NAD+ 1000mg

NAD+ is not a peptide. Nicotinamide adenine dinucleotide is a dinucleotide coenzyme of 663.43 g/mol, built from two nucleotides joined tail to tail through a pyrophosphate bridge: nicotinamide mononucleotide on one side, adenosine monophosphate on the other. It contains no amino acids and no peptide bonds, and it is not synthesised on a peptide synthesiser. It sits in a peptide catalogue because ageing biology treats it as a shared currency that the peptide audience also studies, not because the chemistry is related.

The molecule does two unrelated jobs, and confusing them is the source of most of the incorrect information written about it. The first is redox: NAD+ accepts a hydride ion and becomes NADH, then hands it back, cycling millions of times without being consumed. The second is signalling: sirtuins, poly(ADP-ribose) polymerases, CD38 and SARM1 cleave the glycosidic bond between nicotinamide and the ribose and destroy the molecule to do their work. The second job is why NAD+ has a turnover rate at all, and why it can run short.

Tissue NAD+ falls with age in every mammal that has been measured, and restoring it in old animals reverses several markers of mitochondrial decline. What is genuinely contested is how to restore it. Intact NAD+ is a large, doubly charged dinucleotide that crosses the plasma membrane poorly, and the evidence that it is degraded outside the cell before anything gets in is strong. That is why the precursors nicotinamide riboside and nicotinamide mononucleotide dominate the published literature, and why the human trials of those precursors, including the ones that moved nothing, are the honest place to look for what NAD+ repletion does and does not do.

In its redox role NAD+ is a hydride carrier. The C4 position of the nicotinamide ring accepts a hydride ion, two electrons and one proton, from a substrate; the remaining proton is released to solution, which is why the reduced species is written NADH plus H+. The standard reduction potential of the NAD+/NADH couple is about minus 0.32 V, which places it near the electron-donating end of the respiratory chain and makes it the entry point for electrons from glycolysis, beta-oxidation and the citric acid cycle. Hundreds of dehydrogenases depend on it. Crucially, this cycling consumes nothing: a single NAD+ molecule can be reduced and reoxidised indefinitely, so redox chemistry alone would never create a demand for new synthesis.

The demand comes from the second class of reactions, in which NAD+ is a substrate rather than a cofactor. Sirtuins SIRT1 through SIRT7 remove acyl groups from lysine residues and, in doing so, cleave NAD+ into nicotinamide and 2'-O-acyl-ADP-ribose. PARP1 and PARP2 build poly(ADP-ribose) chains onto proteins at sites of DNA damage, consuming one NAD+ per ADP-ribose unit added. CD38 hydrolyses NAD+ mainly to ADP-ribose, with cyclic ADP-ribose as a minor product. SARM1, the executioner of axon degeneration, carries a TIR domain that Essuman and colleagues showed in 2017 has intrinsic NADase activity, cleaving NAD+ into ADP-ribose, cyclic ADP-ribose and nicotinamide. Every one of these enzymes destroys the molecule, and every one of them releases nicotinamide, which is a feedback inhibitor of sirtuins and of SARM1.

Because the pool is consumed, it has to be resupplied, and three routes do that. The salvage pathway is the dominant one: nicotinamide phosphoribosyltransferase (NAMPT) condenses nicotinamide with 5-phosphoribosyl-1-pyrophosphate to give NMN, and nicotinamide mononucleotide adenylyltransferase (NMNAT1 in the nucleus, NMNAT2 in the cytosol and Golgi, NMNAT3 in mitochondria) adenylylates NMN to NAD+. NAMPT is the rate-limiting step. The Preiss-Handler route starts from nicotinic acid through NAPRT and finishes with NAD synthetase. The de novo route runs from tryptophan through the kynurenine pathway to quinolinic acid and QPRT. Isotope tracing by Liu and colleagues in 2018 showed that in mice the de novo route from tryptophan operates essentially only in the liver, which then exports nicotinamide for the rest of the body to salvage, and that NAD+ flux varies by more than an order of magnitude between tissues, high in small intestine and spleen, low in skeletal muscle.

A peptide is a chain of amino acids joined by amide bonds between an alpha-carboxyl and an alpha-amino group. NAD+ has neither amino acids nor amide backbone bonds. It is a dinucleotide: two ribose sugars, each carrying a base, joined through a diphosphate. One base is nicotinamide, the amide of pyridine-3-carboxylic acid and the form of vitamin B3 that mammals recycle. The other is adenine, the same base found in ATP and in DNA. The nicotinamide sits on a positively charged quaternary nitrogen, which is where the plus sign in NAD+ comes from, and that formal charge is on the ring nitrogen, not on the molecule as a whole.

