# How much magnesium do you need a day? UK amounts

Source: https://magnesiumguide.uk/basics/how-much-magnesium-do-you-need/
Author: Nell Hartley · Updated 2026-11-04

**Short answer:** Adults in the UK need about 300 mg of magnesium a day for men and 270 mg for women aged 19 to 64, mostly from food. The NHS says 400 mg a day or less from supplements is unlikely to cause harm. Food magnesium doesn't count towards that limit, because the kidneys clear any excess from food easily.

## How much do UK adults need?

The UK government's dietary recommendations, which the NHS uses, are:

| Age | Males | Females |
| --- | --- | --- |
| 1 to 3 years | 85 mg | 85 mg |
| 4 to 6 years | 120 mg | 120 mg |
| 7 to 10 years | 200 mg | 200 mg |
| 11 to 14 years | 280 mg | 280 mg |
| 15 to 18 years | 300 mg | 300 mg |
| 19 and over | 300 mg | 270 mg |

These are reference nutrient intakes: enough for almost everyone in the group, so many people need less. The adult figures stay the same after 65.

## How do other countries compare?

| Body | Men | Women |
| --- | --- | --- |
| UK (NHS) | 300 mg | 270 mg |
| European Food Safety Authority | 350 mg | 300 mg |
| United States (adults 31 and over) | 420 mg | 320 mg |

The US figures are higher because its committee used different studies of how much the body needs to stay in balance. None of these is "right"; together they suggest most adults need roughly 270 to 420 mg a day.

## Do you need more in pregnancy, breastfeeding or sport?

The UK sets no extra amount for pregnancy, because the body absorbs and holds on to more. While breastfeeding, the UK reference intake rises by 50 mg a day. Athletes lose some magnesium in sweat, but a diet that matches their higher energy intake usually covers it. Older adults absorb less and lose more through the kidneys, which is one reason they are more likely to [run short](/basics/deficiency-symptoms/).

## How much is too much?

From **food**, there is no practical upper limit for healthy people: the kidneys get rid of any excess.

From **supplements**, the limits are about the gut, not poisoning:

- The NHS says 400 mg a day or less from supplements is unlikely to cause any harm, and that higher doses can cause diarrhoea.
- The European upper level for supplemental magnesium is 250 mg a day, set to avoid mild diarrhoea in a small share of people.
- The US upper limit for supplements is 350 mg a day for adults.

Higher doses are sometimes used for specific reasons, such as about 600 mg a day for [migraine prevention](/benefits/migraine/) or as a [laxative](/benefits/constipation/), but those are best agreed with a GP or pharmacist. Anyone with kidney disease should take magnesium supplements only on medical advice, because the kidneys may not clear the excess.

## Does the number on the label mean the same thing?

Not always. These amounts refer to **elemental magnesium**, the magnesium itself. A capsule containing 500 mg of magnesium glycinate holds only about 70 mg of magnesium. UK labels must state the elemental amount, but some print the compound weight more prominently. Our [forms guide](/forms/) and [cost calculator](/buying-guide/) show how to convert.

## How do you know if you're getting enough?

Roughly: a day with wholegrain bread or porridge, a handful of nuts or seeds, beans or lentils and some green vegetables will get most adults to their reference intake. See [foods high in magnesium](/basics/food-sources/).

## Frequently asked questions

### Is 400 mg of magnesium a day too much?

Not for most healthy adults. The NHS says up to 400 mg a day from supplements is unlikely to cause harm. Higher doses can cause diarrhoea, and people with kidney disease should only take magnesium supplements on medical advice.

### Do children need magnesium supplements?

Rarely. Children need 85 mg a day at age 1 to 3, rising to 300 mg by 15 to 18, and a normal diet usually provides it. Don't give children adult magnesium supplements without advice from a GP or pharmacist.

### Why are US magnesium amounts higher?

Different expert committees weigh the evidence differently. The US sets 400 to 420 mg a day for men and 310 to 320 mg for women. All of them agree on the broad range: roughly 250 to 420 mg a day for adults.

### How much magnesium do you need when breastfeeding?

The UK reference intake goes up by 50 mg a day while breastfeeding, to about 320 mg for most women. Pregnancy has no extra amount. Food is the best source; ask your midwife or GP before taking a supplement.

## References

1. [Public Health England. Government dietary recommendations, 2016.](https://assets.publishing.service.gov.uk/media/5a749fece5274a44083b82d8/government_dietary_recommendations.pdf)
2. [NHS. Vitamins and minerals: others (magnesium).](https://www.nhs.uk/conditions/vitamins-and-minerals/others/)
3. [EFSA Panel on Dietetic Products, Nutrition and Allergies. Scientific opinion on dietary reference values for magnesium. EFSA Journal, 2015.](https://www.efsa.europa.eu/en/efsajournal/pub/4186)
4. [National Institutes of Health Office of Dietary Supplements. Magnesium: fact sheet for health professionals.](https://ods.od.nih.gov/factsheets/Magnesium-HealthProfessional/)