asxan.ai Agents Hub

NAD+

Evidence Fact Sheet

The NAD+ precursor family covers five molecules — NMN, NR, niacinamide, niacin, and NADH — that share one biological goal (raising cellular NAD+) while differing sharply in human evidence base, dose, side-effect profile, and regulatory status across the United States, the European Union, China, and Brazil. This educational hub maps the comparative evidence honestly: where head-to-head human trials exist (almost none), where each precursor is strongest (niacinamide for skin via the ONTRAC NEJM trial, NMN for older-adult walking speed and amateur aerobic capacity, NR for the broadest RCT count, NADH for chronic fatigue research, niacin for legacy lipid research with modern caveats), why direct oral and intravenous NAD+ are weakly supported, and where claims have outrun the data. Educational only — not medical advice and not a substitute for clinical judgement.

Quick Orientation

Five molecules share one goal — raising cellular NAD+ — but diverge sharply in route, dose, and human evidence; blood NAD+ rising to ~2x baseline is not the same as a clinical benefit.

Five molecules are commonly grouped under the heading "NAD+ boosters". Each works by feeding the cellular NAD+ pool, but the routes, doses, and human evidence differ sharply. This family page is the comparative orientation for the dedicated sub-pages: NMN, NR, NMNH (reduced NMN, emerging research compound), and NADH (the reduced cofactor form). Niacin and niacinamide are vitamin B3 forms with their own long histories in public-health and dermatology research; they are referenced here in the comparative tables and in the goal-by-goal sections.

A note on regulatory status before you read on: the snapshot card above shows family-level chips representing the vitamin-B3 members (niacinamide and niacin), which are the only members compliant across all four markets covered here (US, EU, China, Brazil). The other precursors diverge sharply — NMN is under a full-chain prohibition in Brazil and is not approved in China, NR is still under EU Novel Food evaluation, and NADH/NMNH lack clear approval pathways in several markets. See the Regulatory Snapshot below for the full per-member breakdown; the four-market chips must not be read as applying to every precursor.

Three statements anchor everything below. First, NAD+ concentrations decline with age across multiple human tissues — roughly 40 to 60 percent from young adulthood to the seventies, observed independently by Harvard, Washington University, and the University of Helsinki research groups, and reviewed across the field. Second, oral NAD+ precursors at clinical doses raise blood NAD+ to approximately twice baseline in multiple randomised controlled trials. Third, blood NAD+ elevation is not the same as a clinical benefit, and the strength of evidence for downstream endpoints varies by precursor and by goal.

Direct NAD+ vs the precursor route — three questions in sixty seconds

Does swallowing intact NAD+ work? As of 2026, there is no large double-blind randomised controlled trial demonstrating that oral intact NAD+ raises blood NAD+ in humans more reliably than its precursors do. The reason is mechanical and biochemical, not ideological: NAD+ is a 663-dalton dinucleotide with two phosphate groups; it is partially hydrolysed in stomach acid (which sits at pH 1–2), cleaved by intestinal NADase enzymes into smaller fragments (NR, NMN, niacinamide) before enterocyte absorption, and further degraded in hepatic first-pass metabolism. The molecule that arrives in peripheral blood is not the molecule that was swallowed.

What about intravenous NAD+? A PubMed search for double-blind randomised controlled trials of intravenous NAD+ in humans returns no large studies for any indication as of 2026-05-26. The historical literature includes 1960s-era case reports and small open-label cohorts, often combined with B vitamins, minerals, and glutathione in functional-medicine clinic protocols. The FDA, EFSA, and ANVISA have not approved intravenous NAD+ infusion for any clinical indication. This is not a statement that intravenous NAD+ is harmful; it is a statement that the evidence base for routine clinical decision-making is currently thin.

Is age-related NAD+ decline real, and what should I do about it? NAD+ decline with age is a robust finding across multiple human tissues — skin (50-year-old skin NAD+ at approximately half the 20-year-old level), skeletal muscle (30 to 50 percent reduction in adults over 70), and brain. The defensible response is precursor supplementation (NR, NMN) that re-enters the salvage pathway and reconstitutes the dinucleotide pool, or NADH supplementation that directly delivers reduced cofactor to mitochondrial Complex I. Direct intact NAD+ supplementation is not the evidence-supported route.

Member Comparison Table

The table below summarises the family on a common set of dimensions, including the direct-oral and intravenous NAD+ strategies. Each cell is referenced to a sub-page or to a citation in the References section.