The distinction is not pedantry. It determines handling. Peptides are cleaved by proteases and are usually stable across a moderate pH range; NAD+ is not touched by proteases at all but is hydrolysed at its glycosidic bond by a whole family of NAD glycohydrolases, and it is chemically labile in alkali. It determines analysis: a peptide is characterised by sequence confirmation and by HPLC against a synthetic standard, whereas NAD+ purity is judged against its own well-defined ultraviolet spectrum and against known degradation products such as nicotinamide and ADP-ribose. It also determines what a molar concentration means. A 1,000 mg vial of NAD+ is about 1.51 mmol, which is a very large number of moles compared with a 10 mg vial of a 3 kDa peptide.

A cofactor that only cycles has no metabolic price. If NAD+ did nothing but shuttle hydride between dehydrogenases, a cell would synthesise its pool once and never think about it again. What makes NAD+ interesting to ageing research is that four families of enzymes spend it: sirtuins, PARPs, the CD38 and CD157 ADP-ribosyl cyclases, and SARM1. Each cleaves the nicotinamide-ribose bond and returns free nicotinamide, so each imposes a resynthesis cost that NAMPT has to meet.

This is what turns NAD+ into a shared budget that different processes compete for. DNA damage activates PARP1, which draws on the pool; a fall in the pool reduces sirtuin activity, because sirtuin Km values for NAD+ are close to ambient concentration rather than far below it; reduced SIRT1 and SIRT3 activity in turn affects mitochondrial function and the acetylation state of hundreds of substrates. Camacho-Pereira and colleagues connected the last link explicitly, showing that CD38-driven NAD+ decline produces mitochondrial dysfunction through a SIRT3-dependent mechanism.

Isotope tracing has put numbers on the competition. Liu and colleagues measured NAD+ synthesis and breakdown fluxes rather than concentrations, and found that in cell lines NAD+ was made from nicotinamide and consumed largely by PARPs and sirtuins, while in vivo flux varied by more than an order of magnitude across tissues. Concentration alone is a poor readout of a molecule whose whole significance is turnover, which is a recurring problem when a study reports that a treatment raised NAD+ but says nothing about which consumer got the extra supply.

The decline itself is well documented. Massudi and colleagues measured NAD+ in human pelvic skin from 49 donors aged from newborn to 77 and found a strong negative correlation with age in both sexes (p = 0.001, r = -0.706 in males; p = 0.01, r = -0.537 in females), alongside rising DNA damage and rising PARP activity that correlated inversely with tissue NAD+. SIRT1 activity fell with age in males. The pattern replicates across rodent tissues and appears in human muscle and brain in later work.

Two mechanisms have the best evidence, and they are not exclusive. The first is increased consumption. CD38 expression and activity rise with age; CD38 knockout mice are protected from the decline; and pharmacological CD38 inhibition with 78c reversed tissue NAD+ decline in aged mice and improved glucose tolerance, muscle function and cardiac performance. The second is chronic PARP activation by accumulating DNA damage, which is what the human skin correlations point at.

A third contributor is diversion rather than destruction. Nicotinamide N-methyltransferase methylates nicotinamide to 1-methylnicotinamide using S-adenosylmethionine, and mammals have no enzyme that reverses that methylation. Every methylated nicotinamide is one that NAMPT will never salvage. NNMT expression rises in white adipose tissue in obesity, which is the rationale behind the NNMT inhibitor 5-Amino-1MQ stocked in this catalogue and the reason it is discussed on the same page as NAD+ despite being an unrelated small molecule.

This is the central unresolved question for anyone comparing NAD+ with its precursors, and most product literature does not raise it at all. Intact NAD+ is large by small-molecule standards at 663.43 g/mol, carries multiple negative charges on its pyrophosphate at physiological pH, and has no known plasma membrane transporter in mammals. Passive diffusion across a lipid bilayer is not a plausible route for a molecule with those properties.

The direct experimental work points the other way. Nikiforov and colleagues targeted PARP activity into the mitochondrial matrix as a live reporter of organellar NAD+ and mapped which extracellular precursors actually reach the inside of human cells. Their conclusion was that besides nicotinamide and nicotinic acid, only the corresponding nucleosides readily enter cells, and that nucleotides including NAD+ and NMN undergo extracellular degradation to permeable precursors first. The enzymes that do this are on the cell surface: CD38 and the ENPP family hydrolyse NAD+, and CD73, the ecto-5'-nucleotidase, dephosphorylates NMN to nicotinamide riboside. Ratajczak and colleagues then showed with stable isotope labelling that NMN is metabolised extracellularly to NR before uptake, and that nicotinamide riboside kinase 1 is necessary and rate-limiting for the use of both.

