[Memo] NR / NMN / NAD+: Research Update and Prime Lab’s Assessment

This is an Internal Research Memo from Prime Lab, documenting our ongoing review of this topic. It does not represent Prime Lab's final position. The memo will be updated as new research emerges.

Research Memo · 2026.10.14

Summary

• Oral NR or NMN reliably raises blood NAD+ to 1.5–3 times baseline. This has been demonstrated repeatedly. Yet, as of October 2026, no randomized controlled trial has shown an improvement in any health outcome in healthy people.

• The largest trial was negative.

  A 52-week trial of NR in early Parkinson's disease, involving 410 participants, did not slow disease progression. It is the largest and longest randomized trial in the NR/NMN field to date.

• Pooled findings for both muscle function and metabolism are null.

  Multiple meta-analyses found no improvement in older adults' grip strength, walking speed, or sit-to-stand performance, nor in fasting glucose, insulin, HbA1c, or blood lipids.

• Reports of “more energy” have not held up against placebo controls.

  Several small, manufacturer-funded NMN trials reported improvements in secondary fatigue or sleep outcomes, while most primary outcomes were negative. NR has no positive evidence on energy or cognitive outcomes. Placebo groups also improved.

• Population-level evidence concerns dietary niacin alone.

  Several US cohorts associate higher dietary niacin intake with lower mortality, but these are studies of diet, not supplements, with substantial confounding. There are no long-term cohorts of NR/NMN users.

• Claims that “human NAD+ declines with age” need to specify the tissue.

  Direct measurements provide evidence in skin, brain, and skeletal muscle; whole-blood NAD+ did not change with age across seven independent cohorts. Using a blood NAD+ test to assess aging is unsupported.

• Precursors do not simply enter cells as intact molecules.

  Isotope tracing shows that most oral NR/NMN is converted to nicotinamide and nicotinic acid before reaching tissues. Much of the rise in blood NAD+ proceeds through established synthesis pathways involving the gut microbiota and liver. NMN and NR raise blood NAD+ to a similar extent.

• The “activate sirtuins to extend lifespan” narrative rests on shaky foundations.

  Early assays of sirtuin activators produced artifacts, and lifespan extension from Sir2 overexpression could not be reproduced after standardizing genetic backgrounds. NAD+ is more likely to act through multiple pathways.

• Animal lifespan evidence is thinner than commonly assumed.

  NR did not extend mouse lifespan in the rigorous, multicenter Interventions Testing Program (ITP). Evidence that NMN extends lifespan comes only from a preprint that has not been peer reviewed.

• Safety: reassuring short-term tolerability, missing long-term evidence, and two signals to watch.

  Tolerability is good within 12 weeks; human data beyond one year are lacking. The terminal niacin metabolite 4PY is associated with cardiovascular events—an association, not proof of causation. NR promoted breast cancer metastasis to the brain in one mouse model, at doses far above supplement doses.

• Regulatory clearance addresses safety and classification, not efficacy.

  The FDA withdrew its drug-exclusion determination for NMN in 2025 because NMN had been marketed as a supplement before the investigational drug application; the decision was unrelated to efficacy. The EU's EFSA explicitly does not assess efficacy in this process. Japan uses a company notification system. China has still not approved NMN as a food ingredient.

• Prime Lab's assessment.

  Healthy people do not need NR/NMN for “anti-aging.” These are currently supplements with reasonably reassuring safety data and unproven efficacy, rather than established longevity interventions. Confirmatory trials in specific disease populations are worth following.

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I. Research Progress

1. Discovery and basic functions

The foundational history of NAD+ began more than a century ago. In 1906, Harden and Young identified a heat-stable “coenzyme” in yeast fermentation. In 1936, von Euler and Myrbäck identified its chemical structure; that same year, Warburg and Christian established its role as a hydrogen carrier in redox reactions. In 1948, Kornberg elucidated its biosynthesis. NAD+ accepts hydrogen during glycolysis, the tricarboxylic acid cycle, and fatty acid oxidation to form NADH, which then supports ATP production through mitochondrial oxidative phosphorylation. NAD+ is also a substrate for enzymes including sirtuins, PARPs, and CD38. These two roles underpin the later literature connecting NAD+ with aging.

