NAD+: The Molecule Everyone Names and Almost Nobody Has Studied

Everything below reports findings from cell cultures, isolated tissue and animals. This material is for research use only, not for human or veterinary use.

Search the literature for NAD+ and something odd turns up. Paper after paper names it in the title. Almost none of them put the dinucleotide itself into the system.

They used precursors instead: nicotinamide riboside, nicotinamide mononucleotide, combinations with pterostilbene. The dinucleotide appears as an outcome measure, a number in a sample, rather than as the thing administered.

Exactly one published infusion study gave NAD+ directly [7]. What happened in those six hours explains why everyone else uses a precursor, and it is the most useful single result in this whole field. Human milligram-per-day figures from precursor papers sit outside this profile.

Chemical identity

Two nucleotides joined tail to tail through a pyrophosphate bridge. One carries nicotinamide, the other adenine.

Property	Value
Systematic name	Nicotinamide adenine dinucleotide
Common names	NAD+, nadide, coenzyme I, diphosphopyridine nucleotide
Molecular formula	C21H27N7O14P2
Average mass	663.4 g/mol
Monoisotopic mass	663.1091 Da
CAS number	53-84-9
PubChem CID	5892
InChIKey	BAWFJGJZGIEFAR-NNYOXOHSSA-N
Stereocentres	12
Net charge at pH 7	Anionic overall, with a quaternary pyridinium
Reduced form	NADH
Phosphorylated form	NADP+

Why the charge matters

The plus sign is not decoration. It marks a permanent positive charge on the nicotinamide ring nitrogen, present whatever the pH.

Two phosphate groups carry negative charges alongside it. The molecule is therefore a zwitterion with a formal net negative charge, weighing 663 daltons, with twelve stereocentres and no lipophilic character at all.

Nothing about that description suggests a molecule that crosses membranes. Passive diffusion is not available to it, and no transporter for the intact dinucleotide has been established as a reliable oral route.

The oxidised and reduced forms are different reagents

NAD+ and NADH are the two halves of one redox couple, and a certificate naming the wrong one is describing different chemistry.

The oxidised form accepts a hydride. The reduced form donates one. Their absorbance differs, which is what makes the couple the workhorse of enzyme assays: NADH absorbs at 340 nm and the oxidised form does not.

Phosphorylation at the adenosine 2-prime position gives NADP+, which serves biosynthetic reductions rather than catabolic oxidations. Cells hold the two pools at different redox ratios on purpose.

A lot sold as NAD+ that reads at 340 nm is contaminated with the reduced form. That check takes seconds.

What NAD+ does in a cell

Two distinct roles, and confusing them is the source of most loose claims in this area.

The redox role

As a hydride carrier the molecule is catalytic. It cycles between oxidised and reduced states thousands of times, and the cell neither gains nor loses any in the process.

Glycolysis, the citric acid cycle and fatty acid oxidation all feed electrons into this couple. Nothing is consumed, so nothing needs replacing.

The consumed role

A second group of enzymes cleaves the molecule and keeps a piece. Sirtuins, PARPs and CD38 all break the glycosidic bond, releasing nicotinamide and transferring the ADP-ribose portion elsewhere [1].

This is the role that creates demand. An enzyme that destroys its substrate to do its job forces continuous resynthesis, and the salvage pathway exists to meet that.

Rajman and colleagues review the consumers in detail [1]. Their argument for raising the pool rests on this second role, and it depends on synthesis failing to keep pace with consumption.

Salvage versus de novo

Cells can make the nicotinamide ring from tryptophan, or they can salvage nicotinamide, nicotinic acid, nicotinamide riboside or nicotinamide mononucleotide. The salvage path is shorter. That is why precursor papers dominate the later file [1][2] and [5].

Intact NAD+ is not on that short path as an oral reagent. It has to arrive whole, or it has to be cut and rebuilt. The infusion study says the cut wins [7].

The molecule almost nobody has studied directly

Grant and colleagues ran the only published infusion study (PMID 31572171).

The one infusion study

They infused NAD+ intravenously and then tracked plasma and urine [7].

