Once you know what "source of", "high in" and an authorised health claim actually mean, most supplement marketing gets a lot easier to see through.
Most label claims are more regulated than you think
There's a persistent idea that supplement labelling is the Wild West - that any brand can claim anything it likes and nobody checks. In the UK and EU, that's largely not true, and knowing why is the single most useful piece of label literacy you can have. Nutrition and health claims on food and supplement labels are governed by Regulation (EC) No 1924/2006, and any claim about what a nutrient does in the body has to be either an authorised health claim that's been scientifically assessed, or a nutrition claim that meets a specific, legally defined threshold. Once you know the categories, a label stops being marketing copy and starts being something you can actually read.
What "authorised health claim" actually means
An authorised health claim isn't a marketing team's phrase - it's wording that has gone through a formal scientific assessment (in the UK and EU, run by EFSA) and been written into law with specific conditions attached. Creatine's claim for adults over 55 is a good example of how specific these get: the authorised wording is "daily creatine consumption can enhance the effect of resistance training on muscle strength in adults over the age of 55," and it only applies at a 3g daily dose, combined with resistance training at least three times a week. A brand can't shorten that to a vaguer, punchier claim and still be using the authorised wording correctly - the whole claim, including its conditions, is what's authorised, not just the memorable bit.
Vitamin D's claims work the same way: normal muscle function, normal bone, normal teeth, normal immune system function are all separately authorised claims, each requiring the nutrient to be present at a defined significant amount per serving. Protein's authorised claim - contribution to the maintenance of muscle mass - has its own defined threshold too. When you see one of these claims on a label, you're reading something that's been checked, not just written.
NRV, and what "source of" versus "high in" actually require
NRV stands for Nutrient Reference Value - the standardised reference amount used across the UK and EU to express how much of a vitamin or mineral a serving provides, shown as a percentage. It's the same reference figure for everyone, which is what makes it possible to compare one product's vitamin D content against another's on a like-for-like basis, rather than each brand inventing its own scale.
"Source of [nutrient]" and "high in [nutrient]" are nutrition claims, not health claims, and each has a specific legal threshold. A "source of" claim requires at least 15% of the NRV per serving (or per 100g/100ml for some foods). A "high in" claim requires at least twice that - 30% of the NRV per serving. These thresholds are fixed in law, so when you see "high in vitamin D" on a label, that's a specific, checkable promise about quantity, not a subjective description.
Spotting a claim that hasn't earned its place
Here's where label literacy actually pays off. An authorised health claim reads like defined, specific wording - "contributes to normal muscle function," "helps maintain normal bone" - because it is defined, specific wording, lifted from the regulation itself. A claim that hasn't gone through that process usually reads differently: broader, more emotive, and structured around an outcome rather than a defined bodily function. Phrases like "supports joint health," "boosts recovery," or "helps you feel younger" aren't authorised health claim wording, because no such generic claims exist in that form - health claims are always tied to a specific nutrient, a specific function, and often a specific population or dose.
That doesn't automatically mean a product is dishonest. Plenty of genuinely well-evidenced ingredients - turmeric and joint comfort research is a good example - don't have an authorised claim yet, simply because the specific evidence bar EFSA requires hasn't been cleared for that exact wording. The honest way to write about those ingredients is to describe what a specific, cited study found ("a 2025 trial found X"), not to imply an approved claim that doesn't exist. When you're reading someone else's label, the tell is the reverse: if the phrasing sounds like an outcome promise rather than a defined bodily function, with no study or citation anywhere nearby, that's worth treating with more scepticism than a specific, dosed, authorised claim.
Reading is a skill, like anything else you've trained for
You wouldn't take a training plan at face value without checking the reasoning behind it, and a supplement label deserves the same scrutiny. Once you can tell an authorised claim from a nutrition claim from an unsubstantiated one, you're not relying on a brand's tone of voice to decide what to trust - you're reading the actual regulatory content underneath it. That's a skill worth having for the same reason good training logs are worth keeping: it's how you make decisions on evidence, not on how something's been packaged.
Sources
- Regulation (EC) No 1924/2006 of the European Parliament and of the Council on nutrition and health claims made on foods. - https://eur-lex.europa.eu/legal-content/EN/TXT/?uri=CELEX%3A32006R1924
- Commission Implementing Regulation (EU) 2017/672 of 7 April 2017 (creatine and muscle strength claim, adults over 55). - https://www.legislation.gov.uk/eur/2017/672/data.html
- EU Register of nutrition and health claims made on foods (European Commission). - https://ec.europa.eu/food/safety/labelling_nutrition/claims/register/public/
- Commission Regulation (EU) No 1047/2012 amending Regulation (EC) No 1924/2006 with regard to the list of nutrition claims. - https://eur-lex.europa.eu/legal-content/EN/TXT/PDF/?uri=CELEX:32013R1066&from=EL