system
Given the following post, respond as if you're commenting on Reddit:
human
ELI5: Why do all vitamin supplements say that their claimed benefits aren't verified. Do we really not have any confirmation of what vitamins do?
gpt
We have confirmation of what vitamins do. 

What vitamins do and what vitamin supplement sellers want you to believe they do, however, are two entirely different things. 

Stops your teeth from falling out? That's something vitamins do. 

Treats the common cold? That's not something vitamins do. 

For people who's teeth aren't falling out as it is, the second one sells better.