I'm very sus about this as well. And also, I just glanced at the NCBI article, but it reminded me that the degeneration that niacin seems to correct is something like Alzheimer's. My mother had Alzhiemer's (Dx in 1987 and died in 2001 -- awful disease).
I knew that is what she probably had, but she went into the hospital for 2 weeks to clarify her diagnosis. E.G. did she have a brain tumor that would account for her symptoms (complete memory loss, disorientation, paranoia, etc.) ... one thing they did along with a billion tests was give her Vitamin B (niacin) B3? injections. On occasion an older person will be short on such a nutrient as they just aren't eating properly.
Well, she didn't respond as that was not the problem.
As I always say, if niacin were a cure, individuals who take this to improve their cholesterol levels would be singing in the streets. I have to laugh as a "niacin" flush is a great way to get a man to understand "hot flashes."
Excessive doses of this can cause serious problems including stroke and death.
One anecdotal story like this ... I don't buy it. IMHO.