Too much zinc: the 25 mg limit and what it means

The number in question is 25 milligrams a day. That is the tolerable upper intake level for zinc in adults, set by the European Commission's Scientific Committee on Food (SCF, 2003). Two properties of that number are regularly overlooked, and both decide whether there is anything to worry about: it means everything together — food, drinking water and supplement — and it means a permanent daily intake, not a single day.

And it is not a toxic threshold. The 25 mg are the result of a division: in the studies it rests on, around 50 mg of zinc a day over months produced nothing adverse — those 50 mg were then divided by a safety factor of 2. Anyone taking 30 mg on one day has therefore not "exceeded the limit" in the sense the word usually carries. Anyone taking 100 mg for years has.

Four numbers that end up on the same package

Four reference values circulate around zinc; all of them are correct and they answer three different questions. All of them refer to elemental zinc — not to the weight of the compound it comes from. Why that difference is unusually large with zinc is explained in Zinc forms compared.

Value	Amount	What it answers	Source
Nutrient reference value (NRV)	10 mg/day	What the % figure on the label is measured against	Regulation (EU) No 1169/2011, Annex XIII
Recommended intake	7–16 mg/day	How much an adult needs, graded by phytate intake	D-A-CH 2019
Tolerable upper intake level (UL)	25 mg/day	How much stays free of adverse effects long term	SCF 2003
Maximum level proposal for food supplements	6.5 mg/daily dose	How much the BfR considers appropriate in a supplement	BfR 2021

The gap between the third and the fourth row is not a contradiction but a design: the 25 mg apply to the sum, the 6.5 mg only to the addition — measured so that even someone with an already high zinc intake from food does not permanently end up far above 25 mg. The BfR additionally recommends that supplements with more than 3.5 mg of zinc per daily dose carry a note to avoid further zinc-containing preparations. The reason is sober: the derivation did not assume that anyone would take two of them.

Where the 25 mg come from

The critical point with zinc is not the zinc but the copper. The two metals compete in the gut. A high zinc intake stimulates the formation of metallothionein in the mucosal cells; this protein binds copper very tightly, and whatever stays bound inside the cell does not reach the body (Cousins, 1985). That is precisely the effect the SCF chose as the decisive endpoint. How this interplay works in detail, and from what amount it becomes practically relevant, is set out in Zinc and copper.

Three controlled studies were mainly evaluated: 25 and 21 post-menopausal women respectively received 53 mg of zinc a day for 90 days alongside an adequate copper intake (3 mg), and 19 healthy young men received a total of 40 mg over 14 weeks. In none of these investigations were clear adverse changes in copper balance, copper status, blood count or lipid metabolism detectable. From this the SCF derived a NOAEL — the highest amount with no observed adverse effect — of around 50 mg/day and divided by 2, because the participant numbers were small and the periods short. Result: 25 mg.

One side observation is remarkable, and many advice pages still report it differently: the activity of copper-dependent superoxide dismutase in the red blood cells does regularly fall when zinc is given — but the SCF expressly did not rate this fall as a sign of impaired copper status, because it occurred without accompanying adverse effects.

According to the SCF the 25 mg also apply in pregnancy and breastfeeding. For children and adolescents the value was converted via body surface area, for lack of data of their own:

Age	Tolerable upper intake level
1–3 years	7 mg/day
4–6 years	10 mg/day
7–10 years	13 mg/day
11–14 years	18 mg/day
15–17 years	22 mg/day

Why 40 mg appears elsewhere

Anyone reading up on English-language pages will find 40 mg given as the upper limit. That is not an error, nor a different body of evidence — it is the same body of evidence, assessed differently.

Body	Upper limit	Starting point	Factor
SCF (EU, 2003)	25 mg/day, all sources	NOAEL 50 mg/day	2
Institute of Medicine (USA, 2001)	40 mg/day, all sources	LOAEL 60 mg/day	1.5
EVM (UK, 2003)	25 mg/day, supplements only	—	—

The difference hangs on exactly the measure the SCF discarded: the Institute of Medicine treated the fall in superoxide dismutase as the adverse effect and relied on a study in which 18 women received 50 mg of zinc a day on top of their food for ten weeks. From "lowest amount with an observed effect" instead of "highest amount without an effect", plus a smaller safety factor, you get 40 instead of 25 mg. In practice that means: between 25 and 40 mg lies not a range in which something happens, but one on which two expert bodies disagree.