Human infusion data are consistent with that picture. Grant and colleagues infused NAD+ intravenously at 3 micromoles per minute over six hours and found no change in plasma NAD+ or in its metabolites for the first two hours, which they interpreted as the infused NAD+ being rapidly and completely removed from plasma. The metabolite profile they did eventually see, including ADP-ribose and methylnicotinamide, matched NAD+ glycohydrolase and pyrophosphatase activity rather than intact distribution.

None of this means extracellular NAD+ is inert. Degradation products are precursors, and a molecule that is cleaved to NMN, then to NR, then taken up and rephosphorylated has still delivered its nicotinamide moiety. What it does mean is that the mechanistic claim implied by the phrase direct NAD+ supply, that the intact dinucleotide crosses into the cytosol, is not what the transport literature supports.

In January 2019 Grozio and colleagues reported in Nature Metabolism that the Slc12a8 gene encodes a specific NMN transporter. They found Slc12a8 highly expressed and NAD+-regulated in the murine small intestine, reported that knockdown abolished NMN uptake in vitro and in vivo, that transport was sodium-dependent and specific for NMN rather than NR, that Slc12a8 deficiency lowered NAD+ in jejunum and ileum, and that expression rose in the aged ileum. If correct, it would mean at least one NAD+-pathway nucleotide can enter a cell without being dephosphorylated first.

In July of the same year Schmidt and Brenner published a formal comment titled Absence of evidence that Slc12a8 encodes a nicotinamide mononucleotide transporter, arguing that the reported data did not exclude extracellular conversion of NMN to NR ahead of uptake and questioning the transport kinetics. Grozio and colleagues replied in the same issue. The exchange has not been settled by an independent replication that the field treats as decisive, and the original paper also carries a published erratum.

The practical consequence is that a page claiming NMN enters cells through a dedicated transporter, and a page claiming NMN must be dephosphorylated by CD73 first, are both describing a live scientific disagreement rather than a settled fact. Anyone designing an uptake experiment should treat the transporter as a hypothesis to be tested in their own system, not as background.

The honest summary is that raising NAD+ in humans is easy and moving downstream endpoints is not. Martens and colleagues showed NR at 1 g daily raised NAD+ in peripheral blood mononuclear cells by about 60 percent over 6 weeks in 30 randomised healthy middle-aged and older adults, with good tolerability and only a suggestion of blood pressure and arterial stiffness effects. Elhassan and colleagues confirmed the biochemistry in tissue: 1 g of NR daily for 21 days in 12 aged men raised the skeletal muscle NAD+ metabolome and lowered circulating inflammatory cytokines, but muscle mitochondrial bioenergetics did not change, and the muscle transcriptome moved in the opposite direction to the one predicted, with downregulation of energy metabolism and mitochondrial pathways.

Two well-powered metabolic trials found nothing. Dollerup and colleagues randomised 40 obese, insulin-resistant men aged 40 to 70 to NR at 2 g daily or placebo for 12 weeks and measured insulin sensitivity with a hyperinsulinaemic-euglycaemic clamp, substrate metabolism by indirect calorimetry with labelled glucose and palmitate, body composition by DXA and MRI, and liver fat by MR spectroscopy. Insulin sensitivity, endogenous glucose production, glucose disposal and oxidation, resting energy expenditure, lipolysis, lipid oxidation and body composition were all unchanged. Remie and colleagues gave 13 healthy overweight or obese men and women NR at 1 g daily for 6 weeks in a crossover design with muscle biopsies and clamps. Muscle NAD+ metabolites rose and muscle acetylcarnitine rose from about 3,025 to about 4,558 pmol per mg dry weight, fat-free mass rose about 1.3 percentage points and sleeping metabolic rate rose, but insulin sensitivity, mitochondrial function, hepatic and intramyocellular lipid, cardiac energy status and ejection fraction, ambulatory blood pressure and inflammatory markers were all unchanged.

The clearest positive human result used NMN rather than NR and a population selected for metabolic impairment: Yoshino and colleagues found increased insulin-stimulated glucose disposal and increased muscle AKT and mTOR phosphorylation in 25 prediabetic postmenopausal women given NMN at 250 mg daily for 10 weeks. That trial drew published commentary in Science, Cell Metabolism and Cardiovascular Research within months, which is a fair indication of how contested this area is.

For intravenous NAD+ specifically, the human dataset is thin and mostly about tolerability. Reyna and colleagues reported a retrospective review from a commercial wellness setting in 2026 comparing four consecutive daily infusions of 500 mg NAD+ against 500 mg NR. The NAD+ group reported moderate to severe gastrointestinal symptoms, raised heart rate and chest pressure during infusions, and needed longer infusions to get through them, averaging 97 minutes against 37 minutes for NR. All symptoms resolved when the infusion ended. ALT, AST, hsCRP, BUN and creatinine and TSH did not change in either group over 30 days.