Compound / strategy Pathway / mechanism Strongest single piece of human evidence Typical studied dose Notable caveat
NMN (β-nicotinamide mononucleotide) Salvage pathway via NRK1/NRK2 and NMNAT Multi-centre dose-finding RCT (Yi 2022/2023, PMID 36482258, n=80) and chronobiology RCT (Kim 2022, PMID 35215405, afternoon dosing in older adults) 250–1000 mg/day; up to 1250 mg/day for 4 weeks validated for safety (Fukamizu 2022) Long-term (>6 months) human safety data are sparse. Brazil prohibition (ANVISA RE 1139/2022) blocks all NMN supply.
NR (nicotinamide riboside) Salvage pathway via NRK1/NRK2 Trammell 2016 PK landmark (PMID 27721479) and Brakedal 2022 NADPARK Parkinson brain-NAD+ (PMID 35235780) 300–1000 mg/day; up to 3000 mg/day short term (NR-SAFE 2023) A 2020 Dollerup trial in insulin-resistant obese men reported no skeletal-muscle benefit — an honest negative result.
Niacinamide (nicotinamide, vitamin B3 amide) Direct entry into the salvage pool ONTRAC NEJM phase-three RCT (Chen 2015, PMID 26488693, n=386, 23% reduction in non-melanoma skin cancer) 500 mg twice daily (skin); 500–1000 mg/day general High doses may inhibit sirtuins; interaction with carbamazepine is theoretical.
Niacin (nicotinic acid, vitamin B3 acid) Preiss-Handler pathway Historical CDP-era HDL data; AIM-HIGH 2011 and HPS2-THRIVE 2014 NEJM negative on statin background; Ferrell 2024 4PY signal 1–3 g/day for lipid effect (prescription range) Flushing in >80% of users; modern post-statin lipid programmes question the risk-benefit at therapeutic doses.
NADH (reduced cofactor) Direct mitochondrial Complex I electron donor (not a precursor) Forsyth 1999 chronic fatigue RCT (PMID 10071523, n=26) and Birkmayer 2002 jet-lag cognition RCT (PMID 12385067) 5–20 mg/day enteric-coated Sample sizes are small; never independently compared head-to-head with the precursor strategies.
Direct oral NAD+ Intended to deliver the intact dinucleotide 0 large double-blind RCTs of intact oral NAD+ n/a — marketed "NAD+" capsules typically contain precursors 663-dalton polar molecule; degraded by gastric acid and intestinal NADase before absorption.
Intravenous NAD+ Bypasses the gut; intent is to elevate plasma NAD+ 0 large double-blind RCTs; largest cohorts under n=30, open-label 250–1000 mg per session in functional-medicine protocols Sample sizes under 30, combination protocols, no regulator approval.

The Underlying Biology — Why the Precursors Differ

NMN and NR feed the salvage pathway, niacin uses the separate Preiss-Handler route, and NADH is not a precursor at all but the reduced cofactor — treating them as one homogeneous group obscures this distinction.

NAD+ is a small molecule (nicotinamide adenine dinucleotide, molecular weight 663 daltons) that sits at the centre of cellular energy metabolism, DNA-damage repair signalling, and the activity of the sirtuin family of NAD+-dependent deacetylases. Three classes of cellular consumer draw down the NAD+ pool: sirtuins (acting on histones and metabolic regulators), the PARP family of DNA-repair enzymes, and CD38, an ecto-enzyme whose activity climbs with age and chronic inflammation.

The salvage pathway is the dominant route by which mammalian cells regenerate NAD+. In simplified form, intracellular nicotinamide is phosphoribosylated by NAMPT to NMN, which is then adenylated by the NMNAT isoforms (NMNAT1 in the nucleus, NMNAT2 in the Golgi and cytoplasm, NMNAT3 in mitochondria) to NAD+. NAMPT expression declines with age in several tissues — this is the kinetic step that the salvage-feeding precursors target. NMN and NR both feed directly into this loop, NR via dephosphorylation and rephosphorylation through NRK1/NRK2, NMN via either direct transport or intestinal dephosphorylation to NR followed by re-entry. The SLC12A8 NMN transporter hypothesis (Grozio 2019 Nature Metabolism) remains contested after Schmidt and Brenner's 2020 non-replication, and consumer-facing writing should treat it as a hypothesis rather than an established route.

Niacinamide enters the salvage pool directly. Niacin enters via the Preiss-Handler pathway, which uses a different enzymatic chain (NAPRT, NMNAT, NADS) and is a key reason niacin's metabolic behaviour differs from the others — including the cutaneous flushing response that affects more than 80 percent of users at therapeutic lipid-modifying doses. NADH is structurally not a precursor at all but the reduced electron-carrier form that donates electrons directly at mitochondrial Complex I. Treating "NAD+ precursors" and NADH as one homogeneous group obscures this distinction.

The Bioavailability Problem in Detail — Why Direct Oral NAD+ Is Poorly Absorbed

The intact 663-dalton NAD+ dinucleotide is poorly orally absorbed — degraded by stomach acid and intestinal NADase into NR/NMN/niacinamide fragments before it reaches the blood, which is why the evidence-supported route is precursors, not direct NAD+.