For the first two hours, nothing happened. Plasma levels of the compound did not rise. Neither did nicotinamide, methylnicotinamide, ADP-ribose or nicotinamide mononucleotide. The authors describe their own result as surprising.

Their conclusion is direct: at that infusion rate NAD+ leaves the plasma rapidly and completely for at least two hours. Material going in continuously produced no measurable rise in the thing being dosed.

What the metabolite profile showed

The pattern that emerged after two hours identified the mechanism. Products were consistent with glycohydrolase and pyrophosphatase activity [7], meaning enzymes cleaving the glycosidic bond and the pyrophosphate bridge.

Both cuts destroy the molecule. Circulating material meets enzymes that dismantle it faster than an infusion can supply it.

Urinary excretion carried its own detail. The parent compound and methylnicotinamide appeared, and nicotinamide did not.

Why this is one pilot study

Seven participants, one infusion rate, no placebo arm. This is a pilot and the authors label it as such.

It is also the entire direct administration file for the dinucleotide itself. Every other indexed paper discussed below administered something else. Those human endpoints sit outside this profile.

Why the oral question is the wrong one

Given the infusion result, oral NAD+ faces a harder problem still.

Material taken by mouth meets the gut wall and liver before circulation, and the same hydrolytic enzymes operate there. The two-hour plasma silence during a continuous intravenous infusion sets an upper bound on what any oral route could achieve.

The field drew that conclusion years ago, which is why the later literature runs on precursors. Nicotinamide riboside and nicotinamide mononucleotide are smaller, and they enter the salvage pathway rather than needing to arrive intact.

This mirrors the glutathione situation exactly. There the gamma-glutamyl bond means only one enzyme cleaves the tripeptide, and that enzyme sits where an oral dose passes. Here two enzyme classes attack a charged dinucleotide in the bloodstream itself.

Indexed precursor papers

Fourteen years of controlled papers, almost all of them dosing something upstream.

Paper	Agent	What the paper is	Why it sits outside
Dellinger 2017 [2]	NR plus pterostilbene	Indexed precursor study	Human endpoints
Dollerup 2018 [4]	NR	Clamp study	Human endpoints
Martens 2018 [3]	NR	Crossover study	Human endpoints
Conze 2019 [5]	NR	Dose-ordered biomarker study	Human milligram figures
Elhassan 2019 [6]	NR	Muscle metabolome	Human endpoints
Grant 2019 [7]	Intact NAD+ infusion	Plasma and urine PK	Kept as cited PK
Yoshino 2021 [9]	NMN	Clamp study	Human endpoints
Brakedal 2022 [12]	NR	Brain spectroscopy	Human endpoints
Norheim 2024 [14]	NR	Airway inflammation	Human endpoints

Nicotinamide riboside

NR carries most of the weight. Conze and colleagues reported a clean, dose-ordered rise in whole-blood NAD+ [5]. Dellinger and colleagues found the same shape using NR with pterostilbene [2].

Those papers exist. Their milligram-per-day figures sit outside this profile.

Nicotinamide mononucleotide

NMN sits one step closer to the finished molecule. Pencina and colleagues gave a pharmaceutical-grade formulation and reported a dose-related rise in blood levels [13]. Little unmodified NMN appeared in urine.

Again, the human figures stay outside this profile. The chemistry lesson is that NMN enters salvage and does not have to arrive as the dinucleotide.

What precursor papers report

Across these papers one finding never fails. Give a precursor and measured NAD+ rises.

It rises in whole blood [5][2], in aged skeletal muscle [6], in the brain measured by phosphorus magnetic resonance spectroscopy [12], and in hospitalised patients whose levels had fallen [8].

Simic and colleagues supply a sharp version in acute kidney injury: the pool fell on placebo and rose under precursor treatment [8]. Combination with pterostilbene in that paper and in Dellinger [2] means the rise cannot be assigned to NR alone.

So the salvage pharmacology works. Something taken upstream reaches tissue and raises a metabolite that was falling. Whether that matters for a physiological endpoint is a separate question, and those endpoints sit outside this profile.

