Can you have too much magnesium? Daily amounts, upper limits and what the research says

This is a general, sourced guide, not medical advice. If you have a long-term condition, are expecting a baby, or take regular medicines, talk to your doctor or pharmacist before taking magnesium.

How much magnesium do adults need each day?

Most authorities land between 270 and 420 mg a day for adults, from food. Men need more than women, and the amount rises slightly after 30 in the systems that follow the US model.

Australia and New Zealand share one set of Nutrient Reference Values from the NHMRC, which recommends 400 mg a day for men aged 19–30 and 420 mg from 31, and 310 mg for women aged 19–30 and 320 mg from 31 (NHMRC). The US uses the same figures, set by the Institute of Medicine (now the National Academies) in 1997 and summarised by the NIH Office of Dietary Supplements (NIH ODS). Canada uses the same Dietary Reference Intakes, developed jointly with the US (Government of Canada).

The UK sets lower figures: 300 mg a day for men and 270 mg for women aged 19–64 (NHS). These are the Reference Nutrient Intakes from the UK government's 1991 COMA report.

What are the amounts for children and teens?

Needs climb steeply through childhood and peak in the teenage years. In Australia, NZ, the US and Canada the figures are identical.

Sources: NHMRC, NIH ODS. Infant figures, and the slightly different figures for people expecting or breastfeeding a baby, are on the NHMRC and NIH pages; ask your GP or midwife.

Notice that the supplement limit for teens and adults (350 mg) is lower than the daily intake for most adults. That isn't a contradiction. The intake figure is for magnesium from all sources, mainly food. The upper limit counts only magnesium from supplements and medicines, on top of food.

How do the six countries compare?

The numbers differ more than you'd expect, mostly because each body read the same research with a different method.

Sources: NHMRC, NIH ODS, Government of Canada, NHS, EVM 2003, SA labelling regulations R146, EFSA 2015, EFSA ULs.

### Why do the countries differ?

Three reasons stand out.

• Different methods. The US/Canada and AU/NZ figures are RDAs or RDIs, built from balance studies to cover nearly everyone (97–98%). The UK's 1991 RNIs came from older, smaller data. The EU's EFSA gave up on a precise requirement and set an Adequate Intake based on what European adults typically eat (EFSA 2015).
• Different endpoints for the limit. Every limit here is based on the same mild effect, diarrhoea from supplements, but the bodies picked different "safe" doses from the trials. The US and AU/NZ chose 350 mg. EFSA's Scientific Committee chose 250 mg, the lowest dose at which it judged no laxative effect was seen (EFSA ULs). The UK Expert Group on Vitamins and Minerals set a 400 mg guidance level, which is advice rather than a formal limit (EVM 2003).
• Different purposes. South Africa's figure is a labelling reference value used to calculate "% NRV" on food packs, not an age-by-age recommendation.

What does South Africa recommend?

We couldn't find a separate South African recommended intake table for magnesium. What exists in law is a food-labelling Nutrient Reference Value of 310 mg a day for everyone aged 37 months and older, set in the Foodstuffs, Cosmetics and Disinfectants Act labelling regulations (R146) (SA labelling regulations R146). The regulations say the NRVs are based on RDAs. In practice, the US/Canadian age-by-age figures above are the most useful guide, and a South African dietitian can tell you what applies to you.

Can you get too much magnesium from food?

Not if your kidneys work normally. The NIH says magnesium from food poses no risk for people with normal kidney function because the kidneys remove the excess in urine, which is why the upper limit excludes food (NIH ODS). Good food sources include leafy greens, nuts, seeds, legumes and wholegrains. In Australia, tap and bottled water and coffee also make a real contribution (ABS).

What about supplements, electrolyte drinks and sprays or baths?

Supplements and electrolyte drinks are swallowed, so they count. Sprays, butters and baths go on skin, and there's no good evidence they add meaningfully to the magnesium in your body.

• Supplements. Count the elemental magnesium on the label (for example, "magnesium 150 mg as magnesium glycinate"), not the weight of the whole compound.
• Electrolyte drinks and powders. Many contain magnesium. Check the panel per serve and multiply by the serves you actually drink.
• Medicines. Some antacids and laxatives are magnesium salts, such as magnesium hydroxide (milk of magnesia) and magnesium sulphate. The NIH counts these toward the upper limit (NIH ODS).
• Skin products. Magnesium sprays, flakes and creams are applied to the outside of the body.

