vitamin B vs B vitamin

vitamin B and B vitamin both are nouns.

Word	Noun	Adjective	Verb	Adverb
vitamin B	Yes	No	No	No
B vitamin	Yes	No	No	No

As nouns, vitamin B and B vitamin are synonyms defined as:

vitamin B and B vitamin: originally thought to be a single vitamin but now separated into several B vitamins

Other synonyms of vitamin B include B-complex vitamin, B, B complex, vitamin B complex.

vitamin B (noun)	B vitamin (noun)
originally thought to be a single vitamin but now separated into several B vitamins	originally thought to be a single vitamin but now separated into several B vitamins