For Germany the EU figure nevertheless applies. Since 2021 the European Commission has instructed EFSA to revise its upper limits for a series of nutrients — vitamin A, folate, vitamin D, vitamin E, vitamin B6, selenium, iron, manganese and β-carotene. Zinc is not on that list; the 2003 value stands unchanged.

What a re-evaluation changes — the selenium example

How such a revision turns out can already be read off a trace element from the same list. For selenium EFSA delivered in 2023 what is still outstanding for zinc — and the value fell: from 300 to 255 micrograms a day for adults, including pregnant and breastfeeding women (EFSA Journal 2023;21(1):7704).

The arithmetic behind it is the same as for zinc, only with different numbers. The critical endpoint was hair loss — the earliest well-documented sign of excess selenium. From the SELECT trial, a large randomised controlled study, EFSA derived a LOAEL of 330 µg/day and divided by 1.3.

	Zinc	Selenium
Upper limit in the EU	25 mg/day	255 µg/day
Based on	NOAEL 50 mg/day	LOAEL 330 µg/day
Safety factor	2	1.3
State of the assessment	SCF 2003	EFSA 2023
Reference value (D-A-CH)	7–16 mg/day (recommended intake)	60 µg (women), 70 µg (men) — estimated value
Nutrient reference value (label)	10 mg	55 µg
BfR proposal for supplements	6.5 mg/daily dose	40 µg/daily dose

That the safety factor is smaller for selenium, even though the calculation started from an amount with an observed effect, has a sober reason: the SELECT trial covered tens of thousands of participants over years, while for zinc three small investigations with 19 to 25 people over weeks form the basis. The factor measures not how dangerous a substance is, but how robust the data are.

For the person standing in front of the shelf, exactly the pattern from this article repeats itself: the upper limit means the sum of everything, the BfR proposal only the addition from the supplement — and between the two lies a lot of room for misunderstanding. Our Selenium 100 µg contains 100 µg of selenium from selenium-enriched yeast per tablet, that is 182 % of the nutrient reference value: clearly above the BfR proposal of 40 µg, and at the same time far below the upper limit of 255 µg. EFSA names exactly two groups in which this upper limit is reached at all — regular users of high-dose selenium supplements and regular eaters of Brazil nuts. Anyone combining the two is better off doing the arithmetic than estimating.

What happens at genuinely high amounts

Here it pays to separate acute from long term, because the amounts lie an order of magnitude apart.

Acutely, zinc makes itself felt in the gastrointestinal tract: nausea, vomiting, upper abdominal pain, cramps, diarrhoea. The SCF refers to an estimate putting the emetic dose of zinc at 225 to 450 mg — that is ten to twenty times the upper limit in a single portion. The documented cases of acute zinc poisoning accordingly do not come from supplements but from foods and drinks stored in galvanised containers.

Long term, copper metabolism becomes the issue. Intakes of 50 mg to 300 mg a day over extended periods have been linked to a range of changes: lowered copper in the blood, reduced white blood cells and neutrophils, sideroblastic anaemia, reduced activity of copper-dependent enzymes, altered lipoprotein metabolism and impaired immune function. The unambiguous ones among these effects, however, appeared only above 150 mg/day over long periods; below 100 mg the critical effect is, in the SCF's assessment, hard to pin down.

How far away the acute danger lies is shown by a glance at medicine: in Wilson's disease, a copper storage disorder, 75 to 150 mg of zinc a day are used deliberately to throttle copper absorption — in individual patients for eleven years and longer, under medical supervision and without toxic effects. That is not an argument for high amounts without cause; it is a yardstick for what we are talking about.

How much already comes from food

The upper limit applies to the sum — so one has to know what the plate contributes. The German National Nutrition Survey II measured this for Germany:

Group	Median	95th percentile
Women 19–80 years	8.6–9.5 mg/day	13.7–15.5 mg/day
Men 19–80 years	10.4–12.3 mg/day	16.8–22.9 mg/day
Adolescents 14–18 years (f)	8.8 mg/day	15.8 mg/day
Adolescents 14–18 years (m)	11.9 mg/day	20.6 mg/day

From this follows the calculation anyone can do for themselves. An average eater lands at around 9 to 12 mg. A supplement with 6.5 mg brings them to about 16 to 19 mg — below the upper limit. A supplement with 25 mg brings them to 34 to 37 mg — above it. And in young men at the top of the intake range, the BfR's maximum level proposal alone is enough to arrive above 25 mg on paper (22.9 + 6.5 = 29.4 mg). That is precisely why the BfR advises against additionally fortifying general foods with zinc: there is simply no room left.