2. The connection with aging

In 2000, Imai and colleagues reported that Sir2 is an NAD+-dependent deacetylase, connecting NAD+ to lifespan regulation. Over the next two decades, animal studies repeatedly showed declines in tissue NAD+ with age and improvements in mitochondrial and stem-cell function after precursor supplementation. Human evidence is much less consistent; Section III examines it separately.

3. Precursors and supplementation

NAD+ itself does not readily enter cells, so supplementation research focuses on its precursors: nicotinic acid, or niacin (NA); nicotinamide (NAM); nicotinamide riboside (NR); nicotinamide mononucleotide (NMN); and the reduced forms NRH and NMNH. In 2016, Trammell and colleagues showed that oral NR could raise human blood NAD+ to approximately 2.7 times baseline ¹. From 2018 onward, randomized trials in healthy participants and patients confirmed that NR and NMN raise blood NAD+ ^2,3,4. The first human head-to-head trial of three precursors, published in 2026, involved 65 participants over 14 days: NMN and NR increased whole-blood NAD+ to a similar extent, while nicotinamide produced only a transient increase ⁵.

4. Recent developments, 2024–2026

• The phase III NOPARK trial of NR in early Parkinson's disease missed its primary endpoint.

  Among 410 participants receiving NR 500 mg twice daily for 52 weeks, motor scores were no better than with placebo. The adjusted difference actually favored placebo by 2.72 points, below the threshold for clinical significance. Adverse events were comparable ⁶. This is the largest and longest randomized trial in the NR/NMN field to date.

• Meta-analyses of muscle function in older adults were uniformly null.

  Pooling 10 randomized controlled trials (RCTs) found no significant improvement in grip strength, walking speed, or five-times sit-to-stand performance ⁷. An NMN-specific meta-analysis reached the same conclusion ⁸, as did a review of physical performance ⁹.

• Meta-analyses of metabolic markers were null.

  Across eight NMN trials with 342 participants, fasting glucose, insulin, HbA1c, HOMA-IR, and blood lipids did not change significantly ¹⁰. An updated 2025 analysis reached the same conclusion ¹¹.

• The NICE trial in peripheral artery disease showed a signal.

  In 90 patients treated for six months, the between-group difference in six-minute walking distance was 17.6 meters. The trial prespecified a one-sided α of 0.10, making this an exploratory finding that needs confirmation ¹².

• The long COVID trial was negative.

  NR at 2,000 mg/day for 24 weeks raised NAD+ to 2.6–3.1 times baseline, but cognition, fatigue, sleep, and mood did not differ between groups ¹³.

• Whole-blood NAD+ did not vary with age.

  Across seven independent cohorts using rigorous mass-spectrometry methods, whole-blood NAD+ remained stable across ages and did not change with lifestyle interventions, apart from NR supplementation ¹⁴.

• Isotope tracing clarified what happens to oral precursors.

  Most NMN/NR is deamidated to nicotinic acid by gut microbes or broken down to nicotinamide during hepatic first-pass metabolism, then used to synthesize NAD+ through established pathways ^15,16.

• Regulatory decisions shifted.

  In 2025, the FDA withdrew its drug-exclusion determination for NMN and restored its new dietary ingredient status ¹⁷. EFSA issued a safety opinion on one β-NMN product ¹⁸.

5. What comes next

Several ongoing confirmatory trials could meaningfully answer whether NAD+ precursors benefit people: a phase III trial of NR in amyotrophic lateral sclerosis (ALS), following a pilot of the combination product EH301 that randomized 32 people and had 20 completers—encouraging results from a very small sample ¹⁹; follow-up work on NICE; NR dose-finding studies; and phase II trials of Metro Biotech's crystalline NMN drug in indications including Alzheimer's disease. Another avenue targets NAD+ consumption: CD38 inhibitors and CD38 vaccines aim to reduce losses, but evidence remains limited to animals ^20,21.

