TABLE 2.

Comparison between the different NAD⁺ precursors.

NAD+ precursor	Advantages	Disadvantages	References
Niacin (NA)	- Prevents Pellagra - Regulation of lipid levels (total   cholesterol, triglycerides and LDL)	- Produces cutaneous   flushing - Not a NAD+ precursor in   the majority of the cells	Davidson, 2008; Guille et al., 2008; Prousky et al., 2011
Nicotinamide mononucleotide (NMN)	- One of the most used - Has shown an increase in NAD+   levels in the cell	- No consensus on how is   transported to the cell	Nikiforov et al., 2011; Grozio et al., 2019; Schmidt and Brenner, 2019
Nicotinamide (NAM)	Can be a stimulator in cells	Smaller increase in NAD+   compared to NR	Cantó et al., 2012
Nicotinamide riboside (NR)	- Action on   mammalian cells - Minimal toxicity - High bioavailability - High capacity to cross the blood-  brain barrier - Supports neuronal NAD+ synthesis - Greater ability to stimulate a   significant increase in NAD+ levels   and intermediate precursors	No evidence	Yang H. et al., 2007; Bogan and Brenner, 2008; Cantó et al., 2012; Trammell et al., 2016; Airhart et al., 2017; Martens et al., 2018