niacin vs vitamin B

niacin and vitamin B both are nouns.

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

As nouns, vitamin B is a hypernym of niacin; that is, vitamin B is a word with a broader meaning than niacin:

niacin: a B vitamin essential for the normal function of the nervous system and the gastrointestinal tract
vitamin B: originally thought to be a single vitamin but now separated into several B vitamins

Other hypernyms of niacin include B-complex vitamin, B, B complex, B vitamin, vitamin B complex.

niacin (noun)	vitamin B (noun)
a B vitamin essential for the normal function of the nervous system and the gastrointestinal tract	originally thought to be a single vitamin but now separated into several B vitamins