  • 663 DaNAD+ molecular weight
  • 0large double-blind RCTs of oral intact NAD+
  • 3 stagesgastric · intestinal · hepatic degradation

NAD+ (nicotinamide adenine dinucleotide, oxidised form, PubChem CID 5893) is a dinucleotide of nicotinamide and adenine linked through two ribose sugars and two phosphate groups. The molecular formula is C21H27N7O14P2 and the molecular weight is 663.43 g/mol. Two physicochemical properties matter for oral supplementation:

High polarity. The two phosphate groups make NAD+ highly water-soluble and poorly lipid-soluble. Cell membranes are phospholipid bilayers; crossing one requires either an active transporter or local hydrolysis-then-resynthesis. Mammalian cells do not have a dedicated NAD+ uptake transporter that is well characterised at plasma-membrane level for the intact dinucleotide. The main intracellular route is via smaller fragments — NR enters via ENT/CNT nucleoside transporters and is rephosphorylated to NMN by NRK1 (PMID 27725675), and then to NAD+ by NMNAT.

Chemical instability. NAD+ at stomach pH (1–2) undergoes spontaneous hydrolysis, with the thermodynamics favouring decomposition to NMN and AMP. The integrity of an "NAD+ capsule" depends on enteric coating, gastric residence time, and post-absorption stability — and even with the best engineering, the molecule does not arrive in peripheral blood unchanged.

Three sequential degradation steps explain why oral intact NAD+ is poorly absorbed:

Stage Location What happens to intact NAD+
1 · Gastric hydrolysis Stomach, pH 1–2 Spontaneous decomposition to NMN + AMP fragments.
2 · Intestinal NADase cleavage Small intestine and colon NAD+ is enzymatically cleaved by NADase enzymes (CD38, CD157/BST1) into NR, NMN, and niacinamide.
3 · Hepatic first-pass metabolism Liver Even fragments that survive the small intestine encounter further degradation by hepatic NADase before reaching the peripheral circulation.

The honest summary: the peripheral blood concentration of intact NAD+ after oral dosing is poorly characterised by human pharmacokinetic data. Compare with the human pharmacokinetics of NR (Trammell 2016 PMID 27721479) and NMN (Irie 2020 PMID 31685720; Yi 2022 PMID 36482258), both of which have multiple human PK studies demonstrating measurable elevation of blood NAD+ metabolome from oral dosing.

Intravenous NAD+ — What the Data Actually Look Like

Despite clinic marketing, PubMed contains zero large double-blind RCTs of intravenous NAD+ for any indication; the largest studies are open-label cohorts under n=30, usually confounded by combination protocols.

  • 0large double-blind IV NAD+ RCTs
  • ~n=30largest IV NAD+ study size

What is often said in functional-medicine settings. Functional-medicine clinics frequently market intravenous NAD+ infusions at 250 to 1000 mg over 4 to 8 hours per session, often as a course of multiple sessions, for indications including general healthy ageing, post-substance-use recovery, and chronic fatigue. Costs are typically in the range of several hundred to a few thousand US dollars per protocol. The marketing rationale is that intravenous administration bypasses the oral bioavailability problem.

What PubMed actually contains. A 2026-05-26 PubMed search for "intravenous NAD+ infusion humans" restricted to randomised clinical trials returns zero large double-blind RCTs. The published intravenous NAD+ human literature consists of: historical case reports from the 1960s and 1970s (OHollaren and others) that do not meet modern randomised-trial standards; small pharmacokinetic studies with sample sizes under 10; and small open-label observational cohorts under 30 participants, frequently in substance-use-disorder settings, with intravenous NAD+ administered in combination with B vitamins, minerals, and glutathione. The FDA, EFSA, and ANVISA have not approved intravenous NAD+ for any clinical indication.

Three caveats apply to the existing intravenous NAD+ studies. Sample-size ceiling: the largest published intravenous NAD+ clinical studies have around n=30, are open-label, and would not qualify as A- or B-tier evidence under the GRADE framework. Combination-protocol confound: most functional-medicine clinic protocols combine intravenous NAD+ with B vitamins, minerals, and glutathione, so attribution to NAD+ specifically is statistically unfeasible in this design. Pharmacokinetic gap: the actual intracellular NAD+ elevation in human tissue biopsies after intravenous NAD+ infusion is not well characterised. Plasma NAD+ elevation does not equal tissue NAD+ reconstitution — CD38 and other NADases continue to consume NAD+ at peripheral and tissue levels.