What those papers do not license

Raising the number and changing an outcome have turned out to be different achievements.

Insulin sensitivity and muscle

Dollerup and colleagues ran a clamp study on NR (PMID 29992272) [4]. Elhassan and colleagues raised the muscle pool and then found mitochondrial bioenergetics unchanged [6]. Yoshino and colleagues ran a clamp on NMN in a different population [9].

Those papers exist. Their human outcome numbers sit outside this profile. The laboratory lesson is that a raised pool does not automatically move the function the rationale points at [6].

Vascular and inflammatory readouts

Martens and colleagues tested chronic NR and went no further than suggesting future work on blood pressure and arterial stiffness [3]. Norheim and colleagues reported an airway-inflammation signal [14]. Brakedal and colleagues reported a variable brain-pool rise [12].

Three groups also noted inflammatory cytokines moving in papers that were not designed as anti-inflammatory tests [6][12] and [14]. That pattern is weaker than one experiment built to test it. It is still the most repeated accidental finding in the file.

Indexed signals outside this profile

Altay and colleagues used a four-component mixture that included nicotinamide riboside [10]. Both phases favoured the mixture. Neither says which of the four components did anything.

Combination products complicate attribution. Pterostilbene appears alongside NR in two of the papers above [2][8], and a sirtuin-linked partner paired with a precursor cannot be separated after the fact.

Cite those papers for the fact that a file exists. Do not import their human endpoints into a laboratory protocol.

Age and the pool in tissue papers

Every supplementation argument here rests on one premise: NAD+ declines with age, and restoring it helps. The first half now has tissue support, and it arrives with a complication.

What the muscle metabolome showed

Janssens and colleagues compared muscle metabolomes across young adults and three groups of older adults: exercise-trained, normally active, and physically impaired [11].

The coenzyme was among the metabolites most clearly lower in older participants. Impaired individuals were lower still. Exercise-trained older individuals had levels resembling those of the young.

NAD+ abundance correlated with average steps per day, and with mitochondrial and muscle function.

Cause or consequence

Read that finding carefully. A trained 70-year-old looks like a 25-year-old on this measure.

If activity level predicts the number that well, the decline may be tracking fitness rather than driving it. The design is cross-sectional, so it cannot separate the two, and the authors claim an association rather than a mechanism.

That possibility reframes the supplementation case. Restoring a marker that follows physical activity is a different proposition from restoring a depleted substrate. No paper in this set has separated them.

What consumes NAD+

CD38, PARPs and the sirtuins all cleave the molecule to function [1].

CD38 attracts the most attention because its expression rises with age in preclinical work, which would raise consumption as synthesis holds steady. PARP activity rises with DNA damage, drawing on the same pool.

Norheim and colleagues built their COPD paper on that reasoning, pairing DNA damage with loss of the metabolite as parallel features of ageing and disease [14]. Their exploratory analyses pointed at genomic integrity pathways and reduced epigenetic ageing, and they flag those as requiring confirmation.

The consumption argument remains largely preclinical. Human data establish that NAD+ can be raised, not that raising it corrects a specific deficit.

What the record does not establish

Direct NAD+ administration has one pilot study behind it, in seven people, without a control arm [7]. Any claim about giving this compound itself rests on that alone.

Nobody has compared the routes. No trial has tested infusion against an oral precursor with the same endpoint in the same population, so the choice of precursor rests on pharmacokinetic reasoning rather than comparison.

Dose remains unsettled in the precursor file. Papers clustered at one milligram-per-day band because those are the amounts tested [4][5]. Those figures sit outside this profile.

Combination products complicate attribution [2][8] and [10].

Long-term outcome data do not exist. Follow-up runs weeks to months, endpoints are biomarkers and intermediate measures, and no paper has reported a hard clinical outcome that this profile would use.

Verifying research material

NAD+ is hygroscopic, unstable in solution and easy to mislabel, which makes the certificate worth reading closely.

Identity and purity

Mass is 663.4 average and 663.1091 monoisotopic. Mass spectrometry separates NAD+ from NADH by two daltons plus the charge difference.

