Hypothesis

Intermittent rapamycin dosing upregulates the NAD+ salvage enzyme NAMPT in peripheral tissues, thereby increasing the conversion of supplemented NMN or NR into functional NAD+ pools where blood NAD+ rises fail to reflect tissue changes.

Mechanistic Rationale

• Rapamycin inhibits mTORC1, which reduces CD38 expression and NAD+ consumption, while stimulating autophagy that recycles nicotinamide substrates.
• This creates a cellular environment where exogenous NAD+ precursors are preferentially shunted into the salvage pathway rather than being degraded.
• Consequently, intermittent rapamycin should amplify tissue NAD+ elevation from NMN/NR beyond the ~2-fold increase seen in blood alone.

Testable Predictions

1. In a randomized crossover trial, participants receiving 2 g NMN daily plus intermittent rapamycin (2 mg weekly) will show a ≥30 % greater increase in muscle NAD+ (measured by biopsy or MR spectroscopy) after 4 weeks compared to NMN alone, while blood NAD+ remains similarly elevated.
2. GrimAge (or DunedinPACE) will improve by at least 0.5 years of epigenetic age reversal after 8 weeks of the combined regimen, whereas NMN or rapamycin alone produce <0.2 years change.
3. The effect will be blunted in subjects with genetically high CD38 activity, supporting the mechanistic link.

Falsifiability

If muscle NAD+ does not differ significantly between groups, or GrimAge shows no superior improvement, the hypothesis is refuted.

Practical Note

Quarterly self‑monitoring with epigenetic clocks is feasible because the predicted changes exceed the typical test‑retest variability (~0.3 years) reported for GrimAge.

References

• NMN/NR blood NAD+ elevation: NMN.com news on NAD+ precursor trial
• NR vs NMN potency: NAD.com article on NR raising NAD+ over 2‑fold
• Intermittent rapamycin dosing benefits: Rapamycin.news discussion on intermittent feeding