Where Each Precursor Is Strongest — A Goal-by-Goal Walk

This section ties the family into the goal-level longevity stack, cognitive support, athletic performance, skin beauty, and heart health pages, and into the lifestyle-level senior 60+, athletic performance lifestyle, and high-stress lifestyle pages.

Skin — Niacinamide (Grade A)

RCT supported

Niacinamide is the only cluster member with a phase-three NEJM randomised trial: ONTRAC cut non-melanoma skin cancer by 23% in a high-risk population.

  • 23%NMSC relative reduction (ONTRAC)
  • n=386ONTRAC phase-3 RCT
  • 11%actinic keratosis reduction

For skin endpoints, niacinamide is the only cluster member with a phase-three randomised controlled trial published in the New England Journal of Medicine. The ONTRAC trial (Chen AC, Martin AJ, Choy B, et al. 2015 NEJM, PMID 26488693, n=386) reported a 23 percent relative reduction in non-melanoma skin cancer at 500 mg twice daily for 12 months in a population at high prior-cancer risk, and an 11 percent reduction in actinic keratosis. Allen 2023 NEJM extended the framework into the post-transplant immunosuppressed population. Bissett 2005 (Dermatologic Surgery) reported improvements in wrinkles, hyperpigmentation, and elasticity with topical-plus-oral niacinamide. NMN, NR, and NADH carry no comparable human skin trial.

For the skin beauty goal and the senior 60+ lifestyle, niacinamide is the cluster member to read first.

Walking speed, grip strength, sleep, sit-to-stand in older adults — NMN (Grade B)

RCT supported

Three independent randomised trials in older adults underwrite the NMN signal for walking speed, grip strength, and sleep, with afternoon dosing reproducibly outperforming morning.

  • 3 RCTsindependent older-adult trials
  • 250 mg/dayNMN studied dose
  • p=0.033walking-speed improvement

Three independent randomised trials in older Japanese adults underwrite the NMN signal in this domain. Igarashi 2022 (PMID 35927255, n=42 older men, 250 mg/day for 12 weeks) reported improved walking speed (p=0.033) and left-hand grip strength (p=0.019). Kim 2022 (PMID 35215405, n=108, 250 mg/day for 12 weeks, morning vs afternoon arms) reported that the afternoon-dosing arm — but not the morning arm — improved five-times sit-to-stand, sleep quality, and self-reported fatigue. Morita 2024 reproduced the chronobiology pattern (afternoon > morning) in 60 older adults. The afternoon-versus-morning dosing finding is one of the more reproducible timing signals in the supplement literature.

For the longevity stack goal and the senior 60+ lifestyle, NMN is the cluster member with the densest human evidence.

Amateur aerobic capacity — NMN (Grade B)

RCT supported

In 48 amateur runners, NMN produced dose-dependent aerobic-capacity gains across 300, 600, and 1200 mg/day — the cluster's strongest single athletic-performance trial.

  • n=48amateur runners (Liao 2021)
  • 300–1200 mg/daydose-dependent range

Liao 2021 (PMID 34238308) in 48 amateur runners reported dose-dependent improvements in aerobic capacity at 300, 600, and 1200 mg/day across six weeks. This is the strongest single trial for an athletic-performance endpoint in the cluster. NR carries a separate cardiopulmonary-exercise signal — Bock 2024 in Nature Communications (PMID 38871717) showed a six-minute walk-test improvement in peripheral artery disease patients — but this is a peripheral vascular-disease cohort, not athletes. NADH has a strong mechanistic case (Complex I electron donor) but no randomised athletic-performance trial.

For the athletic performance goal and the athletic performance lifestyle, NMN is the cluster member to consider first; NADH carries mechanistic adjacency only. One additional consideration in competitive contexts: intravenous NAD+ infusion may be viewed by some sport governance bodies as a metabolic modulator and could carry compliance risk during competition season — athletes should consult their sport-specific anti-doping authority for current guidance.

Cognitive support — Mixed; honest framing essential

Emerging

Cognition is the weakest evidence sector across the cluster — NR raised brain NAD+ in Parkinson's but motor gains were exploratory only; the defensible framing is 'neuroprotective biomarker support', not 'improves memory'.

  • n=20NR in MCI (Vreones 2024)
  • n=26NADH Alzheimer pilot (Demarin 2004)

The NADPARK trial (Brakedal 2022 Cell Metabolism, PMID 35235780) showed that NR raised brain NAD+ in Parkinson's disease patients. Motor improvements were exploratory, not confirmed primary endpoints. Vreones 2024 GeroScience (PMID 37994989, n=20) reported sub-domain cognitive improvements in mild cognitive impairment on NR. Niacinamide improved retinal-layer function in glaucoma patients in a crossover trial (Hui 2020, PMID 32212232). NADH carries Demarin 2004 (PMID 15134388, n=26 Alzheimer's, small positive RCT) and Birkmayer 2002 (PMID 12385067, n=35 jet-lag cognition, positive). The defensible framing across the cluster is "neuroprotective biomarker support" — not "improves memory" or "treats Alzheimer's disease".

