'1,040 mg magnesium' is really 208 mg: how to read the label
Magnesium supplements often show two numbers. Here's the one that matters, how much you need, and what magnesium can honestly claim to do.
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Pick up a magnesium supplement and you might see something like "208 mg elemental from 1,040 mg". Which number is the dose you're actually getting?
The number that matters: elemental magnesium
Magnesium in supplements is always bound to another substance, such as glycine, citrate or oxide. The big number (here 1,040 mg) is the weight of the whole compound. The smaller number (208 mg) is the elemental magnesium, the amount of magnesium itself.
The elemental number is your dose. The bigger number can make a product look stronger than its competitors when it isn't.
If a label only shows the compound weight, check the nutrition table on the back. It should list magnesium in mg and as a percentage of the NRV (nutrient reference value, 375 mg for adults on UK and EU labels).
How much do you need?
- UK/EU labelling reference: 375 mg a day (the NRV).
- US recommended amounts (NIH): 310–320 mg a day for adult women and 400–420 mg for adult men, from food and supplements combined.
- US upper limit for supplements: 350 mg a day of magnesium from supplements for adults. Higher amounts can cause diarrhoea, nausea and cramps.
Many people get a good share from food: nuts, seeds, whole grains, beans and leafy greens.
What magnesium can honestly claim
Under UK rules, supplements can only use approved health claims. For magnesium, these include that it contributes to:
- a reduction of tiredness and fatigue
- normal functioning of the nervous system
- normal muscle function
- normal psychological function
- the maintenance of normal bones and teeth
"Helps you sleep", "calms anxiety" and "eases menopause symptoms" are not approved claims. If a product says them, treat that as a warning sign about the brand.
Our picks
Best for: People who want a gentle form
Magnesium glycinate (bisglycinate) capsules, clearly labelled with elemental magnesium
Glycinate is a popular form that many people find gentle on the stomach. Choose a brand that states the elemental magnesium per serving clearly on the front or in the nutrition table.
Worth knowing: Check the total elemental dose per serving. Doubling up capsules can put you above the US upper limit for supplemental magnesium (350 mg a day).
See options on Amazon (affiliate link, opens in new tab)Best for: A widely available, lower-cost option
Magnesium citrate tablets
A common, well-absorbed form, often cheaper than glycinate.
Worth knowing: Citrate is more likely to have a laxative effect at higher doses.
See options on Amazon (affiliate link, opens in new tab)The short version
- Look for elemental magnesium per serving and ignore the compound weight.
- Most adults don't need more than about 350 mg a day from supplements.
- Be sceptical of sleep and anxiety promises. They're not approved claims.
- Check with a pharmacist if you take other medicines or have kidney problems.
Common questions
Does magnesium help you sleep?
It's a popular claim, but 'helps sleep' isn't an approved health claim for magnesium in the UK or EU, and the research in healthy adults is limited and mixed. Approved claims include that it contributes to a reduction of tiredness and fatigue and to normal psychological function.
Which form of magnesium is best?
Forms differ in how much magnesium they contain and how they're tolerated. Glycinate and citrate are popular and generally well absorbed; oxide contains a lot of magnesium by weight but is less well absorbed. The elemental dose matters more than the form name.
Who should avoid magnesium supplements?
Speak to a doctor first if you have kidney disease, or if you take medicines such as some antibiotics, osteoporosis medicines (bisphosphonates) or diuretics, because magnesium can interact with them.
Sources we checked
- Magnesium: fact sheet for health professionals (US National Institutes of Health, Office of Dietary Supplements)
- Great Britain nutrition and health claims (NHC) register (UK Government)
This article is general information, not medical advice. Speak to a doctor, pharmacist or other qualified clinician about your own health, especially before starting a supplement or if symptoms are new, severe or worrying.
Got a question about this, or a claim you want checked? Ask us.
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