How NAD+ works as both a redox coenzyme and a consumed substrate for sirtuins, PARPs and CD38, what the evidence on age-related decline actually shows, and practical notes on using and storing NAD+ in the lab.
Nicotinamide adenine dinucleotide (NAD+) is a coenzyme found in every living cell. It has two distinct jobs: it carries electrons in the redox reactions that fuel energy metabolism, and it is consumed as a substrate by signaling enzymes including the sirtuins, the poly(ADP-ribose) polymerases (PARPs) and CD38 [1][5]. Interest in NAD+ grew sharply once studies in several model organisms linked falling NAD+ levels to features of aging [3][5]. This guide explains the biochemistry, looks carefully at what the age-related decline data do and do not show, and covers the practical questions that come up when NAD+ is used in cell and biochemical work.
NAD+ is a dinucleotide: an adenine nucleotide and a nicotinamide nucleotide joined through their phosphate groups. The nicotinamide ring is the business end. In its oxidized form (NAD+) it accepts a hydride to become NADH, and this reversible redox cycling moves electrons through glycolysis, the citric acid cycle and fatty acid oxidation, delivering them to Complex I of the electron transport chain for oxidative phosphorylation [1][4]. The NAD+/NADH ratio therefore reflects a cell's metabolic state.
The second role is different in kind. Sirtuins, PARPs and CD38 cleave NAD+ itself, releasing nicotinamide [3][5]. Used this way, NAD+ is not recycled by redox chemistry; it has to be rebuilt. Cells do this mainly through salvage pathways that recycle nicotinamide via the enzyme NAMPT, and they can also use precursors such as nicotinamide mononucleotide (NMN) and nicotinamide riboside (NR) [2][3]. The size of the NAD+ pool at any moment is the balance between this synthesis and consumption.
The seven mammalian sirtuins (SIRT1-7) are NAD+-dependent deacylases that link metabolic state to gene regulation and stress responses [3]. SIRT1 regulates the transcriptional coactivator PGC-1alpha, a driver of mitochondrial biogenesis, and SIRT3 controls acetylation of mitochondrial proteins [4]. Because they require NAD+ as a co-substrate, their activity is sensitive to NAD+ availability [3].
PARP1 and PARP2 use NAD+ to build poly(ADP-ribose) chains at sites of DNA damage, recruiting repair machinery [5]. Heavy DNA damage can activate PARPs strongly enough to deplete cellular NAD+, which is why DNA repair and other NAD+-dependent processes are often described as competing for the same pool [4]. In human skin samples, PARP activity rose with age in males and correlated inversely with tissue NAD+ [7].
CD38 is an NAD+-degrading enzyme (NADase) that also generates calcium-mobilizing messengers such as cyclic ADP-ribose. In mice, CD38 expression and activity increased with age, and CD38 was required for the age-related fall in NAD+ and the accompanying mitochondrial dysfunction, acting at least in part through SIRT3 [9]. The same study identified CD38 as the main enzyme degrading the precursor NMN in vivo [9], which matters for anyone interpreting precursor experiments.
In rodents, a decline in tissue NAD+ with age has been reported across multiple tissues [5][6]. Human data are fewer but point the same way in the tissues studied:
The skin study's authors proposed a specific explanation: oxidative DNA damage accumulates with age, PARP is activated to repair it, and that activity consumes NAD+ [7]. The CD38 work in mice offers a second, not mutually exclusive route through increased NADase activity [9]. Which consumer dominates probably differs by tissue and by condition, and distinguishing them requires measuring the enzymes as well as NAD+ itself.
A careful 2020 review from the Baur laboratory adds necessary caution. It notes that human data remain limited, that apparent decline could reflect increased consumption, decreased synthesis or simply changes in the cell composition of aging tissues, and that better tools are needed to resolve NAD+ in specific cell types and subcellular compartments [6]. The same review points out that the threshold at which lower NAD+ actually causes physiological consequences is not known for most tissues [6]. Broad statements about how much NAD+ "everyone" loses by a given age go beyond what the evidence supports.
In animal studies, raising NAD+ with precursors such as NMN and NR has improved mitochondrial function and a range of metabolic and age-related measures [2][4][5]. How far these findings carry over to people is still open. Reviewers note that it remains to be established how best to restore NAD+ during aging and whether doing so has beneficial effects in older humans, with trials of oral precursors expected to provide some of the first direct evidence [5][6]. Those are questions about precursor compounds in clinical research; they are separate from the laboratory use of NAD+ described here.
NAD+ is a large, charged molecule, and how extracellular NAD+ reaches the intracellular pool is still debated. Surface enzymes can break it and NMN down into smaller precursors. In human tumor cells exposed to the NAMPT inhibitor FK866, low micromolar extracellular NAD+, NMN or NR rescued cell viability, and the ectoenzyme CD73 enabled conversion of extracellular NMN to NR for uptake while CD38 impaired it [10]. A later study reached a different conclusion for NAD+ itself: rescue of NAD+-dependent DNA repair by added NAD+ or NMN did not depend on CD73, recombinant CD73 processed NMN only poorly and NAD+ not at all, and CD73-knockout cells still raised intracellular NAD+ when supplied with NAD+ [11].
The practical takeaway is that the cell line matters. CD38 and CD73 expression differ widely between cell types, so the same concentration of NAD+ in the medium can produce different intracellular effects. Measuring intracellular NAD+ directly, rather than assuming it rose, is the more reliable design.
Store dry NAD+ at -20 °C, sealed and protected from moisture, and let the container reach room temperature before opening. In solution, stability depends on the buffer and on temperature. A 2024 study that followed NAD+ and NADH for up to 43 days found both highly stable in Tris buffer, with faster degradation in sodium phosphate or HEPES, and showed that even a mild rise in temperature made a significant difference [12]. For routine work, prepare solutions fresh or freeze single-use aliquots, avoid alkaline conditions for NAD+, and choose the buffer deliberately rather than by habit.
Northbridge Research Labs sends every batch for independent third-party testing. The certificate for NAD+ lot NJ1001 (1000 mg, tested August 2026) reports 99.94% purity and is published on our COA page; certificates are posted online rather than printed in the box.
Note: NAD+ from Northbridge Research Labs is supplied for laboratory research use only. It is not a dietary supplement and is not for human or veterinary use. Human findings described here come from published studies and are not claims about this material.
Studied compound
NAD+ (Nicotinamide Adenine Dinucleotide)
The same material this research covers — 99%+ purity, independently tested, with the certificate for each batch published online.
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