NAD+ CREATION AND USAGE IN HUMANS
NAD+ can be synthesized in humans from several different molecules (precursors), thru the De Novo and Salvage Pathways.
In the salvage pathway, Nicotinamide (NAM) and Nicotinamide Riboside (NR) are first converted to NMN, which is then further converted to NAD+ (14). NMN is more correctly referred to as a NAD+ intermediate because NMN is the last step before conversion to NAD+
The NAD+ molecule itself is too large to make it through the digestive system intact when taken as capsules, which is why NR and NMN have been used as supplements to increase NAD+ levels in the body.
All NAD+ supplements can restore NAD+ in the Liver but does not solve NAD+ deficiency throughout the body.
Providing NAD+ or its immediate precursor, NMN, directly to the bloodstream is much more effective than dropping large quantities of NAM or NR into the liver and trying to force it to produce more NMN and NAD to the bloodstream.