Sirtuins are the reason anyone cares about NAD+ for aging rather than just for metabolism. They are also the part of the story where the marketing has drifted furthest from the evidence, so it is worth separating what is established from what got oversold a decade ago and never corrected.
The one-paragraph version
Sirtuins are a family of enzymes that regulate stress responses, metabolism and DNA repair — and they cannot work without consuming NAD+. That dependency is solid biochemistry and it is the strongest mechanistic argument for keeping NAD+ available. What is far less settled is whether boosting sirtuin activity in a healthy adult produces an outcome you would notice.
What they are
Mammals have seven sirtuins, labelled SIRT1 through SIRT7. They are not interchangeable — they sit in different parts of the cell and act on different targets.
- SIRT1 — nucleus and cytoplasm. The best studied. Acts on regulators involved in metabolic and stress responses.
- SIRT2 — mainly cytoplasmic, with roles in the cell cycle.
- SIRT3, 4 and 5 — mitochondrial. SIRT3 in particular acts on enzymes of energy metabolism, which is why it comes up in discussions of mitochondrial function.
- SIRT6 and SIRT7 — nuclear, with roles in DNA repair and genome maintenance.
The NAD+ dependency, precisely
This is the mechanistically important part, and it is worth being exact about it, because the imprecise version is what gets oversold.
Sirtuins are usually described as deacetylases: they remove acetyl groups from protein targets, which changes how those proteins behave. But they do not simply detach an acetyl group and move on. The reaction requires NAD+ as a co-substrate and destroys it, cleaving off nicotinamide and transferring the acetyl group onto the remaining ADP-ribose.
So every sirtuin reaction costs one NAD+. Not borrowed — spent. That makes sirtuin activity directly limited by how much NAD+ is available, which is the entire mechanistic basis for taking a precursor.
Where the story got ahead of itself
Two things in the sirtuin literature were presented with more confidence than they turned out to deserve, and both still circulate.
The resveratrol activation claim
Resveratrol was widely reported to activate SIRT1 directly, which launched an enormous supplement category. The original findings relied on an assay using a fluorescent tag attached to the substrate, and later work indicated the apparent activation depended on that tag rather than occurring with native substrates. The question of whether resveratrol meaningfully activates SIRT1 in a person remains contested. The supplement market moved on as though it had been settled.
The lifespan-extension results
Early reports that extra sirtuin activity extended lifespan in yeast, worms and flies were influential. Subsequent replication attempts with better-controlled genetic backgrounds substantially reduced or eliminated several of those effects. Sirtuins remain genuinely important regulators; the clean "sirtuins are the longevity gene" narrative did not survive scrutiny intact.
What this means for taking a precursor
The honest position is narrower than the marketing and still worth something.
Well supported: sirtuins consume NAD+ stoichiometrically, and their activity is constrained by NAD+ availability. If NAD+ falls, sirtuin-dependent processes have less to work with.
Reasonably supported: precursor supplementation raises measured NAD+.
Not established: that doing so produces a change in a healthy adult that you would be able to detect in yourself. That link is the one the trials have not closed, and it is the one most product pages assert most confidently.
Keeping substrate available for a family of enzymes you depend on is a coherent reason to take a precursor. It is a mechanism-based bet, not a demonstrated outcome, and the difference is worth holding onto.
Related: Why NAD+ declines with age · CD38, the drain that grows · What to stack, and what not to