B vitamin vs vitamin B complex

B vitamin and vitamin B complex both are nouns.

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

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

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

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

B vitamin (noun)	vitamin B complex (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