### Does magnesium get through skin?

The honest answer: the evidence is weak and mixed. A 2017 paper by Gröber and colleagues, which pooled the published studies, concluded that the studies don't show magnesium is meaningfully taken up through skin, and that larger, well-designed trials would be needed (Gröber et al., 2017). A small 2017 pilot trial of a magnesium cream found a modest rise in serum magnesium in one subgroup, and only when athletes were excluded. It had 25 participants, one author declared a commercial interest in a magnesium cream, and the team called for larger studies (Kass et al., 2017).

That's why we sell our Magnesium Body Spray and Magnesium Bath Salts as body-care rituals for how they feel on skin, not as a way to get magnesium into your body. If you're running a magnesium bath, our guide to how much magnesium flakes per bath works the amount out by tub size. For the skin side of things, see why magnesium spray can sting and magnesium flakes vs Epsom salt.

What are the signs of too much magnesium?

Diarrhoea comes first, often with nausea and an upset stomach. Taking more than 400 mg for a short time can cause diarrhoea, according to the NHS (NHS). The NIH lists diarrhoea, nausea and stomach discomfort as the usual effects of high-dose supplements (NIH ODS).

True magnesium toxicity (hypermagnesaemia, too much magnesium in the blood) is rare. It usually involves very large doses of magnesium-containing laxatives or antacids, often alongside poor kidney function. Symptoms build with the blood level (StatPearls):

1. Nausea, flushing, headache and lethargy.
2. Drowsiness, weakness and loss of the reflexes a doctor checks with a hammer.
3. Dizziness or fainting, and a slow or irregular heartbeat.
4. In severe cases, breathing difficulty and cardiac arrest.

Who is most at risk from too much magnesium?

People whose kidneys can't clear it, and people taking high-dose magnesium medicines.

• Kidney disease. Reduced kidney function is the main risk factor for hypermagnesaemia (StatPearls). Don't take magnesium supplements or magnesium laxatives without your kidney team's advice.
• Heavy laxative or antacid use. Magnesium toxicity has been reported with doses of magnesium-containing laxatives and antacids well above the upper limit (NIH ODS).
• Older adults, whose kidney function often declines, and people with bowel conditions that change absorption (StatPearls).
• Medicine interactions. Magnesium can reduce the uptake of bisphosphonates (osteoporosis medicines) and tetracycline and quinolone antibiotics, so doses usually need to be spaced apart. Some diuretics and long-term proton pump inhibitors can lower magnesium in the blood instead (NIH ODS). Ask your pharmacist how to time them.

How common is low magnesium intake in each country?

Low intake is common in surveys, though low intake isn't the same as a diagnosed low blood level.

• Australia. In the ABS National Nutrition and Physical Activity Survey 2023, 31.3% of people aged 2 and over had an inadequate magnesium intake from food and drink: 35.2% of males and 27.3% of females. That's down from 34.9% in 2011–12. Rates were highest in men aged 75+ (50.2%) and teenage girls (43.9%). Supplements weren't included (ABS). The ABS notes the effects of too little magnesium are rare.
• New Zealand. NZ shares the NHMRC reference values. We didn't find a recent national magnesium figure we'd stand behind, so we're not quoting one.
• United States. An analysis of national survey data (NHANES 2005–06) found about half of Americans ate less magnesium than the Estimated Average Requirement (Rosanoff et al., 2012). The NIH notes that symptoms from low magnesium in otherwise well people are uncommon because the kidneys conserve magnesium (NIH ODS).
• Canada, the UK and South Africa. National diet surveys exist (Canada's CCHS–Nutrition, the UK's National Diet and Nutrition Survey), but we didn't find a single official headline magnesium figure to cite, and none for South Africa. The NHS view is that most people can get enough from a varied diet (NHS).

Only a blood test, interpreted by a doctor, can tell you whether your own levels are low. Blood levels don't always reflect the body's total stores, which is one reason doctors look at symptoms and history too (NIH ODS).

Using several magnesium products: what counts?

Add up what you swallow. Leave out what goes on your skin.

1. List every oral source. Tablets, powders, gummies, electrolyte drinks, fortified foods and any antacids or laxatives.
2. Read the elemental magnesium per serve on each label, then multiply by how many serves you take.
3. Compare the total with your country's limit. That's 350 mg for adults in AU, NZ, the US and Canada (65 mg for ages 1–3, 110 mg for ages 4–8). In the UK, the guidance is 400 mg or less. EU labels are based on 250 mg.
4. Don't count sprays, butters or baths. Topical products aren't included in any official upper limit, and the evidence for absorption through skin is weak (Gröber et al., 2017). They still need sensible use: patch test, and keep them off broken skin.
5. Talk to your doctor first if you have kidney disease, are expecting a baby, take regular medicines, or want to go over the limit. Some people are prescribed higher doses under a doctor's supervision.

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