For the cognitive support goal, the high-stress lifestyle, and senior populations, this is the weakest evidence sector across the cluster and the one most prone to over-claiming in third-party marketing.

Cardiometabolic — Niacin is a cautionary tale

Emerging

No precursor has positive cardiovascular hard-endpoint evidence at supplement doses; niacin specifically is a cautionary story — modern post-statin trials showed no added benefit and Ferrell 2024 flagged its 4PY metabolite as pro-inflammatory.

  • >80%niacin flushing rate
  • 0precursors with positive CV hard-endpoint data

Niacin at therapeutic lipid-modifying doses (1 to 3 grams per day) was the dominant pre-statin HDL-raising agent — Cochrane review work by Schandelmaier et al. 2017 (PMID 28617537) summarises that era. The modern post-statin trials AIM-HIGH 2011 (NEJM PMID 22085343) and HPS2-THRIVE 2014 (NEJM PMID 25014686) showed no added cardiovascular-event benefit when niacin was layered on top of statin therapy, and HPS2-THRIVE in particular reported increased serious adverse events. Ferrell M et al. 2024 in Nature Medicine (PMID 38383798) identified the niacin metabolite 4PY as a promoter of vascular inflammation correlating with major adverse cardiovascular events, a mechanistic warning at high doses. NMN and NR cardiometabolic data are early — Katayoshi 2023 NMN (PMID 36797393) showed a non-significant trend toward reduced arterial stiffness, and the Bock 2024 NICE trial (PMID 38871717) in peripheral artery disease reported a six-minute walk-test improvement on NR. No precursor in this cluster has positive cardiovascular hard-endpoint evidence at supplement doses.

For the heart health goal, the honest cluster message is "evidence is currently soft and niacin specifically is a cautionary story" — read alongside the medical guideline above.

Regulatory Snapshot — United States · European Union · China · Brazil

Regulatory status is the most divergent dimension in the family — niacinamide and niacin are authorised vitamins everywhere, NMN swings from US-legal to Brazil-prohibited, and NADH/NMNH sit in regulatory voids.

This educational hub covers four regulatory markets in line with the asxan.ai international scope: the United States (FDA), the European Union (EFSA), China (NMPA), and Brazil (ANVISA). National regulatory frameworks outside these four are not covered on this hub. The snapshot chip row above represents the vitamin-B3 members (niacinamide and niacin), which are the only members compliant across all four markets; the per-member divergences are shown in full below and must not be read off the family-level chips.

Compound United States · FDA / DSHEA European Union · EFSA China · NMPA Brazil · ANVISA
NMN Legal dietary supplement following 2025-09-29 FDA withdrawal of the 2022 IND exclusion. NDI framework applies. Novel Food evaluation pending across six applications (Uthever most advanced, public consultation completed Feb 2025). Not approved as a novel food or health-food raw material (NMPA filing rejected); cosmetic-topical use only. Full-chain prohibition under RE 1139/2022 (7 April 2022) — covers commercialisation, distribution, manufacture, import, advertising, and use, including cross-border e-commerce.
NR Niagen GRAS; long-standing structure-function claims under DSHEA. Novel Food status; national-level variation among member states. Not listed in the novel-food directory; cross-border e-commerce distribution only; a separate novel-food application is required. Case-by-case evaluation; not on the IN 28/2018 positive list.
Niacinamide GRAS as vitamin B3 amide form; standard vitamin labelling. Authorised vitamin form; six EFSA Article 13 nutrition claims at recommended daily intake levels (energy metabolism, nervous system, psychological function, skin, mucous membranes, reduction of fatigue). Established nutrient: GB 14880 food fortification and vitamin B3 function within the NMPA health-food framework. On the IN 28/2018 positive list for dietary supplements.
Niacin (acid form) GRAS at vitamin doses; sustained-release lipid-modifying products above 500 mg cross into the prescription category (Niaspan). Authorised vitamin form; safe upper intake limit of the acid form is 10 mg/day, which is far below the lipid-modifying clinical dose range. Established nutrient: GB 14880 food fortification and vitamin B3 function within the NMPA health-food framework. On the IN 28/2018 positive list; doses above 1 gram per day may trigger drug-regulatory oversight.
NADH Legal dietary supplement under DSHEA (Enada and equivalents marketed since the late 1990s). National-level acceptance varies (e.g. permitted as a supplement in Austria and Germany); zero EFSA-authorised health claims. No compliant sales pathway — not approved as a novel food or health-food raw material. No specific approval pathway; case-by-case evaluation.

