Reading the label of a food supplement
Two boxes can display the same name and have almost nothing in common. Everything is decided on the back, in small print. Here's how to read a food supplement label line by line, and what truly deserves your attention before comparing two products.
The dose per day, not the dose per capsule
The first column of a values table almost always shows the content for the recommended daily dose, not for a single capsule. If the box recommends three capsules a day, the figures shown correspond to all three combined. That's the first trap: a product that seems highly dosed may simply require swallowing several.
So look first at the line daily dose or serving, at the top of the table, then relate everything else to that number. To compare two products honestly, you have to bring each back to the same basis: the actual content provided over a day, and the number of doses that this involves.
NRVs: what the percentage means
Next to each vitamin or mineral there is a percentage. It relates to the nutrient reference values (NRVs), European benchmarks that correspond, roughly, to the needs of an average adult1,2. An intake at 100% of the NRVs covers this benchmark; 50% covers half of it; 200% double.
These percentages are useful for situating a product, but they have their limits. The NRVs are averages, the same for everyone, whereas needs vary with age, sex and lifestyle. Some nutrients have no established NRV and are then shown in milligrams alone. A very high percentage is not necessarily a mark of quality: beyond a certain threshold, the body doesn't use more, and a few nutrients have limits not to be exceeded.
The information that matters is not on the front: it's on the back, in the actual dose over a day, the form of the nutrient and the length of the ingredient list.
The form of the nutrient changes everything
Two products can display magnesium 300 mg and not be equivalent, because what matters is the chemical form used. A mineral is almost always supplied in the form of a salt: oxide, citrate, bisglycinate for magnesium; gluconate, bisglycinate or sulfate for zinc. These forms do not provide the same amount of usable mineral and are not absorbed in the same way3,4.
A carefully made label specifies the form in parentheses. For vitamins too, the form matters: vitamin D exists as D2 and D3, vitamin B9 as folic acid or already-active folates. Spotting these details makes it possible to compare what is truly comparable, and to understand why two products with the same name display different prices.
Excipients and the ingredient list
Below the nutrient table, the ingredient list reveals the rest: the excipients that give shape to the capsule or tablet, the coating agents, the colorings, the flavorings. They are listed in order of decreasing weight. A short list, with readable names, is generally a good sign.
You will also find the capsule shell, of plant or animal origin, which is of interest to vegetarians, and the mention of any allergens. This is where superfluous additives can be spotted. A supplement does not need a long list of auxiliaries to fit in a capsule.
Claims: what a brand is allowed to write
Phrases such as contributes to the normal functioning of the nervous system are not free to use: they are authorised health claims, regulated at the European level, and each is tied to a specific nutrient and a minimum dose. A brand may only use them if the product reaches that dose.
On the other hand, no food supplement is allowed to promise to cure, treat or prevent a disease: that falls to medicines. A label that stays within the register of normal functioning and of maintenance respects the framework. Spectacular promises, on the contrary, should arouse suspicion.
Storage, date, and what else to check
Finish with the practical details: the date of minimum durability, the storage conditions (away from light and moisture, sometimes refrigerated), and the precautions for use, particularly for pregnancy or combination with other products.
One last useful habit: keep the label, or a photo, so you can show it to a healthcare professional if you have a question5. A pharmacist reads these tables every day and spots at a glance what deserves attention. Reading a label is in no way reserved for specialists: a few markers are enough to compare, to understand, and to choose without relying only on the front.
References
- Dietary Reference Values for nutrients, Summary report. EFSA Supporting Publications, 2017. efsa.europa.eu
- Dietary reference values (thematic dossier). European Food Safety Authority (EFSA), accessed 2026. efsa.europa.eu
- Meta-analysis of calcium bioavailability: a comparison of calcium citrate with calcium carbonate. American Journal of Therapeutics, 2001. pubmed.ncbi.nlm.nih.gov
- Higher bioavailability of magnesium citrate as compared to magnesium oxide. BMC Nutrition, 2017. link.springer.com
- Vitamin and Mineral Supplement Fact Sheets. Office of Dietary Supplements, National Institutes of Health, accessed 2026. ods.od.nih.gov