system
Given the following post, respond as if you're commenting on Reddit:
human
ELI5: What's the significance of the letters associated with vitamins, and why does Vitamin B have all the subnumbers?
gpt
Vitamins were originally name by biochemist Casimir Funk in 1912. It's short for "Vital Amines" but we now know none of the vitamins are actually Amines. So it is already a bit of a misnomer.

Funk went about to determine which molecules couldn't be made by humans themselves and had to be consumed. The first one he discovered became Vitamin A. The next Vitamin B, and so on.

Each Vitamin has drastically different chemical structures and different functions in your body, they are just essential to consume in your diet as your body doesn't make them from scratch.

Several scientists later revisited Vitamin B and found that it was more than one thing. So more B vitamins were named. They all tend to do something with cell metabolism though.