system
Given the following post, respond as if you're commenting on Reddit:
human
ELI5: What is the significance of the letter in the title of vitamins e.g. vitamin A?

Also, why are there so many different vitamin B's?
gpt
Vitamins were named alphabetically according to which ones were discovered first. There are so many different vitamin Bs because at first all of the different types were thought to be very similar and all called "vitamin B". Later it was found that they serve different biological functions and were renamed. All the vitamin Bs together are called vitamin B complex, by the way. As for the missing gaps (B12 existing when there are only 8 types of B vitamins, the jump from vitamin E to vitamin K), those are from substances that were thought to be vitamins being named, then discarded after scientists realized that they didn't classify.