NAD+ stands for nicotinamide adenine dinucleotide. It is a naturally occurring coenzyme that helps cells carry out essential chemical reactions, including reactions involved in energy metabolism. NAD+ also supplies enzymes involved in DNA-damage responses and other aspects of cellular regulation. 1 Health Professional Fact Sheet

Understanding NAD+ starts with separating three questions: what the molecule does inside cells, how researchers study it, and what human trials actually demonstrate. Its established biological importance does not automatically validate every claim made about NAD+ products.

Is NAD+ a peptide?

NAD+ is a coenzyme rather than a peptide. Its structure contains two linked nucleotide components, one associated with adenine and the other with nicotinamide. Peptides are chains of amino acids connected by peptide bonds. These are different chemical categories. 2 CID 10897651 – PubChem

The distinction matters because compounds discussed together in a research catalog can have very different structures and functions. For an introduction to peptide chemistry, see our guide to what peptides are.

The plus sign in NAD+ identifies its oxidized form. Its related reduced form is called NADH. The two forms work together in many metabolic reactions. 2

What does NAD+ do in cells?

Energy metabolism and mitochondrial function

NAD+ accepts electrons during certain metabolic reactions and becomes NADH. NADH can then donate electrons, including to the mitochondrial electron-transport chain, helping drive the production of ATP.

ATP provides immediately usable energy for many cellular processes. NAD+ and NADH help transfer electrons through the reactions that make that energy available. This cycle connects NAD biology with the breakdown of nutrients and mitochondrial function. 3 npj Metabolic Health and Disease

Researchers also study other molecules connected with mitochondrial biology. Our article on MOTS-c research and metabolism explores a separate research area; NAD+ and MOTS-c have different molecular identities and roles.

DNA-damage responses and cellular regulation

Some enzymes consume NAD+ as a substrate. These include members of the PARP family, which participate in DNA-damage responses, and sirtuins, which influence protein modification, metabolism, and gene regulation.

NAD+ availability is therefore connected to both energy-related chemistry and cellular signaling. However, supplying a molecule used by a repair pathway does not by itself demonstrate that a particular product repairs DNA or slows aging in people. 4 Nature Reviews Molecular Cell Biology

How does the body make NAD+?

The body can produce NAD using nutrients and recycled molecular components. Dietary niacin, also called vitamin B3, provides important building blocks. Some of the amino acid tryptophan can also be converted into NAD. 1

Cells also recycle nicotinamide through a process commonly called the salvage pathway. NR, or nicotinamide riboside, and NMN, or nicotinamide mononucleotide, are related molecules involved in NAD synthesis.

NAD metabolism is dynamic: cells continually make, use, and replenish it. A study using isotope tracing in cells and mice found substantial differences in NAD synthesis and turnover between tissues. That helps explain why a single concentration measurement cannot describe every aspect of NAD metabolism. 5 Health Professional Fact Sheet

NAD+ vs. NADH, NR, and NMN

These names appear together frequently, but they refer to different molecules.

Term	Full name or description	Relationship to NAD+
NAD+	Oxidized nicotinamide adenine dinucleotide	Accepts electrons in redox reactions and serves as a substrate for certain enzymes.
NADH	Reduced nicotinamide adenine dinucleotide	Carries electrons that can be passed to other reactions.
NR	Nicotinamide riboside	A precursor that can contribute to NAD synthesis.
NMN	Nicotinamide mononucleotide	An intermediate in pathways that produce NAD+.

The relationship between these molecules explains why researchers study NAD precursors. It also explains why results from an NR or NMN trial cannot automatically be attributed to NAD+ itself. The compound, route of administration, and tissue being measured all matter. 3 5 npj Metabolic Health and Disease

Why is NAD+ studied in aging research?

NAD metabolism is connected with processes that change during aging, including mitochondrial function, cellular stress responses, and the activity of NAD-consuming enzymes. These connections make it an important subject for laboratory and clinical investigation. 4

One often-cited human study examined 49 skin samples spanning a broad age range. Researchers found an association between increasing age and lower NAD+ concentrations in the tissue examined. Several other measured relationships differed between males and females. 6 PLOS One

That result needs its context. It was an observational study of skin samples, rather than an experiment showing that an intervention reversed aging. It also cannot establish a universal percentage decline throughout the entire body at a particular age.

A useful question for any aging-related claim is: Which tissue was measured, in which population, and did the study assess a meaningful health outcome? A change in a laboratory marker and an improvement in health are different findings.

What do human studies show?

Human research includes trials of NAD precursors and smaller investigations of direct NAD+ administration. The table below summarizes selected studies; each result applies to the intervention and population actually studied.

Study	What researchers investigated	Main finding and limitation
Martens et al., 2018	Oral NR in healthy middle-aged and older adults; 24 participants completed a crossover trial with six-week treatment periods.	NAD+ increased in sampled blood immune cells. The study did not establish longer life or equivalent changes in every organ. 7
Elhassan et al., 2019	Oral NR in 12 older men during 21-day treatment periods.	Several NAD-related metabolites in muscle changed, but measured mitochondrial bioenergetics did not improve. An altered NAD metabolome is broader than an increase in NAD+ itself. 8
Yoshino et al., 2021	Oral NMN for 10 weeks in 25 postmenopausal women with prediabetes and overweight or obesity.	Muscle insulin sensitivity improved. This specific finding does not establish diabetes prevention, general weight loss, or benefits from administering NAD+ itself. 9
Brakedal et al., 2026	Oral NR versus placebo for 52 weeks in 410 people randomized with early Parkinson disease.	NR did not improve clinical outcomes; the primary symptom outcome favored placebo. This trial does not support NR as a disease-modifying treatment for Parkinson disease. 10

These findings come from the original trial publications and the NIH’s account of the NMN investigation. nature.com

Together, these studies show why the outcome matters. Researchers may demonstrate that a compound changes NAD-related chemistry without demonstrating the hoped-for functional benefit. Other studies may find a benefit for a particular measurement in a narrowly defined population.

