Which Is Better: NR or NMN?

 

Scientists have long known that NMN must be broken down into NR or NAM before it can enter the cell and replenish intracellular NAD:

 

Our results indicate that mammalian cells require conversion of extracellular NMN to NR for cellular uptake and NAD+ synthesis, explaining the overlapping metabolic effects observed with the two compounds.

-- Nature Communications, October 11, 2016

 

We also showed that extracellular cleavage of NAD+ and NMN to NR is a prerequisite for using these nucleotides to maintain intracellular NAD contents….The degradation of NAD+ and NMN to NR or Nam is essential for these nucleotides to act as extracellular precursors of intracellular NAD...

-- Metabolites, November 29, 2019

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That's why NMN only makes sense as a supplement if you do not have access to NR.

 

However, it has been suggested that an NMN transporter molecule, Slc12a8, might allow NMN to directly enter the cells, which could give NMN an advantage:

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Opposing views exist to Grozio et al.'s determination for Slc12a8 being an NMN transporter, Schmidt and Brenner point out that levels of NAD are 500 times higher than NMN in normal liver samples, and Grozio et al. (2019) had failed to examine background/control levels, which undermines any result Grozio et al. (2019) delivered. The debate remains open and no robust conclusion in this regard can be made.

-- Aging Medicine, August 4, 2021

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But Slc12a8 isn't well-expressed in all human cells, or even most human cells. So even if the transporter exists, NR would still be the better option for people trying to replenish NAD in their heart, nerves, muscles, eyes, and most or all other places.

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READ MORE about NMN v. NR...