compound.
So when comparing products, don't simply compare the biggest number printed on the front of the packet.
Look for the amount of elemental magnesium provided by the recommended daily serving.
That gives you a much more meaningful basis for comparing products.
Which type of magnesium is best?
This is probably one of the biggest sources of confusion when choosing a magnesium supplement.
You'll see different magnesium compounds used in supplements, including:
Magnesium glycinate or bisglycinate
Magnesium glycinate is magnesium combined with glycine. It's a commonly used form in food supplements and is often marketed as a particular type of magnesium.
Magnesium citrate
Magnesium citrate is magnesium combined with citric acid. It is also used in UK medicinal products and supplements.
Magnesium oxide
Magnesium oxide is another commonly encountered form. It contains a relatively high proportion of elemental magnesium compared with some other magnesium compounds, but the amount of a compound on the label shouldn't be confused with the amount of elemental magnesium.
Magnesium malate
Magnesium malate is magnesium combined with malic acid. You'll see it used in some supplements, although it isn't one of the magnesium salts most commonly encountered in UK clinical practice.
Magnesium L-threonate
Magnesium L-threonate is a newer form of magnesium. It was authorised as a novel food for use in food supplements in Great Britain in 2026, subject to specific conditions and labelling requirements.
If you see magnesium L-threonate on a supplement label, check that the product complies with the relevant GB requirements and follow the manufacturer's directions.
So which one is best?
There isn't a simple answer.
Different magnesium compounds have different characteristics, and the amount of magnesium actually supplied by each compound can vary.
UK Specialist Pharmacy Service guidance notes that there are no significant differences in bioavailability between several oral magnesium salts used clinically.
So be cautious about claims that one particular form is automatically “the best” or “the most absorbable”.
The right comparison starts with what the product actually contains, rather than simply the name of the magnesium compound.
Magnesium and sleep — what does the evidence say?
Search for magnesium online and you'll quickly find products marketed around sleep, relaxation and bedtime routines.
That doesn't mean magnesium should automatically be presented as a sleep supplement.
Magnesium has an important role in normal body function, but we shouldn't confuse that with evidence that taking a magnesium supplement will improve someone's sleep.
This is an area where supplement marketing can run ahead of the evidence.
The ASA has previously taken action against magnesium products where advertising made claims relating to sleep, stress, anxiety and other health effects.
So if you're considering magnesium because you're having problems with sleep, it's worth looking at the bigger picture rather than assuming a supplement is the answer.
Magnesium and muscle cramps — what does the evidence say?
Magnesium is involved in normal muscle function, which is one reason magnesium supplements are often marketed for muscle cramps.
But again, the biological role of magnesium and the effect of supplementation are not the same thing.
Evidence for magnesium supplements in treating ordinary muscle cramps is not strong enough for us to present magnesium as a treatment for cramps.
If you regularly experience unexplained or persistent muscle cramps, it's worth considering whether there may be another cause rather than automatically assuming you need more magnesium.
What does magnesium deficiency mean?
Genuine magnesium deficiency can occur, although it isn't something that should be diagnosed simply by looking at a list of everyday symptoms.
Low magnesium levels can occur in association with certain medical conditions and other factors.
The NHS notes that magnesium testing may be recommended in certain circumstances when someone has symptoms such as weakness, twitching, cramping or an irregular heartbeat.
More significant magnesium deficiency can require medical assessment and treatment.
If you're concerned that you may be deficient, particularly if you have ongoing symptoms or a medical condition, speak to a healthcare professional rather than simply increasing your supplement dose.
How much magnesium is too much?
More isn't necessarily better.
The NHS advises that taking more than 400mg of magnesium from supplements in a short period can cause diarrhoea. It also advises that excessive amounts of magnesium supplements can be harmful.
This is another reason to look at the actual elemental magnesium amount rather than simply choosing a product because the number on the front looks impressive.
If you're already getting magnesium from your diet and other supplements, remember to consider your total intake.
And always follow the directions for the particular product you're using.
Magnesium and medicines
Magnesium supplements can interact with some medicines.
For example, magnesium can affect the absorption of certain medicines, meaning that the timing of doses may need to be considered.
UK clinical guidance identifies interactions with several medicines and recommends appropriate separation of doses where necessary.
If you take regular prescription or over-the-counter medicines, speak to a pharmacist or doctor before starting a magnesium supplement.
This is particularly important if you take several medicines or have a condition affecting your kidneys.
What should I look for in a magnesium supplement?
If you're comparing magnesium supplements, don't just look at the form or the biggest number on the front.
Look at:
The form — Is it glycinate, citrate, oxide, malate or another magnesium compound?
Elemental magnesium — How much actual magnesium does the recommended daily serving provide?
Serving size — How many capsules, tablets or scoops are needed to provide that amount?
Other ingredients — What else has been added to the formulation?
Clear directions — Does the product clearly explain how much to take and how to use it?
The manufacturer — Is the company transparent about what is actually in the product?
A good supplement should make these things easy to understand.
What are we looking at for This One Is Magnesium?
We're currently researching whether magnesium is a product we'd be happy to put our name to.
We're looking at the different forms available, the amount of elemental magnesium that can realistically be provided in a convenient serving and how the finished product could fit into the This One Is range.
We haven't made a final decision on the formulation yet.
That's deliberate.
We want to understand the ingredient properly before deciding what a This One Is Magnesium product should look like.
If we do launch one, we want it to be clear about what it contains, straightforward to understand and made to a standard we'd be happy with.