How Much Magnesium Per Day? UK Amounts by Age and Sex

UK adults need 300 mg of magnesium a day for men and 270 mg for women, and children need 85 to 300 mg a day depending on age; those are the government reference intakes for everything eaten and drunk in a day, not supplement doses.^{1, 2} Other figures are different kinds of number: 375 mg is the reference value a label's percentage is worked out from, the NHS says 400 mg or less a day from supplements is unlikely to cause harm, and Europe's upper level for supplemental magnesium is 250 mg.^{1, 3, 4} It sits inside the Wellgard vitamins and minerals guide.

How much magnesium do adults need a day in the UK?

The NHS page on vitamins and minerals, last reviewed 3 August 2020, gives "300mg a day for men (19 to 64 years)" and "270mg a day for women (19 to 64 years)".¹ Those are the UK reference nutrient intakes, set in 1991 and republished by Public Health England in 2016, and they do not fall after 64: the government table repeats them at 65 to 74 and at 75 and over.² The intake is the amount judged enough for nearly everyone, from the whole day's food; the NHS says you should be able to "get all the magnesium you need by eating a varied and balanced diet", naming spinach, nuts and wholemeal bread.¹

How much magnesium do children and teenagers need?

The children's figures come from the same 1991 values, published by Public Health England in 2016; they are the same for boys and girls and describe the day's food, not a supplement dose.²

No UK body recommends a magnesium supplement for children. The NHS page on vitamins for children, reviewed 30 May 2024, recommends for children aged 6 months to 5 years "vitamin supplements containing vitamins A, C and D", does not mention magnesium, and says "talk to a pharmacist about which supplement would be most suitable for your child".⁵ A magnesium supplement for a child under 12 is a GP or pharmacist question. The vitamin D version of this section is on how much vitamin D babies and children need.

What do the 375 mg, 400 mg, 250 mg and 350 mg figures each mean?

Three committees read much the same trials and chose 250, 350 and 400 mg because mild diarrhoea was the only effect any found above those amounts; the UK group found "insufficient data to establish a Safe Upper Level".^{4, 6, 7}

Is 500 mg of magnesium too much?

500 mg a day of magnesium is above all three supplement limits. The NHS says "Taking high doses of magnesium (more than 400mg) for a short time can cause diarrhoea".¹ Trials have used 500 mg and more under supervision: 46 older adults with insomnia took 500 mg a day for eight weeks, and a 2023 review found seven studies at 128 to 1,200 mg a day with no more diarrhoea than placebo.^{7, 9} None sets a dose for anyone reading this, and trials of magnesium oxide often quote the compound: 500 mg of magnesium oxide is about 300 mg of magnesium. What loose stools look like by dose is on magnesium side effects.

How much magnesium is in a supplement? Elemental versus compound

Elemental magnesium is the magnesium itself. In a supplement it is bound to a partner, and the compound weighs far more than the mineral in it. Calculated from the formulas, magnesium oxide is about 60% magnesium by weight, malate about 15.5%, bisglycinate about 14%, citrate 11 to 16% depending on the hydrate, citrate malate 12 to 15%, and L-threonate about 8%.⁸ So 500 mg of bisglycinate carries about 70 mg of magnesium, 500 mg of citrate about 55 to 80 mg, and 500 mg of oxide about 300 mg. These are calculations; the nutrition panel's magnesium line, required by law in milligrams and as a percentage of 375 mg, is the number to set against every figure here.³ More on how to choose a magnesium supplement and what magnesium glycinate is.

How much magnesium do women need, and does pregnancy change it?

270 mg a day from 19 onwards, and the published UK tables carry no extra amount for pregnancy.² The European 250 mg supplemental level was written with pregnancy in mind: it "holds for adults, including pregnant and lactating women".⁴ Until the pregnancy page is written, ask your midwife or GP before adding any supplement in pregnancy, and treat nothing here as a pregnancy dose.

How much magnesium do men and older adults need?

300 mg a day at every age from 19; the 65 to 74 and 75-plus rows of the government table repeat the 19 to 64 figures.² One small study is often quoted: a four-week trial in taekwondo athletes and sedentary men given 10 mg of magnesium per kilogram of body weight a day reported higher free and total testosterone, with larger rises in the athletes; it changes no reference intake.¹⁰ What changes with age is not the target but the odds of falling short, because several medicines common after 60 lower magnesium, among them proton pump inhibitors, diuretics, some antibiotics and some cancer drugs; anyone on one of these should keep a supplement within the 400 mg guidance level and mention it at their medication review.¹¹ The foods that close a gap are on what foods contain magnesium.

