Two supplement labels, the same nutrient, two completely different numbers. One says 125, the other says 5000. One says 250 mg of magnesium citrate, the other says 251 mg of elemental magnesium. One says 400, the other says 200 for what looks like the same vitamin. Usually nobody is lying. Under EU law a figure on a supplement label is defined by three things at once: the unit it is expressed in, the portion it is counted against, and the fact that it is an average rather than a promise. Once you know which of the three is moving, the confusion resolves in about a minute.
The short answer
Two labels can print different numbers for the same nutrient, in the same amount of product, for six legitimate reasons: they use different units, they count per capsule instead of per daily portion, one weighs the mineral salt and the other the mineral inside it, the printed value is a legal average with a tolerance band around it, manufacturers add an overage so the number still holds at the end of shelf life, and the maximum dose allowed is set nationally rather than at EU level. Only the percentage of the nutrient reference value, printed next to the amount, puts two labels on a common scale.
Reason 1: the two labels are not using the same unit
This is the biggest single source of confusion, and it is written into the law. Article 8(1) of Directive 2002/46/EC says the amount of each nutrient must be declared in numerical form and that "the units to be used for vitamins and minerals shall be those specified in Annex I". That annex does not use one neutral unit for everything. It declares vitamin A in micrograms RE (retinol equivalents), vitamin E in milligrams alpha-TE (alpha-tocopherol equivalents), niacin in milligrams NE (niacin equivalents), vitamin D and vitamin K in plain micrograms, and folic acid in micrograms, with a footnote stating that the term "folic acid" here covers all forms of folates.
Three of those units are equivalence units. They already contain a conversion, because the vitamin exists in several chemical forms with different biological activity, and the law wants one comparable figure instead of a list. So "40 mg NE" of niacin is not simply 40 mg of a substance: it is 40 mg expressed on the niacin equivalent scale.
The unit that is not in EU law at all
International Units (IU) appear on a great many supplement labels, especially for vitamin D. IU is not one of the units in Annex I. It is a legacy biological activity unit, and for vitamin D the conversion is fixed: the biological activity of 1 microgram of vitamin D is equivalent to 40 IU, as set out in the Institute of Medicine reference report on calcium and vitamin D.
That single conversion explains an enormous amount of shelf confusion. A label reading 125 µg and a label reading 5000 IU describe exactly the same amount of vitamin D. The second number is forty times larger and the product is not stronger. Our own Vitamin D3 + K2 drops print both: the supplement panel declares 125 µg, which is the legally required unit, and the product name carries 5000 IU, because that is the number people search for.
Reason 2: the denominator is not the same
A number is meaningless without knowing what it is counted against, and here supplements follow a different rule from ordinary food. For general foods, Article 32(2) of Regulation (EU) No 1169/2011 requires the nutrition declaration to be expressed per 100 g or per 100 ml. For food supplements, Article 8(2) of Directive 2002/46/EC requires something else entirely: the amounts declared "shall be those per portion of the product as recommended for daily consumption on the labelling". Article 6(3)(b) of the same directive makes stating that portion mandatory.
So the legal denominator on a supplement is the daily portion, not the capsule. If one brand's portion is two capsules and another's is one, and both print 300 mg, the first brand gives you 150 mg per capsule and the second 300 mg. Same printed number, half the strength per unit swallowed, and a completely different cost per day once you count how long a tub lasts.
Some labels helpfully print both a per capsule and a per portion column. Many print only the portion. If a panel gives a number without telling you the portion it belongs to, that is the first thing to look up, not the last.
Reason 3: the mineral is only part of what is being weighed
Minerals are never sold as bare metal. They arrive bound to something: picolinate, bisglycinate, citrate, oxide. The compound weighs far more than the mineral inside it, so "500 mg magnesium citrate" and "500 mg magnesium" are different statements about very different amounts. The figure that matters is the elemental one, and it is normally the figure carrying the percentage.
We have covered this arithmetic in detail before, so here it is enough to know it exists and where to look: see which form of magnesium is best absorbed for the worked comparison. Our Magnesium 7 in 1 panel lists each salt separately and then states the elemental total, 251 mg, which is the number to compare against another brand.
Reason 4: the printed number is an average, not a promise
This is the part most people never hear, and it changes how you should read every supplement panel you have ever picked up.
Article 9(1) of Directive 2002/46/EC states that "the declared values mentioned in Article 8(1) and (2) shall be average values based on the manufacturer's analysis of the product". Regulation (EU) No 1169/2011 says the same for foods in Article 31(4): declared values shall be average values based on the manufacturer's analysis, on a calculation from the known or actual average values of the ingredients used, or on a calculation from generally established and accepted data.
An average is not a floor and not a ceiling. It is the value that best represents what the product contains across batches, allowing for natural variation in raw materials, in manufacturing and during storage. The tub in your hand is one sample from that distribution.