The faster identity check is spectroscopic. Both forms absorb at 260 nm from the adenine, and only the reduced form absorbs at 340 nm. A 340 nm reading on material sold as the oxidised form is measuring contamination. Name which form was weighed. A 340 nm signal on a lot labelled NAD+ is NADH in the vial, not a method error.

Purity by HPLC should report the reduced form and free nicotinamide as named impurities. Both arise on storage, and a single purity figure hides which one dominates.

Pyrophosphatase cleavage gives nicotinamide mononucleotide plus AMP. Glycohydrolase cleavage gives nicotinamide plus ADP-ribose. A method that only integrates the parent peak will miss both.

Storage

Solutions decompose, and the two forms fail under opposite conditions. NAD+ is more stable in acid and degrades in alkali, while NADH does the reverse.

Prepare fresh, keep cold, and avoid repeated freeze-thaw. The solid is hygroscopic enough that absorbed water biases every subsequent weighing in the same direction, so aliquot on receipt.

Store the solid at minus 20 degrees Celsius, dry and dark. Expect a pale solid. Yellowing indicates degradation and warrants a fresh 340 nm reading before use.

Storage guidance is a house recommendation. Analytical documentation is per-lot release testing.

Kimera publishes third-party certificates of analysis for every lot in its COA database. Laboratories source NAD+ as a redox cofactor and enzyme substrate, often alongside glutathione where a thiol pool is under study, or CoQ10 where the electron transport chain is. Related work appears in the redox and cofactors category.

Enzyme-assay use

The 340 nm couple is why this molecule is a bench reagent at all. Start a dehydrogenase assay on the oxidised form near zero at 340 nm. The rise is NADH. Material that already reads at 340 nm has stolen the baseline.

Keep the working buffer on the acid side of neutral for the oxidised form. Keep the reduced form on the alkaline side. Mixing those habits is how a stock dies overnight.

Water in the solid is not a side issue. A hygroscopic dinucleotide that has sat open on the bench is no longer 663.4 g/mol of reagent. Karl Fischer or at least a drying step belongs next to the purity figure.

Nicotinamide as a named impurity tells you the glycosidic bond has already broken. AMP or NMN tells you the pyrophosphate has broken. Those two failure modes are different enzymes and different storage stories [7].

Common questions about NAD+

Why do papers use precursors instead of the compound itself? Because a six-hour intravenous infusion produced no plasma rise for two hours, with a metabolite profile showing enzymatic cleavage at two separate bonds [7]. Precursors enter the salvage pathway instead of needing to arrive intact.

Does oral precursor work raise the measured pool? Yes, reliably, in the indexed precursor papers [5]. Their milligram-per-day figures sit outside this profile.

Does that translate into a physiological effect? Inconsistently. Indexed clamp and muscle papers exist [4][6] and [9]. Their human endpoints sit outside this profile.

Which papers found something besides the biomarker? NMN and NR papers in selected populations reported signals [9][12] and [14]. Cite them as a file, not as a protocol.

Do levels really fall with age? Human muscle data say lower in older adults, lowest in the physically impaired, and near-youthful in the exercise-trained [11]. Abundance tracks daily step count, so activity may explain much of it.

What is the difference between the oxidised form and NADH? One hydride. They are the two states of a redox couple, and only the reduced form absorbs at 340 nm.

Is the compound consumed or recycled? Both, by different enzymes. Redox cycling recycles it endlessly; sirtuins, PARPs and CD38 destroy it to work [1].

Summary of the evidence

Identity: nicotinamide adenine dinucleotide, C21H27N7O14P2, 663.4 g/mol, CAS 53-84-9. A charged dinucleotide with twelve stereocentres and no membrane permeability.

Direct administration: one pilot infusion. No plasma rise for two hours, with products indicating glycohydrolase and pyrophosphatase cleavage [7].

Precursor pharmacology: reliable and dose-ordered in indexed papers. Human milligram-per-day figures sit outside this profile.

Endpoints in those papers are mixed and sit outside this profile.

Ageing: lower in older muscle, lowest when physically impaired, near-youthful when exercise-trained, and correlated with step count [11]. Association, from a cross-sectional design.

