What is NAD+? A Cellular Energy Coenzyme Breakdown

Compound Spotlight

First, a correction that matters: NAD+ is not a peptide. It is a dinucleotide — a coenzyme built from two nucleotides rather than a chain of amino acids. It is grouped with research peptides commercially, not chemically, and understanding what it actually is explains most of the confusion around how it should be delivered.

Two jobs, not one

NAD+ is best known from metabolism diagrams as an electron carrier. In glycolysis, the citric acid cycle, and fatty acid oxidation it accepts electrons to become NADH, delivers them to the electron transport chain, and returns to NAD+. In this role it is not consumed — it cycles, and the NAD+/NADH ratio reflects the cell’s metabolic state.

The second role is different in kind. Three enzyme families use NAD+ as a substrate, cleaving it and consuming it permanently:

• Sirtuins — NAD+-dependent deacetylases that remove acetyl groups from histones and other proteins, influencing gene expression, mitochondrial biogenesis, and stress responses. Their activity is directly limited by NAD+ availability, which is the entire basis of the NAD+/longevity hypothesis.
• PARPs — poly(ADP-ribose) polymerases, activated by DNA damage. Extensive DNA damage causes heavy PARP activity, which can substantially deplete cellular NAD+.
• CD38 — an NAD+-consuming enzyme whose expression rises with age and inflammation. It is one of the better-documented mechanisms behind age-related NAD+ decline.

Because these enzymes destroy NAD+, the cell must continuously resynthesize it. That ongoing demand is what makes NAD+ availability a meaningful variable rather than a fixed background quantity.

The salvage pathway

Most NAD+ is not built from scratch. It is recycled through the salvage pathway, which recovers nicotinamide released by the consuming enzymes above. Nicotinamide phosphoribosyltransferase (NAMPT) converts nicotinamide to nicotinamide mononucleotide (NMN), and NMN adenylyltransferases then convert NMN to NAD+. NAMPT is the rate-limiting step, and its expression declines with age — a second documented contributor to falling NAD+, alongside rising CD38 consumption.

Nicotinamide riboside (NR) enters this pathway at a slightly different point, converted to NMN by nicotinamide riboside kinases.

The delivery problem

Here is the practical crux. NAD+ is a relatively large, negatively charged molecule. It does not readily cross the plasma membrane intact. Extracellular NAD+ is largely broken down by surface enzymes into smaller precursors — principally NMN and NR — which are then transported into the cell and reassembled into NAD+ internally.

The implication is straightforward and frequently glossed over: administering NAD+ directly is, to a substantial extent, an indirect way of delivering its precursors. This is precisely why the research literature is dominated by NR and NMN rather than NAD+ itself — they are smaller, they have identified transporters, and they enter the salvage pathway efficiently. Anyone comparing delivery routes should understand that the destination is the same intracellular pathway either way.

What the human evidence supports

The biochemistry above is settled science. The intervention question is not.

Human trials of NR and NMN have consistently shown that oral supplementation raises blood NAD+ levels — that part is reasonably well established. What remains far less clear is whether raising NAD+ produces meaningful functional or clinical benefits in healthy people. Trials have reported mixed results on outcomes such as insulin sensitivity, physical performance, and markers of aging, with several well-conducted studies finding no significant benefit despite confirming the biochemical change. The gap between “the marker moved” and “the person is better off” has not been closed.

It is also worth noting the regulatory position on NMN in the United States has been contested, with the FDA taking the view that it is excluded from marketing as a dietary supplement following its investigation as a drug candidate.

Frequently asked questions

Is NAD+ a peptide?

No. It is a dinucleotide coenzyme, chemically unrelated to peptides. It is grouped with research peptides by commercial convention only.

Why do sirtuins matter in this story?

Sirtuins require NAD+ as a consumed substrate, so their activity is limited by how much NAD+ is available. That dependency is the mechanistic basis for the proposed link between NAD+ levels and aging biology.

Why are NR and NMN studied more than NAD+ itself?

Because cells cannot efficiently import intact NAD+. The precursors are smaller, have known transporters, and feed directly into the salvage pathway that builds NAD+ inside the cell.

How do I know what is actually in the vial?

Every lot we sell has a published Certificate of Analysis from an independent, third-party lab confirming identity and purity. Lot numbers on the vial should match the COA you are referencing.

References

• Verdin E. NAD+ in aging, metabolism, and neurodegeneration. Science. 2015;350(6265):1208–1213.
• Camacho-Pereira J, et al. CD38 dictates age-related NAD decline and mitochondrial dysfunction through an SIRT3-dependent mechanism. Cell Metab. 2016;23(6):1127–1139.
• Rajman L, Chwalek K, Sinclair DA. Therapeutic potential of NAD-boosting molecules: the in vivo evidence. Cell Metab. 2018;27(3):529–547.
• Bogan KL, Brenner C. Nicotinic acid, nicotinamide, and nicotinamide riboside. Annu Rev Nutr. 2008;28:115–130.

View the NAD+ product listing →

Read our 5-Amino-1MQ breakdown →

Look up your lot Certificate of Analysis →

For laboratory and research use only. Not for human consumption. This article summarizes published research for informational purposes and is not medical advice, nor a recommendation or protocol for use.

Related research compounds

Arc Peptides supplies these compounds, each third-party tested for purity and identity with a lot-specific Certificate of Analysis:

• NAD+

For laboratory research use only. Not for human consumption.