How much zinc actually arrives from a meal also depends on what lies beside it — phytate from wholegrains and pulses slows absorption considerably. The figures on that are in Zinc-rich foods.

What this means for a 25 mg supplement

Our Zinc 25 mg + vitamin B3 contains 25 mg of zinc per tablet — that corresponds to 250 % of the nutrient reference value and exactly to the tolerable upper intake level for adults. With what comes on top from a usual diet, the daily sum lies above it on paper, and clearly above the BfR's maximum level proposal for food supplements. That is not a footnote but the figure one should know before buying.

In practice that means three things: one tablet a day and no more; no further zinc-containing preparations alongside — including the multivitamin, which often already holds 10 to 15 mg; and over weeks and months such an amount is something different from over years. Anyone wanting to supplement permanently stays closer to what the expert bodies had in mind with a smaller daily amount. What else is in the range is shown by the Zinc category.

Authorised for zinc are, among others, these statements: Zinc contributes to the normal function of the immune system. Zinc contributes to normal cognitive function. Zinc contributes to normal fertility and reproduction. (Regulation (EU) No 432/2012). Food supplements are not a substitute for a balanced and varied diet and a healthy lifestyle.

Frequently asked questions

At what point is zinc toxic? Acute complaints set in, according to the estimate cited by the SCF, at about 225 to 450 mg in one portion. Permanent, unambiguous damage to copper metabolism is documented above 150 mg a day over long periods. The upper limit of 25 mg lies far below that — it marks not the onset of damage but the edge of what is well investigated, with a safety margin attached.

I accidentally took two tablets — what now? The tolerable upper intake level is a value for permanent daily intake, not a daily limit that snaps on a single day. 50 mg on one day is exactly the amount at which nothing was found in the studies over 90 days. It looks different if that becomes a habit.

Why do American pages say 40 mg? Because the Institute of Medicine took a different endpoint from the same studies and applied a smaller safety factor. In the EU the SCF's assessment applies, and with it 25 mg.

How would you notice too much zinc at all? Short term in the stomach and gut — nausea, cramps, diarrhoea, often within hours of taking it. The changes in copper metabolism, by contrast, are laboratory findings, not complaints one feels; they turn up at amounts one does not reach by accident. Anyone who has taken high amounts over a longer period and is unsure should have it clarified by a doctor rather than estimate.

Does the upper limit also apply in pregnancy? Yes. The SCF found no increased sensitivity and applies the same 25 mg a day to pregnant and breastfeeding women.

Are the upper limits of other trace elements built the same way? Yes, the procedure is identical: an amount from studies, divided by a safety factor. For selenium, for instance, a LOAEL of 330 µg/day divided by 1.3 gives an upper limit of 255 µg/day (EFSA 2023). Different factors reflect the state of the data, not the degree of danger — and because the data change, so do the figures: for selenium the upper limit fell in 2023 from 300 to 255 µg, while for zinc the value has stood since 2003.

Sources: SCF, "Opinion of the Scientific Committee on Food on the Tolerable Upper Intake Level of Zinc", SCF/CS/NUT/UPPLEV/62 Final, 19 March 2003 (full text) · BfR, "Höchstmengenvorschläge für Zink in Lebensmitteln inklusive Nahrungsergänzungsmitteln", 2021 · BfR, opinion 006/2024, "Aktualisierte Höchstmengenvorschläge für Vitamine und Mineralstoffe in Nahrungsergänzungsmitteln und angereicherten Lebensmitteln", 22 February 2024 · BfR, opinion 010/2024, "Aktualisierung (2023): Höchstmengenvorschläge für Selen in Lebensmitteln inklusive Nahrungsergänzungsmitteln", 22 February 2024 · EFSA NDA Panel, "Scientific opinion on the tolerable upper intake level for selenium", EFSA Journal 2023;21(1):7704 (full text) · D-A-CH, Reference Values for Nutrient Intake, zinc chapter (2019) and selenium chapter (2015) · Max Rubner Institute, German National Nutrition Survey II, results report part 2, 2008 · Regulation (EU) No 1169/2011, Annex XIII · Regulation (EU) No 432/2012 · Institute of Medicine, "Dietary Reference Intakes for … Zinc", 2001 (NCBI Bookshelf).