Standard prohibited-claim language applies across all four jurisdictions. Disease claims (treats / cures / prevents Alzheimer disease, Parkinson disease, type 2 diabetes, cardiovascular disease, cancer, etc.) and lifespan claims ("extends lifespan", "reverses aging") are not permitted regardless of evidence base.

Safety — Cross-Cluster Summary

Across the whole family there is no adequate human safety data in pregnancy/lactation for the supplement-form precursors, and long-term (>6 month) data remain sparse for NMN and NR.

Detailed dose tables and contraindications are on each sub-page. The cross-cluster safety summary:

  • Pregnancy and lactation. No adequate human safety data for NMN, NR, NMNH, or NADH. Avoid the supplement-form precursors. Niacinamide and niacin have standard prenatal-vitamin guidance at recommended daily intake levels; supraphysiological dosing should not be self-initiated.
  • Children and adolescents. No adequate human safety data for the supplement-form precursors.
  • Active liver disease. Niacinamide and niacin should be approached cautiously; high-dose niacin is documented to cause hepatotoxicity (especially sustained-release formulations).
  • PARP inhibitors (oncology). Theoretical interaction across the cluster — NAD+ is the substrate for PARP. Oncology supervision is required.
  • Statin therapy. Niacin should not be self-added to a statin programme; the AIM-HIGH and HPS2-THRIVE trials showed no added benefit and increased adverse events.
  • Long-term human safety (beyond six months). Sparse for NMN and NR. Strongest long-term data are for niacinamide (12-month ONTRAC follow-up) and NADH (decades of commercial use under DSHEA).

Dedicated Sub-Pages

Niacinamide and niacin are referenced in this hub via the comparison table and the cardiometabolic and skin sections; dedicated sub-pages for niacinamide and niacin remain on the editorial roadmap.

Read the Evidence (deep dive long-form)

For deep-dive narrative across the NAD+-axis evidence base (25-year clinical chronology · NMN vs NR precursor decision · reduced NADH vs NMNH redox-form comparison), see the three dedicated evidence articles forming the NAD+-axis cluster:

The three evidence articles form the NAD+-axis evidence cluster, with explicit peer cross-links among them. Cross-reading all three alongside this hub builds the holistic NAD+-axis evidence picture from precursor chronology → decision framework → redox-form choice.

Where ASXAN's Research Focus Sits

ASXAN's research focus across longevity-relevant ingredient categories includes ingredient-level evidence aggregation across NAD+ precursor and reduced cofactor compounds, with the goal of supporting an internationally accessible, evidence-first educational reference. This NAD+ family hub is part of that reference and is editorial in nature; it does not promote any specific product, brand, or investment opportunity.

References

All PMIDs verified against PubMed. Effect sizes are reported as published.

  1. PMID 26488693 · Chen AC, Martin AJ, Choy B et al. 2015 · NEJM · ONTRAC niacinamide non-melanoma skin cancer phase-3 RCT.
  2. PMID 27721479 · Trammell SAJ et al. 2016 · Nat Commun · NR pharmacokinetics landmark.
  3. PMID 27725675 · Ratajczak J et al. 2016 · Nat Commun · NRK1 controls NMN/NR metabolism.
  4. PMID 35235780 · Brakedal B et al. 2022 · Cell Metab · NADPARK NR brain NAD+ in Parkinson disease.
  5. PMID 38871717 · Bock JM et al. 2024 · Nat Commun · NICE NR peripheral artery disease.
  6. PMID 37994989 · Vreones M et al. 2024 · GeroScience · NR in mild cognitive impairment.
  7. PMID 33888596 · Yoshino M et al. 2021 · Science · NMN postmenopausal RCT.
  8. PMID 36482258 · Yi L et al. 2022 · GeroScience · NMN dose-finding.
  9. PMID 36740954 · Pencina KM et al. 2023 · J Clin Endocrinol Metab · MIB-626.
  10. PMID 34238308 · Liao B et al. 2021 · NMN amateur runners, dose-dependent aerobic capacity.
  11. PMID 35927255 · Igarashi M et al. 2022 · npj Aging · NMN older adults.
  12. PMID 35215405 · Kim M et al. 2022 · Nutrients · NMN chronobiology.
  13. PMID 36797393 · Katayoshi T et al. 2023 · Sci Rep · NMN arterial stiffness trend.
  14. PMID 36002548 · Fukamizu Y et al. 2022 · Sci Rep · NMN safety 1250 mg/4wk.
  15. PMID 39116016 · Zhang J et al. 2025 · Crit Rev Food Sci Nutr · meta-analysis 12 NMN RCTs.
  16. PMID 10071523 · Forsyth LM et al. 1999 · NADH chronic fatigue RCT (n=26).
  17. PMID 12385067 · Birkmayer JGD et al. 2002 · NADH jet-lag cognition RCT.
  18. PMID 15134388 · Demarin V et al. 2004 · NADH Alzheimer's small positive RCT (n=26).
  19. PMID 25386668 · Castro-Marrero J et al. 2015 · Antioxid Redox Signal · CoQ10+NADH CFS.
  20. PMID 32212232 · Hui F et al. 2020 · niacinamide retinal function in glaucoma crossover trial.
  21. PMID 38383798 · Ferrell M et al. 2024 · Nat Med · niacin 4PY metabolite vascular-inflammation signal.
  22. PMID 22085343 · AIM-HIGH Investigators 2011 · NEJM · niacin on statin background, no added CV benefit.
  23. PMID 25014686 · HPS2-THRIVE Collaborative Group 2014 · NEJM · niacin on statin background.
  24. PMID 28617537 · Schandelmaier S et al. 2017 · Cochrane review of niacin cardiovascular outcomes.
  25. PMID 31685720 · Irie J et al. 2020 · NMN single-dose safety / PK.
  26. PMID 39326681 · NAD+ homeostasis and exercise adaptation review · 2024.
  27. PMID 39422945 · NAD+ Precursors for Alzheimer review · J Alzheimers Dis · 2024.