How far the real content may legally drift
Because a declared value is an average, official controls need a band around it before they can call a product non-compliant. The European Commission published that band in December 2012, in its guidance document for competent authorities on the setting of tolerances for nutrient values declared on a label. Food supplements get their own table, and the tolerances already include measurement uncertainty, so no further allowance is added when a laboratory result is judged.
| Product type | Vitamins | Minerals |
|---|---|---|
| Food supplements | +50% to -20% | +45% to -20% |
| Foods other than food supplements | +50% to -35% | +45% to -35% |
Read the top row slowly. A food supplement declaring 100 µg of a vitamin is, on an official check, compliant anywhere between 80 µg and 150 µg. Supplements are held to a tighter lower limit than ordinary foods, 20% below the declaration instead of 35%. The same guidance sets out why the real content drifts at all: the source of the values (calculated from a recipe rather than analysed), the accuracy of the analysis, variation in the raw materials, the effect of processing, nutrient stability, and storage conditions and storage time.
The guidance also blocks the obvious abuse. It states that declared values should approximate to the average values across multiple batches and "should not be established at either extreme of a defined tolerance range", and that for nutrients where consumers want higher levels, the declared value should not sit at the top of the tolerance range while the true average is lower. Where a national maximum amount exists, that maximum takes priority over the upper end of the tolerance range.
Reason 5: overage, and the clock running on the tub
The declared value has to hold until the end of shelf life, and most vitamins slowly degrade. The standard answer is overage: the manufacturer formulates above the label figure so the product still meets its declaration on the last day of its date. That is not a trick, it is how a stable declaration is achieved, but it does mean a fresh tub can genuinely contain more than it says.
How much more is not theoretical. In a pilot study by the Dutch National Institute for Public Health and the Environment (RIVM), published in Food Chemistry in 2017, researchers analysed vitamin D in products intended for infants and found measured content ranging from 8% to 177% of the declared value across 15 dietary supplements, and from 50% to 153% across 29 fortified foods. The authors named overages to cover shelf life losses as a reason the actual concentration may deviate from the label, and concluded that using label information alone may give invalid estimates of real intake. That study looked at infant products, not the whole market, so treat it as a demonstration that the gap is real rather than as a figure for your own tub. Storage matters here too, which is why we wrote separately about heat, light and humidity.
Reason 6: the ceiling is national, not European
If the same brand sells what looks like the same product at a different dose in Germany and in the Netherlands, that is not necessarily marketing. Maximum amounts for vitamins and minerals in food supplements have never been harmonised across the EU. The Commission's tolerance guidance says so plainly: in the absence of harmonised rules on maximum amounts in foods and food supplements, Member States may establish national rules. So the legal ceiling a formulator has to work under depends on the country, and the printed number moves with it.
The one column that makes two labels comparable
Article 8(3) of Directive 2002/46/EC requires that information on vitamins and minerals is also expressed as a percentage of the reference values. Those values now live in Part A of Annex XIII to Regulation (EU) No 1169/2011, the nutrient reference values (NRVs). A selection, so you can check any panel yourself:
- Vitamin A 800 µg, vitamin D 5 µg, vitamin E 12 mg, vitamin K 75 µg, vitamin C 80 mg
- Thiamin 1,1 mg, riboflavin 1,4 mg, niacin 16 mg, vitamin B6 1,4 mg, folic acid 200 µg, vitamin B12 2,5 µg, biotin 50 µg, pantothenic acid 6 mg
- Calcium 800 mg, magnesium 375 mg, iron 14 mg, zinc 10 mg, iodine 150 µg, selenium 55 µg
The percentage is the great equaliser, because it is calculated per daily portion, after the unit conversion, on the elemental amount. Two labels printing 125 µg and 5000 IU both come out at 2500% of the vitamin D NRV. That is the number to compare, not the headline. What the percentage does not tell you is whether you personally need that much, which is a separate question we answered in what %NRV actually means.
Comparing two labels in under a minute
- Find the portion. Read what one daily portion is on each label before you read a single number. If the portions differ, nothing else is comparable yet.
- Match the units. If one says IU and the other micrograms, convert before judging. For vitamin D, divide the IU figure by 40.
- Take the elemental figure for minerals. Ignore the salt weight. If only the salt is named with no elemental figure, that is itself a finding.
- Read the percentage, then the price per day. Divide the pack price by the number of daily portions. A tub with a bigger headline number can easily cost more per day for the same delivered amount.
What this looks like on our own labels
We ran the same check on our own panels, because an article like this is worthless if the author will not apply it to himself.
The arithmetic reconciles. Our D3 + K2 drops declare 125 µg of vitamin D3, which is 2500% of the 5 µg NRV, and 120 µg of vitamin K2 as MK-7, which is 160% of the 75 µg NRV. The bioactive B-complex declares vitamin B12 at 500 µg, or 20000% of the 2,5 µg NRV, and niacin as 40 mg NE, using the niacin equivalent unit exactly as Annex I requires. Our zinc picolinate declares 30 mg of elemental zinc, 300% of the 10 mg NRV.
