Aging cells run low on a small molecule called NAD+. That shortage drags down a family of repair enzymes called sirtuins. The SIRT1-NAD+ axis has become one of the most studied targets in longevity science.
What NAD+ Actually Does
NAD+ stands for nicotinamide adenine dinucleotide. It has a molecular weight of 663.43 g/mol. Every cell uses it as an electron carrier in metabolism, shuttling charge from food molecules into the mitochondrial machinery that makes ATP.
NAD+ is also a substrate, meaning enzymes consume it to do their jobs. Three big consumers are the sirtuins (SIRT1 through SIRT7), the PARPs that repair DNA, and the surface enzymes CD38 and CD157. When demand for NAD+ goes up, supply has to keep pace, or the entire network slows down.
SIRT1 as the Master Regulator
SIRT1 is the best-studied sirtuin. It strips small chemical tags called acetyl groups off proteins, which changes how those proteins behave. Through this action, SIRT1 tunes hundreds of targets involved in inflammation, metabolism, mitochondrial production, and stress resistance.
Verdin (2015) reviewed how this network ties together aging, metabolism, and neurodegeneration. When NAD+ levels drop, SIRT1 cannot keep up with its workload, and the cell loses some of its tuning ability. Many features of older tissue look like a SIRT1 deficit.
Why NAD+ Levels Fall With Age
NAD+ does not just disappear. It is consumed faster than the cell can rebuild it. CD38 activity rises with age and chronic inflammation, which burns through NAD+. PARPs also draw heavily on NAD+ to fix accumulating DNA damage.
Yoshino et al. (2011) showed that restoring NAD+ in aged mice normalized glucose tolerance and improved mitochondrial function. The work suggested that the deficit, not the calendar, was driving part of the metabolic decline. Gomes et al. (2013) added a deeper twist, showing that falling NAD+ disrupts SIRT1-HIF1alpha signaling and creates a "pseudohypoxia," a state where cells act oxygen-starved even when oxygen is fine.
Where Peptides Enter the Story
Several research peptides plug into this axis. MOTS-c, a peptide encoded inside mitochondrial DNA, activates AMPK and indirectly supports NAD+-dependent signaling. Other tools used in aging labs aim to spare NAD+ by reducing PARP overactivation or by tuning CD38.
NAD+ itself, along with its precursors, is studied as a direct intervention. Researchers track changes in tissue NAD+ levels, sirtuin activity, mitochondrial output, and inflammatory markers. The goal is to see whether boosting the substrate restores the downstream network.
Open Questions
The axis is promising but messy. Tissues differ in how they make and use NAD+, so a strategy that works in liver may underperform in brain. Long-term safety questions also remain, since some sirtuins and PARPs play roles in cancer biology, and shifting their activity is not always benign.
Researchers are still mapping out the best precursors, the best timing, and which combinations of peptides and small molecules deliver the most consistent effect. The basic biology is solid, but translating it into reliable interventions takes time. These compounds are sold strictly for in vitro laboratory research and are not approved for human consumption.