Who gets too much, and who gets too little?

In healthy people the kidney "reabsorbs 95% of the filtered load of magnesium" and passes the rest in urine.⁶ Serious excess, hypermagnesaemia, is "relatively uncommon but potentially life-threatening" and is seen mainly in "patients with impaired renal function or those receiving magnesium-containing medications or supplements".¹² With kidney disease, take no magnesium supplement, antacid or laxative without your kidney team's agreement. Too little is more ordinary: a diet short of wholegrains, nuts and green vegetables, or one of the medicines above.¹¹ The everyday limits are on is it OK to take magnesium every day, the medicines on what you should not take with magnesium, and the zinc figures on how much zinc per day.

What we don't know

Whether any official body will revisit its limit: the 2023 call to re-evaluate the American figure came from a magnesium research centre, and nothing has changed.⁷ What long-term high doses do; the NHS says there is not enough evidence.¹ And the amounts for babies under 1 and during breastfeeding, which sit in the 1991 report, not the 2016 table.

Frequently asked questions

How much magnesium per day for a woman?

270 mg a day at every age from 19, with no pregnancy increment in the published tables.² Magnesium contributes to the maintenance of normal bones, and the intake is met from food at 60 as at 30, with a supplement where the diet falls short.

How much magnesium per day for a man?

300 mg a day at every age from 19, from the whole day's food.^{1, 2}

How much magnesium is too much?

For supplements, 400 mg a day is the UK guidance level and 250 mg the European upper level; the NHS says more than 400 mg for a short time can cause diarrhoea.^{1, 4, 6} Dangerous excess is rare and almost always involves kidney disease; what the trials recorded is on magnesium side effects.

How much magnesium should a teenager have?

280 mg a day at 11 to 14 and 300 mg at 15 to 18, from meals.² If a supplement is wanted, a pharmacist or GP should agree the elemental amount.

Is 375 mg of magnesium the recommended dose?

No. 375 mg is the nutrient reference value labels use for the percentage figure, set in Regulation 1169/2011; it is not the UK intake and not a dose. A supplement showing 100% of it gives 375 mg, above the European 250 mg level and below the UK 400 mg guidance level.^{3, 4, 6}

Sources

1. NHS. Vitamins and minerals: others, magnesium section. Page last reviewed 3 August 2020; next review was due 3 August 2023. nhs.uk.
2. Public Health England. Government Dietary Recommendations, Tables 5 and 6. August 2016. gov.uk.
3. Retained Regulation (EU) No 1169/2011, Annex XIII: nutrient reference values and significant amounts. legislation.gov.uk.
4. Scientific Committee on Food. Opinion on the Tolerable Upper Intake Level of Magnesium, 2001, in EFSA, Tolerable Upper Intake Levels for Vitamins and Minerals, 2006. efsa.europa.eu.
5. NHS. Vitamins for children. Page last reviewed 30 May 2024. nhs.uk.
6. Expert Group on Vitamins and Minerals. Safe Upper Levels for Vitamins and Minerals, 2003, magnesium risk assessment. UK Government Web Archive.
7. Costello R, et al. Perspective: Call for Re-evaluation of the Tolerable Upper Intake Level for Magnesium Supplementation in Adults. Advances in Nutrition, 2023. PubMed 37487817.
8. EFSA Panel on Nutrition, Novel Foods and Food Allergens. Magnesium citrate malate as a source of magnesium added for nutritional purposes to food supplements. EFSA Journal, 2018. PubMed 32625777.
9. Abbasi B, et al. The effect of magnesium supplementation on primary insomnia in elderly: a double-blind placebo-controlled clinical trial. Journal of Research in Medical Sciences, 2012. PubMed 23853635.
10. Cinar V, et al. Effects of magnesium supplementation on testosterone levels of athletes and sedentary subjects at rest and after exhaustion. Biological Trace Element Research, 2011. PubMed 20352370.
11. Liamis G, et al. An overview of diagnosis and management of drug-induced hypomagnesemia. Pharmacology Research and Perspectives, 2021. PubMed 34278747.
12. Aal-Hamad AH, et al. Hypermagnesemia in clinical practice. Medicina, 2023. PubMed 37512002.

This article is general information, not medical advice.