As for NAD+ injections, there are many celebrity promoters who include Gwyneth Paltrow, Kendall Jenner, Jennifer Aniston, Halle Berry, Joe Rogan, Hailey Bieber, and Justin Bieber
This means that it is not possible to overdose on vitamin B12, and as far as we know there is no upper limit on the amount of B12 that can be taken safely by an otherwise healthy person
Increased expression of the immediate response gene, early growth response gene-1 (egr-1), was shown in Caco-2 cells in vitro (Tkalcevic et al., 2007)
and 3-numerous confluent changes subcategorized into: (a) the hemorrhagic zone, (b) edema, (c) the loss of neurons, (d) vacuoles, and (e) the loss of spinal column tracts [3]
However, during a severe viral infection or prolonged periods of chronic inflammation, this vital defense system can become overwhelmed and depleted