Tags

NAD+ · NMN · NR · Niacinamide · Niacin · NADH · salvage pathway · Preiss-Handler pathway · sirtuin · CD38 · longevity research · evidence-first.

Educational Disclaimer

This page is educational reference content and is not medical advice. It is not intended to diagnose, treat, cure, or prevent any disease. Discuss any supplement use, including any intravenous infusion protocol, with a qualified healthcare provider who is independent of any clinic selling the protocol, particularly if you are pregnant or breastfeeding, take prescription medication, have a diagnosed condition, or are undergoing oncology, cardiology, or endocrinology treatment. Regulatory status varies by jurisdiction; the four markets in scope here are the United States, the European Union, China, and Brazil.

Frequently Asked Questions

The questions below address the most commonly searched questions on the NAD+ precursor family across general web search and AI assistants. Answers reference the evidence cited throughout this page; they are intentionally concise and direct readers to the relevant page sections for deeper context.

1. What is the NAD+ precursor family, and which compounds does it cover?

The NAD+ precursor family covers five compounds that share one downstream goal — raising cellular NAD+ — but differ in absorption route, evidence base, dose, side-effect profile, and regulation: NMN (β-nicotinamide mononucleotide), NR (nicotinamide riboside), niacinamide (the amide form of vitamin B3, also called nicotinamide), niacin (the acid form of vitamin B3), and NADH (the reduced cofactor form).

2. Which NAD+ precursor has the strongest single piece of human evidence?

Niacinamide carries the single most rigorous trial: the ONTRAC phase-three randomised controlled trial published in the New England Journal of Medicine in 2015 (Chen et al., n=386), which reported a 23% relative reduction in non-melanoma skin cancer with 500 mg twice daily for 12 months in a high-risk population. No other NAD+ precursor has reached this evidentiary tier.

3. Is NMN better than NR?

No head-to-head randomised controlled trial in humans has compared NMN and NR on a clinical endpoint. The two precursors collapse to similar intracellular intermediates and both elevate blood NAD+ at typical doses. Claims of superiority either way are not supportable by the current human evidence.

4. If I buy a product labelled NAD+, am I actually swallowing NAD+?

In most cases no. The intact NAD+ dinucleotide (molecular weight 663 daltons) is poorly orally bioavailable: it is partially hydrolysed in stomach acid, cleaved by intestinal NADase enzymes into smaller fragments such as NR, NMN, and niacinamide, and further degraded in hepatic first-pass metabolism. Most "NAD+" products on the market are in fact NR, NMN, or niacinamide once you read the supplement-facts panel.

5. Why is direct oral NAD+ supplementation considered weakly supported?

The NAD+ dinucleotide is large (molecular weight 663 daltons), highly polar, and chemically unstable in stomach acid. It is largely degraded into smaller fragments (NR, NMN, niacinamide) before absorption, which then re-enter the salvage pathway. As of 2026 there is no large double-blind randomised controlled trial demonstrating that oral intact NAD+ raises blood NAD+ in humans more reliably than its precursors do.

6. Does intravenous NAD+ have strong human evidence?

No large double-blind randomised controlled trial of intravenous NAD+ is currently indexed in PubMed for any clinical indication. The frequently cited 1961 OHollaren report is a historical case series that does not meet modern randomised-trial standards. The FDA, EFSA, and ANVISA have not approved intravenous NAD+ for any clinical indication. Functional-medicine clinic protocols often combine NAD+ with B vitamins, minerals, and glutathione, which makes any single-component attribution difficult.