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II. Metabolic Pathways

1. Three synthesis pathways

• De novo synthesis.

  NAD+ is synthesized from tryptophan through the kynurenine pathway, primarily in the liver.

• The salvage pathway.

  NAMPT converts nicotinamide to NMN, and NMNAT then converts NMN to NAD+. NR enters the same pathway after phosphorylation to NMN by NRK1/2 ²². This is the principal route for maintaining NAD+ in mammalian tissues.

• The Preiss–Handler pathway.

  Nicotinic acid is converted to NAD+ through NAMN and NAAD.

2. How does oral NR/NMN actually work?

One common claim is that “the Slc12a8 transporter carries NMN directly into cells.” Grozio and colleagues reported this transporter in 2019 ²³. A commentary in the same journal questioned whether the evidence was sufficient ²⁴, and the original authors replied ²⁵. Imai's 2025 review cited subsequent evidence supporting Slc12a8-dependent uptake, but the transporter is expressed primarily in the small intestine and hypothalamus, and its contribution to whole-body NAD+ remains uncertain ²⁶. The dispute is unresolved.

Isotope-tracing findings are more consequential. In 2018, Liu and colleagues administered dual-labeled NR/NMN orally and found that only a small fraction of tissue NAD+ retained the intact label. Most precursor was broken down to nicotinamide during hepatic first-pass metabolism, while tissues outside the liver relied primarily on circulating nicotinamide to synthesize NAD+. Intravenous administration was required to deliver intact molecules to multiple tissues ¹⁵. In 2025, Yaku and colleagues further showed that most oral NMN/NR was deamidated to nicotinic acid by gut microbes, then synthesized into NAD+ in the liver through the Preiss–Handler pathway after enterohepatic circulation. Germ-free mice showed a markedly smaller increase in liver NAD+ after oral precursors ¹⁶. At the cellular level, NMN must first be dephosphorylated outside the cell to NR before uptake; the two then follow the same intracellular pathway ²². Independent work has also reported microbial deamidation of NMN ²⁷.

The practical implication is that the rise in blood NAD+ is real, but it reflects faster hepatic synthesis after an increased supply of nicotinamide/nicotinic acid. It does not demonstrate that intact NMN molecules entered your muscle cells. This also explains why NMN and NR have comparable effects in the head-to-head trial ⁵.

3. Reduced precursors

NRH produces NAD+ through an NRK1-independent pathway and is faster and more potent than NR in animals ²⁸; NMNH behaves similarly ²⁹. A 2026 study of chronic NRH administration in high-fat-fed mice found improved glucose tolerance, but higher doses produced toxicity signals ³⁰. Neither precursor has human data.

4. NAD+ consumption

Consumption is the other side of NAD+ decline. The strongest animal evidence concerns the age-related increase in CD38: CD38-knockout mice do not show the usual age-related fall in NAD+ ³¹. Inflammatory factors secreted by senescent cells induce high CD38 expression in macrophages, an upstream driver of tissue NAD+ decline ³². DNA damage also activates NAD+-consuming PARPs. In human skin, PARP activity rises with age and is inversely associated with NAD+ ³³. CD38 also degrades exogenous NMN, suggesting that precursor supplementation may become less efficient when CD38 is high ³¹. In 2016, Schultz and Sinclair summarized this framework as NAD+ declining because it is being destroyed ³⁴, although the framework rests primarily on animal evidence.

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III. Does NAD+ Decline with Age in Humans?

This is a central premise of the field and deserves a separate examination.

Tissues with direct measurement evidence: In skin, NAD+ was strongly inversely associated with age in 49 human samples spanning ages 0–77: r = −0.71 in males and r = −0.54 in females ³³. In the brain, 7T magnetic resonance spectroscopy in healthy volunteers found that NAD+ declined and NADH increased with age ³⁵. A 50-person cohort confirmed a positive association between brain NAD levels and ATP production rate ³⁶, and an independent methodological study found a similar direction of change ³⁷. A review estimated declines of approximately 10%–25% in brain and cerebrospinal-fluid NAD+ ³⁸.

