How the European claim system works
In the EU only health claims that have been assessed and entered on an official list may be used on foods. Everything else is prohibited, however plausible it may sound.
What gets assessed is a specific substance in connection with a specific function and a minimum amount. An authorised claim therefore always belongs to a substance, never to a product name.
What applies to joint products
No authorised claim exists for glucosamine or MSM relating to joints, cartilage or mobility. Applications in this area were rejected because the evidence submitted was judged insufficient.
What is authorised is the vitamin C claim: it contributes to normal collagen formation for the normal function of cartilage. That is why products in this category almost always contain vitamin C, even though it is the smallest component by weight.
Structure versus healing
Authorised claims describe a nutrient contributing to a normal body function. They never describe relief of symptoms, reduction of inflammation or treatment of a disease.
Statements of the second kind are prohibited for foods in general, irrespective of the evidence. Reading one in product advertising means seeing a legal violation, not a proof.
A quick test for any advertisement
Take a claim and ask: does it name a substance or a product? Does it describe a normal body function or a complaint? Is the amount required for the claim stated?
If a claim concerns a product rather than a substance, or complaints rather than functions, it is not permitted in the EU. That is a fast and reliable test.