So you are taking a gram of regular Niacin daily. I will look for a source, but i do recall that Niacin, while it can be a precursor to NAD+ can also work in an opposite manner if there is too much in someone's metabolism.
I am sure you are more studied on this matter than myself, it is just that once i read that study, i now only take Niacin once a week or so.
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This isn't the post i was referring to, but it looks like an "it depends" scenario... as in, it depends on what your levels of NAD are... etc..
https://alivebyscience.com/forums/viewtopic.php?f=32&t=1419&p=4483&hilit=niacin#p4483