7. If direct NAD+ is poorly absorbed, why does anyone sell it?

Commercial branding often uses the word "NAD+" because it is the consumer-recognised end-state molecule. Read the supplement-facts panel: the actual active ingredient is typically NR, NMN, or niacinamide, which are precursors that re-enter the salvage pathway inside cells. The branding shortcut and the bioavailable molecule are not the same thing.

8. Should I do an intravenous NAD+ infusion at a functional-medicine clinic?

There is no large double-blind randomised controlled trial supporting routine clinical use of intravenous NAD+ infusion for any indication. If you are considering it, talk to a physician who is independent of the clinic selling the protocol. Do not treat user experience reports or testimonials as substitute for randomised evidence.

9. What is the role of NADH compared with the precursors?

NADH is the reduced electron-carrier form and is the molecule that directly donates electrons at mitochondrial Complex I. It is not a precursor — it is the operative cofactor that the precursors are ultimately trying to top up indirectly. Stabilised oral NADH has approximately 25 years of human safety data and modest randomised evidence in chronic fatigue syndrome (Forsyth 1999) and jet-lag cognition (Birkmayer 2002).

10. Does any NAD+ precursor extend human lifespan?

No. No randomised controlled trial of any NAD+ precursor has used lifespan as an endpoint, and no human study has demonstrated lifespan extension. Mouse lifespan studies exist but do not transfer onto human use. The defensible framing is that NAD+ precursors raise blood NAD+ and produce selected functional improvements in some populations.

11. Which precursor is most appropriate for healthy older adults?

For older adults the densest human evidence cluster is NMN at 250 mg/day, with three independent randomised trials (Igarashi 2022, Kim 2022, Morita 2024) showing functional improvements in walking speed, grip strength, and sleep. Two independent trials also report that afternoon dosing outperforms morning dosing for sleep and sit-to-stand outcomes in older adults — one of the more reproducible chronobiology findings in the supplement literature.

12. Why is niacin treated differently from the other precursors in this family?

Niacin enters NAD+ via the distinct Preiss-Handler pathway and causes cutaneous flushing in over 80% of users at therapeutic lipid-modifying doses (1 to 3 grams per day). The modern post-statin trials AIM-HIGH (2011 NEJM) and HPS2-THRIVE (2014 NEJM) did not show added cardiovascular benefit on top of statin therapy. Ferrell 2024 in Nature Medicine identified the niacin metabolite 4PY as a promoter of vascular inflammation. Niacin therefore sits in a different risk-benefit category from the other precursors and is not recommended for self-supplementation outside medical supervision.

13. Is the SLC12A8 NMN transporter mechanism settled science?

No. Grozio et al. 2019 in Nature Metabolism proposed SLC12A8 as a mammalian NMN transporter. Schmidt and Brenner 2020 in the same journal reported they could not reproduce the finding. The mechanism remains contested as of 2026. NMN absorption is more reasonably described as involving multiple proposed routes, including intestinal dephosphorylation to NR, and SLC12A8 should be referenced as a contested hypothesis rather than an established route.

14. What regulatory status do NAD+ precursors have in the United States, the European Union, China, and Brazil?

In the United States, niacinamide, niacin, NR (Niagen GRAS), and NADH are legal dietary supplements; NMN status was restored on 29 September 2025 when the FDA withdrew its 2022 IND exclusion determination. In the European Union, niacinamide and niacin are authorised vitamin forms (with EFSA Article 13 claims at recommended daily intake levels), NMN is under Novel Food evaluation (six applications pending), NR has Novel Food status with national variation, and NADH is permitted as a supplement in some member states with no central EFSA authorisation. In China, niacinamide and niacin are established nutrients (GB 14880 fortification plus vitamin B3 functions within the health-food framework under NMPA), NMN is not approved as a novel food or health-food raw material (the NMPA filing was rejected; cosmetic-topical use only), and NADH has no compliant sales pathway. In Brazil, niacinamide and niacin are listed on ANVISA IN 28/2018; NR and NADH require case-by-case evaluation, and NMN specifically is under a full-chain prohibition under ANVISA RE 1139/2022 of 7 April 2022.

15. Where should I start reading if I want one precursor that has the most consumer-relevant evidence per dollar?

Niacinamide. It carries the ONTRAC NEJM phase-three trial for non-melanoma skin cancer reduction at high-risk populations, has EFSA-authorised general nutrition claims at recommended daily intake levels, has a clean and well-characterised long-term safety record across decades of vitamin B3 research, and is by an order of magnitude the lowest-cost member of the family. The honest caveat is that niacinamide does not carry NMN-style human data for muscle, walking speed, sleep, or aerobic capacity.

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