Magnesium: what it does and how much you need
Magnesium helps muscles and nerves work, helps control blood sugar and blood pressure, and helps make protein, bone and DNA. Adults need 400 to 420 milligrams for men and 310 to 320 milligrams for women, from food and supplements together, and the upper limit is 350 milligrams a day from supplements (magnesium in food does not count).
General information, not medical advice. Check with a doctor or pharmacist before taking a supplement, especially if you are pregnant or breastfeeding, take any medicine, or are under 18.
In the UK
In the UK, adults need 300 milligrams a day for men and 270 milligrams for women, and the NHS says up to 400 milligrams a day from supplements is unlikely to cause harm.
How much you need and the upper limit
| US (NIH) | UK (NHS) | |
|---|---|---|
| Adults need | 400 to 420 milligrams for men and 310 to 320 milligrams for women, from food and supplements together | 300 milligrams a day for men and 270 milligrams for women |
| Upper limit | 350 milligrams a day from supplements (magnesium in food does not count) | Up to 400 milligrams a day from supplements |
The UK figure is the amount the NHS says is unlikely to cause harm. Figures are for adults.
Cautions
- Above the upper limit, magnesium supplements often cause diarrhoea and stomach cramps.
Food sources
- Beans and lentils
- Nuts and seeds
- Whole grains
- Leafy greens
- Fortified cereals
- Milk and yogurt
Forms on the label
- Magnesium glycinate is magnesium bound to the amino acid glycine, often chosen because it tends to be gentler on the stomach than magnesium oxide.
- Magnesium citrate is well absorbed, and larger amounts can loosen the stools.
- Magnesium oxide packs a lot of magnesium into each tablet but is less well absorbed than citrate or glycinate.
- Magnesium threonate is a newer form that usually carries less magnesium per capsule than other forms.
Dose questions
- Is 500 mg of magnesium too much?
- Is 400 mg of magnesium too much?
- Is 500 mg of magnesium glycinate too much?
Quick answers
- What does magnesium do?
- Magnesium helps muscles and nerves work, helps control blood sugar and blood pressure, and helps make protein, bone and DNA.
- How much magnesium do adults need?
- Adults need 400 to 420 milligrams for men and 310 to 320 milligrams for women, from food and supplements together (US, NIH). In the UK: 300 milligrams a day for men and 270 milligrams for women (NHS).
- What is the upper limit for magnesium?
- US: 350 milligrams a day from supplements (magnesium in food does not count). UK (NHS): up to 400 milligrams a day from supplements is unlikely to cause harm.
- Which foods have magnesium?
- Beans and lentils, nuts and seeds, whole grains, leafy greens, fortified cereals, milk and yogurt.
- What should I watch out for with magnesium?
- Above the upper limit, magnesium supplements often cause diarrhoea and stomach cramps.
Sources
- NIH Office of Dietary Supplements fact sheet
https://ods.od.nih.gov/factsheets/Magnesium-HealthProfessional/ - NHS vitamins and minerals guidance
https://www.nhs.uk/conditions/vitamins-and-minerals/others/
Ask Supplement Check yourself
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