Write the form on the tube. Oxidised and reduced lots are not interchangeable reagents.

Status: supplied for laboratory research use only.

References

1. Rajman L, Chwalek K, Sinclair DA. Therapeutic potential of NAD-boosting molecules: the in vivo evidence. Cell Metab. 2018;27(3):529-547. PMID 29514064. DOI
2. Dellinger RW, Santos SR, Morris M, et al. Repeat dose NRPT (nicotinamide riboside and pterostilbene) increases NAD levels in humans safely and sustainably: a randomized, double-blind, placebo-controlled study. NPJ Aging Mech Dis. 2017;3:17. PMID 29184669. DOI
3. Martens CR, Denman BA, Mazzo MR, et al. Chronic nicotinamide riboside supplementation is well-tolerated and elevates NAD in healthy middle-aged and older adults. Nat Commun. 2018;9(1):1286. PMID 29599478. DOI
4. Dollerup OL, Christensen B, Svart M, et al. A randomized placebo-controlled clinical trial of nicotinamide riboside in obese men: safety, insulin-sensitivity, and lipid-mobilizing effects. Am J Clin Nutr. 2018;108(2):343-353. PMID 29992272. DOI
5. Conze D, Brenner C, Kruger CL. Safety and metabolism of long-term administration of NIAGEN (nicotinamide riboside chloride) in a randomized, double-blind, placebo-controlled clinical trial of healthy overweight adults. Sci Rep. 2019;9(1):9772. PMID 31278280. DOI
6. Elhassan YS, Kluckova K, Fletcher RS, et al. Nicotinamide riboside augments the aged human skeletal muscle NAD metabolome and induces transcriptomic and anti-inflammatory signatures. Cell Rep. 2019;28(7):1717-1728.e6. PMID 31412242. DOI
7. Grant R, Berg J, Mestayer R, et al. A pilot study investigating changes in the human plasma and urine NAD+ metabolome during a 6 hour intravenous infusion of NAD. Front Aging Neurosci. 2019;11:257. PMID 31572171. DOI
8. Simic P, Vela Parada XF, Parikh SM, et al. Nicotinamide riboside with pterostilbene (NRPT) increases NAD in patients with acute kidney injury (AKI): a randomized, double-blind, placebo-controlled, stepwise safety study of escalating doses of NRPT in patients with AKI. BMC Nephrol. 2020;21(1):342. PMID 32791973. DOI
9. Yoshino M, Yoshino J, Kayser BD, et al. Nicotinamide mononucleotide increases muscle insulin sensitivity in prediabetic women. Science. 2021;372(6547):1224-1229. PMID 33888596. DOI
10. Altay O, Arif M, Li X, et al. Combined metabolic activators accelerates recovery in mild-to-moderate COVID-19. Adv Sci (Weinh). 2021;8(17):e2101222. PMID 34180141. DOI
11. Janssens GE, Grevendonk L, Perez RZ, et al. Healthy aging and muscle function are positively associated with NAD abundance in humans. Nat Aging. 2022;2(3):254-263. PMID 37118369. DOI
12. Brakedal B, Dölle C, Riemer F, et al. The NADPARK study: a randomized phase I trial of nicotinamide riboside supplementation in Parkinson’s disease. Cell Metab. 2022;34(3):396-407.e6. PMID 35235774. DOI
13. Pencina KM, Lavu S, Dos Santos M, et al. MIB-626, an oral formulation of a microcrystalline unique polymorph of beta-nicotinamide mononucleotide, increases circulating nicotinamide adenine dinucleotide and its metabolome in middle-aged and older adults. J Gerontol A Biol Sci Med Sci. 2023;78(1):90-96. PMID 35182418. DOI
14. Norheim KL, Ben Ezra M, Heckenbach I, et al. Effect of nicotinamide riboside on airway inflammation in COPD: a randomized, placebo-controlled trial. Nat Aging. 2024;4(12):1772-1781. PMID 39548320. DOI

NAD+ is sold for laboratory research use only. Not for human consumption, nor medical, veterinary, or household uses.

Literature retrieved from PubMed.