Question about Niacin

[Sammie14]

Hello, hope all of you are doing well. I'm new to this world and already very confused. I read that people with a MTHFR mutation should not take Niacin, however, Niacin is in all complex B vitamins, even the ones made by Seeking Health. So is Niacin ok? It seems weird that the same doctor who said to stay away from Niacin would include them in his B Vitamins for people with MTHFR. Has anyone else wondered about this before or know what to do? Thanks in advance! I just want to start taking a good B vitamin that won't harm me.