Evaluating the actual intervention, comparator, duration, and measured outcome is more informative than describing all of these findings as “NAD+ benefits.”

What about NAD+ infusions and injections?

Direct NAD+ administration is a separate research question from oral NR or NMN.

A 2019 pilot study examined blood and urine metabolites during and after intravenous NAD+ administration. It involved 11 men: eight receiving NAD+ and three receiving saline. The investigation helped describe how NAD-related compounds changed following administration.

Its size and design did not establish that NAD+ infusions improve everyday energy, reverse aging, or produce broad clinical benefits. It also did not establish long-term safety. 11 PubMed

Preparation quality is another separate issue. The FDA has warned about compounders using food-grade NAD+ to prepare intravenous products and described adverse-event reports consistent with excessive endotoxin exposure. A material’s identity or chemical purity alone does not establish suitability for injection. 13 FDA

How is NAD+ measured in laboratory research?

Researchers may measure NAD+, NADH, related metabolites, or the activity of enzymes that use them. The appropriate method depends on the question being investigated.

Sample preparation matters. In an analytical study, researchers showed that NAD-related redox cofactors can change between oxidized and reduced forms during extraction. Such changes can distort the ratio a researcher is trying to measure. The work compared preparation methods and used liquid chromatography–mass spectrometry to assess the compounds. 12 PMC

This is why a useful research report should identify the sample type, analytical method, handling conditions, and exact measurement. “NAD increased” is incomplete without knowing whether the measurement came from blood, a particular tissue, or a group of related metabolites.

Documentation also needs to match the material. Our guides to HPLC vs. LC-MS testing and how to read a certificate of analysis explain analytical concepts in the context of peptides. NAD+ requires methods and specifications appropriate to NAD+.

For any research material, distinguish the questions a test answers: identity, amount, chemical purity, and microbiological quality are separate characteristics. A reported result should be interpreted within the scope of the method used.

Frequently asked questions

Is NAD+ the same as vitamin B3?

Vitamin B3 provides precursors the body can use to make NAD. NAD+ is the resulting coenzyme form used in cellular reactions; the terms do not identify the same molecule. 1

Does more NAD+ automatically mean more energy?

A higher NAD-related measurement does not automatically demonstrate more ATP production, improved mitochondrial function, or a noticeable change in energy. In the Elhassan trial, muscle NAD-related metabolites changed without an improvement in measured mitochondrial bioenergetics. 8

Has NAD+ been proven to reverse human aging?

The studies discussed here do not establish that administering NAD+ or taking its precursors reverses human aging or extends human lifespan. Evidence about cellular mechanisms, biochemical markers, and specific clinical outcomes answers narrower questions. 4 7

Explore more educational articles in the Peptides Exchange Research Library.

This article is for scientific education. It does not provide dosing, administration, or treatment guidance. Laboratory research materials are not intended for human or animal use.

Sources

1. National Institutes of Health, Office of Dietary Supplements. Niacin: Fact Sheet for Health Professionals.
2. National Library of Medicine, PubChem. Beta-nicotinamide adenine dinucleotide, CID 10897651.
3. The role of NAD+ metabolism and its modulation of mitochondria in aging and disease. npj Metabolic Health and Disease, 2025.
4. Covarrubias AJ, et al. NAD+ metabolism and its roles in cellular processes during ageing. Nature Reviews Molecular Cell Biology, 2021.
5. Liu L, et al. Quantitative Analysis of NAD Synthesis-Breakdown Fluxes. Cell Metabolism, 2018.
6. Massudi H, et al. Age-Associated Changes in Oxidative Stress and NAD+ Metabolism in Human Tissue. PLOS ONE, 2012.
7. Martens CR, et al. Chronic nicotinamide riboside supplementation is well-tolerated and elevates NAD+ in healthy middle-aged and older adults. Nature Communications, 2018.
8. Elhassan YS, et al. Nicotinamide Riboside Augments the Aged Human Skeletal Muscle NAD+ Metabolome and Induces Transcriptomic and Anti-inflammatory Signatures. Cell Reports, 2019.
9. Yoshino M, et al. Nicotinamide mononucleotide increases muscle insulin sensitivity in prediabetic women. Science, 2021.
10. Brakedal B, et al. Nicotinamide Riboside for Patients With Early-Stage Parkinson Disease: The NOPARK Randomized Clinical Trial. JAMA, published October 8, 2026.
11. Grant R, et al. A Pilot Study Investigating Changes in the Human Plasma and Urine NAD+ Metabolome During a 6 Hour Intravenous Infusion of NAD+. Frontiers in Aging Neuroscience, 2019.
12. Lu W, et al. Extraction and Quantitation of Nicotinamide Adenine Dinucleotide Redox Cofactors. Antioxidants & Redox Signaling, 2018.
13. U.S. Food and Drug Administration. FDA reminds compounders to use ingredients suitable for sterile compounding.