The four compounds attack the same pool from different points, and the differences are chemical, not marketing. NAD+ is the finished molecule at 663.43 g/mol, the one the enzymes actually use, and the one least able to cross a membrane. NMN is one adenylylation step away at 334.22 g/mol, and the literature indicates it is dephosphorylated by CD73 to NR before entry in most cell types. NR is the nucleoside at 255.25 g/mol, uncharged, and it is the species that equilibrative nucleoside transporters handle and that NRK1 phosphorylates on the inside, which is why Ratajczak and colleagues found NRK1 to be rate-limiting for both NR and NMN.

5-Amino-1MQ is not in that pathway at all. It is a synthetic methylquinolinium cation of 159.21 g/mol that inhibits nicotinamide N-methyltransferase, and it raises NAD+ by closing a drain rather than by adding supply: nicotinamide that is not methylated to 1-methylnicotinamide stays available for NAMPT to salvage. In differentiated 3T3-L1 adipocytes it raised intracellular NAD+ roughly 1.2 to 1.6 fold. That is a smaller multiple than a precursor can produce, but it is achieved without loading the extracellular space with nucleotides, and it is tissue-biased towards adipose because that is where NNMT expression is highest. It has no human trial data at all, which is the opposite balance of evidence to NR.

The comparison that matters experimentally is therefore not which one is best but which question is being asked. A study of NAD+-dependent enzyme kinetics in a cell-free or permeabilised system wants the intact dinucleotide, because that is the substrate. A study of whole-cell NAD+ repletion in intact cells has to reckon with the extracellular degradation route, and a precursor removes that confound. A study of the methylation drain wants an NNMT inhibitor, because no amount of precursor addresses a sink.

NAD+ has a well-defined ultraviolet signature and this is what identity and purity work is built on. Both oxidised and reduced forms absorb near 259 nm through the adenine ring. Reduction adds a second band at 340 nm with an extinction coefficient of 6,220 M-1 cm-1, so the ratio of absorbance at 260 nm to 340 nm distinguishes NAD+ from NADH directly, and any NADH contamination in a nominally oxidised preparation is visible without chromatography. Reversed-phase HPLC with ultraviolet detection separates NAD+ cleanly from its common degradation products, nicotinamide and ADP-ribose, and mass spectrometry confirms the 663 mass.

The stability behaviour is the mirror image of NADH and has been understood since Lowry, Passonneau and Rock characterised the pyridine nucleotides in 1961. Oxidised NAD+ is comparatively stable in acid and degrades in alkali; reduced NADH is stable in alkali and degrades in acid. A buffer chosen for one form is the wrong buffer for the other, and a solution left at neutral to slightly alkaline pH at room temperature will lose oxidised NAD+ measurably over hours to days. Solutions should be prepared fresh, kept cold and kept out of light.

The lyophilised free acid is hygroscopic. Ambient moisture pulled into an opened vial both dilutes the mass being weighed and accelerates hydrolysis, so vials are best equilibrated to room temperature before opening to avoid condensing water onto cold powder. Repeated freeze and thaw cycles are the other common cause of quiet degradation in stored aliquots, and single-use aliquoting removes that variable. None of this is peptide handling advice repurposed: the failure modes are different because the chemistry is different.

It does not establish that the age-related fall in NAD+ is a cause of ageing rather than a consequence of the DNA damage and inflammation that accompany it. The interventional rodent data are suggestive because raising NAD+ reverses specific mitochondrial phenotypes, but the human interventional data have so far shown that the biochemistry can be moved without the physiology following.

It does not establish that intact extracellular NAD+ enters cells in mammals. No plasma membrane NAD+ transporter has been identified, the mapped route runs through extracellular hydrolysis to permeable precursors, and the one human infusion study that looked found the infused molecule cleared from plasma before it accumulated.

It does not establish a durable clinical benefit for any NAD+ precursor in a healthy population. Two randomised metabolic trials with hard endpoints, clamps, biopsies and imaging returned null results for insulin sensitivity and mitochondrial function. The single clearly positive insulin sensitivity result came from a small trial in a metabolically impaired group and has not been replicated at scale.

And it does not establish a safety profile for intravenous NAD+ beyond short-term tolerability in a retrospective commercial cohort. There is also an unresolved theoretical question about NAD+ availability in tissues carrying occult malignancy, since several tumour types are dependent on NAD+ biosynthesis, which is exactly why NAMPT inhibitors have been investigated as anticancer agents.