Where evidence does not support a decline: Whole blood. A 2021 systematic review already described evidence for age-related changes in human NAD+ as “very limited” ³⁹. In 2026, the same research group measured whole-blood NAD+ across seven independent cohorts using validated mass spectrometry and found no change with age or lifestyle interventions ¹⁴.

Where evidence is insufficient: Skeletal muscle, liver, kidney, and heart. Skeletal-muscle evidence is indirect, coming from supplementation studies. After older men took NR for 21 days, muscle NAD+-related metabolites changed, but muscle NAD+ itself did not increase significantly and mitochondrial function did not improve ⁴. This was neither a direct comparison of younger and older people nor proof of deficiency.

Three methodological cautions: NAD+ can degrade substantially within minutes of sampling, and results can differ severalfold across platforms ³⁹. Changes from infancy to adulthood in the skin data reflect development, not necessarily continuing depletion in adulthood. Steady-state concentration is not the same as the flux of synthesis and degradation ¹⁵.

How to describe the evidence: There is direct evidence of age-related NAD+ decline in specific tissues, while whole-blood NAD+ does not decline. The evidence does not support a universal claim that “human NAD+ falls by a certain amount each decade,” or the use of blood NAD+ to assess the speed of aging. Evidence of NAD+ depletion in disease states, such as neurodegenerative disease and some tumors, is more consistent than in healthy aging. This suggests that depletion may be more a marker of pathology than a universal feature of normal aging.

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IV. Anti-Aging Mechanisms: What Holds Up?

“Activating sirtuin enzymes” has long been presented as the leading mechanism for NAD+'s proposed anti-aging effects. Three distinct questions need to be separated.

First: Are assays of sirtuin activators reliable? In 2010, an Amgen team showed that the apparent “activation” of SIRT1 by resveratrol, SRT1720, and related compounds depended entirely on a fluorescent group attached to the substrate; activation disappeared with native substrates ⁴⁰. In 2013, Sinclair's team proposed substrate-sequence-dependent allosteric activation as a partial reconciliation ⁴¹. The early evidence for lifespan extension through small-molecule sirtuin activation therefore had methodological weaknesses.

Second: Are sirtuins conserved longevity genes? In 2011, Burnett and colleagues found that Sir2 overexpression did not extend lifespan in worms or flies after genetic backgrounds were standardized. Earlier effects arose from a cosegregating second locus ⁴². In 2022, Brenner systematically argued that “sirtuins are not conserved longevity genes” ⁴³. This does not negate reports linking individual mammalian sirtuins, such as SIRT6, to lifespan, but it undermines the claim of a single conserved longevity pathway.

Third: Does NAD+ supplementation work through sirtuins? NAD+ is a substrate for sirtuins, PARPs, and CD38, so raising it can affect several pathways simultaneously. Changes observed after CD38 inhibitors restore NAD+ involve sirtuins, AMPK, PARP, and mTOR ²⁰. There is currently no evidence establishing sirtuins as a necessary mediator of NAD+ supplementation's effects.

What remains well grounded: The NAD+/NADH ratio directly influences mitochondrial electron-transport efficiency, and human brain NAD+ is positively associated with ATP production rate ³⁶. PARP-dependent DNA repair requires NAD+ ³³. The CD38–NAD+ axis regulates macrophage polarization and inflammation ^32,44. A 2018 review systematically covers the in-vivo animal evidence ⁴⁵.

How to describe the evidence: NAD+ biology should not be reduced to “activating sirtuins.” Effects are more likely to involve mitochondrial energy metabolism, DNA repair, and immune-inflammatory pathways. Which pathway dominates during human supplementation remains unresolved.

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V. The Human Evidence

1. NR

Table 1. Human trials of NR

NR safety studies found good tolerability at up to 1,000 mg/day over eight weeks, with increased NAD+ and methylated nicotinamide excretion ⁴⁸.

