NMN vs NR: which NAD+ precursor is better?

Short Answer: Both NMN and NR effectively raise blood NAD+ levels. NMN may have a slight edge due to a recently discovered direct cellular transporter (Slc12a8), while NR must first convert to NMN. Clinical differences are minimal.

Evidence Level: moderate

Detailed Answer

Nicotinamide mononucleotide (NMN) and nicotinamide riboside (NR) are both NAD+ precursors that restore age-related NAD+ decline. NR was long assumed superior because NMN was thought to require extracellular conversion to NR before cellular uptake. However, Grozio et al. (2019, Nat Metab) discovered Slc12a8, a specific NMN transporter in the small intestine. Both raise blood NAD+ levels effectively in human trials: NMN 250mg/day increased NAD+ ~40% (Yoshino et al., 2021, Science); NR 1000mg/day increased NAD+ ~60% (Airhart SE et al., 2017). NR has more published human safety data (ChromaDex/Niagen). NMN may have better stability and doesn't require conversion steps. Key consideration: both are eventually metabolized to NAD+ through the same salvage pathway. The best choice may depend on price, formulation quality, and individual response rather than fundamental biochemistry.

Sources

• Yoshino J et al. (2021) Science — NMN human trial
• Grozio A et al. (2019) Nat Metab — Slc12a8 transporter