Two honest observations about our own presentation. First, we do exactly what this article describes as confusing: the D3 product is named 5000 IU while its panel declares 125 µg. We keep the IU in the name because that is the number customers search for, but the legal declaration, and the one you should compare, is the microgram figure. Second, our magnesium panel lists each of the seven salts by weight and then states the elemental total of 251 mg separately, which is 67% of the 375 mg NRV. That layout is the whole point of reason 3, and it is why the individual salt weights should never be added together and read as a magnesium dose.
Frequently asked questions
If two labels show the same number, do the products contain the same amount?
Not necessarily. The same number can sit on a different unit, a different daily portion, or a mineral salt rather than the elemental mineral. And because declared values are averages with a legal tolerance band, two products both declaring 100 µg of a vitamin can lawfully measure 80 µg and 150 µg on the same day.
Is the label a minimum amount?
No. Under Article 9(1) of Directive 2002/46/EC the declared value is an average based on the manufacturer's analysis. For vitamins and minerals in food supplements, the Commission's tolerance guidance allows a measured value down to 20% below the declaration before it counts as non-compliant, with measurement uncertainty already included in that figure.
Why does my label say IU when the law asks for micrograms?
Because both can appear. Annex I of Directive 2002/46/EC sets the mandatory unit, which for vitamin D is micrograms. IU is a legacy unit that many brands keep alongside it for recognition. It is additional information, not the legal declaration, and 1 microgram of vitamin D corresponds to 40 IU.
Is a higher number automatically better?
No. A high number on a poorly absorbed compound can deliver less than a lower number on a well absorbed one, and above the point where a nutrient is replete, more stops adding anything. The percentage of the NRV tells you how the dose relates to a labelling reference, not to your own requirement.
Why is the same product sold at a different strength in another EU country?
Because maximum amounts for vitamins and minerals in food supplements are not harmonised at EU level. The Commission's guidance notes that in the absence of harmonised rules, Member States may set national rules, and a national maximum takes priority over the top of the tolerance range.
Does any of this mean brands are cheating?
Mostly it does not. Units, portions, salt weights and averages are all written into EU law, and a manufacturer following them exactly will still print a number that looks nothing like a competitor's. The check that separates a careless label from a careful one is whether it gives you a portion, an elemental figure and a percentage, so you can do the arithmetic yourself. A batch certificate, if the brand publishes one, is the next layer down: see what a certificate of analysis actually proves.
The Bottom Line
A supplement number is not a fact on its own. It is a value in a specific unit, counted against a specific daily portion, referring either to a compound or to the element inside it, and legally defined as an average with a tolerance band around it. That is why two honest brands can print 125 and 5000 for the same amount of vitamin D, or 500 mg and 251 mg for magnesium doses that are closer than they look. Read the portion, convert the unit, find the elemental figure, then let the percentage do the comparing. It takes a minute and it is the difference between buying a headline and buying a dose.
Sources
- Directive 2002/46/EC on food supplements, Articles 6, 8 and 9 (labelling particulars, units from Annex I, declaration per recommended daily portion, percentage of reference values, declared values as average values based on the manufacturer's analysis).
- Directive 2002/46/EC, Annex I, as substituted by Commission Regulation (EC) No 1170/2009 (vitamin A in µg RE, vitamin E in mg alpha-TE, niacin in mg NE, folic acid in µg covering all forms of folates).
- Regulation (EU) No 1169/2011, Annex XIII Part A, daily reference intakes for vitamins and minerals (adults), the nutrient reference values quoted above.
- Regulation (EU) No 1169/2011, Article 31(4), declared values shall be average values.
- Regulation (EU) No 1169/2011, Article 32, expression per 100 g or per 100 ml for foods other than supplements.
- European Commission, Guidance document for competent authorities for the control of compliance with EU legislation on the setting of tolerances for nutrient values declared on a label, December 2012 (Table 2 for food supplements, the average value principle, the rule against declaring at either extreme, and national maximum amounts).
- European Commission, Guidance document tolerances: simplified summary table, December 2012.
- Verkaik-Kloosterman J, Seves SM, Ocké MC. Vitamin D concentrations in fortified foods and dietary supplements intended for infants: implications for vitamin D intake. Food Chemistry, 2017 (PMID 27979251), measured vitamin D from 8% to 177% of the declared value in 15 supplements, with overages named as a cause.
- Institute of Medicine, Dietary Reference Intakes for Calcium and Vitamin D, 2011, overview of vitamin D, the biological activity of 1 microgram of vitamin D is equivalent to 40 IU.
A note on sourcing: EUR-Lex serves an empty response to automated requests, so the EU legal texts above are linked through the legislation.gov.uk mirror, which reproduces the instruments as published by the EU. The instruments themselves are named in full so any figure can be checked against the official Official Journal text.