2. NMN

Table 2. Human trials of NMN

Yoshino 2021 is one of the few positive NMN studies published in a high-impact journal, but it involved only 25 participants and the debate over baseline imbalance remains unresolved. Subsequent meta-analyses evaluated conventional metabolic markers, which are different endpoints from clamp-measured muscle insulin sensitivity. The precise conclusion is that this tissue-specific signal still lacks independent confirmation and has not translated into improvements in routine glycemic measures.

3. Niacin and nicotinamide

• Niacin and cardiovascular outcomes.

  Two large RCTs in the statin era—AIM-HIGH, with 3,414 participants ⁵⁵, and HPS2-THRIVE, with 25,673 ⁵⁶—found no reduction in cardiovascular events from adding niacin. The latter found more serious adverse events. Niacin should not be used as a cardiovascular-protection strategy.

• The niacin metabolite 4PY.

  A three-cohort study published in 2024 associated the terminal niacin metabolite 4PY with major cardiovascular events over three years, with a hazard ratio of approximately 1.9 for the highest versus lowest quartile. Genetic analyses and mouse vascular-inflammation experiments supported a mechanism ⁵⁷. An accompanying commentary noted that exposure could include food fortification and that intervention trials were needed to establish causality ⁵⁸. NR and NMN also pass through nicotinamide metabolism to methylated nicotinamide and downstream products ¹, so this concern cannot be dismissed simply because the precursor has a different name.

• Nicotinamide and skin cancer.

  In ONTRAC, one year of oral nicotinamide reduced nonmelanoma skin cancers by 23% in immunocompetent people at high risk; protection disappeared after treatment stopped ⁵⁹. ONTRANS found no benefit in solid-organ transplant recipients, although underrecruitment limited its power ⁶⁰. A review of high-dose nicotinamide safety is available in ⁶¹.

• How efficiently does nicotinamide raise NAD+?

  In the head-to-head trial, 14 days of nicotinamide did not sustain an increase in whole-blood NAD+ ⁵, possibly because NNMT rapidly methylates and clears it.

• Specific deficiency states.

  A study of niacin in adults with mitochondrial myopathy, from the Ristow laboratory, exemplifies supplementation helping when NAD+ is deficient. However, it was a small, unblinded study without a placebo control, and its conclusions are limited to people with a documented deficiency.

4. A caution about a large meta-analysis

A 2022 meta-analysis of 40 articles reported that “NAD+ precursors” improved blood lipids but raised glucose ⁶². Most included trials, however, studied niacin. Niacin's lipid-lowering pharmacology differs from NR/NMN, so the compounds should not be treated as interchangeable.

5. Subjective energy, sleep, exercise, and cognition

“I have more energy since taking it” is among the most common reports from NR/NMN users. It deserves a separate look at controlled evidence.

• Fatigue and sleep.

  Three small Japanese or manufacturer-funded NMN trials reported signals. Among 108 older adults taking NMN 250 mg/day for 12 weeks, the afternoon-dosing group had better sleepiness and fatigue scores than placebo, but total sleep-quality scores did not differ between groups ⁵³. In 60 older adults treated for 12 weeks, the daytime-function component of a sleep questionnaire improved versus placebo, while the primary endpoint, a stepping test, was negative ⁶³. Among 66 middle-aged participants taking 300 mg/day for 60 days, quality-of-life scores improved by 6.5% with NMN and 3.4% with placebo, a nonsignificant difference ⁶⁴. For NR, the long COVID trial used 2,000 mg/day for 24 weeks and found no differences from placebo in fatigue, sleep, anxiety, or depression ¹³. No positive NR trial in healthy people with energy or vitality as its primary endpoint was identified.

• Exercise performance.

  In 48 amateur runners taking NMN for six weeks, power at the first and second ventilatory thresholds improved in a dose-dependent manner in the medium- and high-dose groups, but maximal oxygen uptake and peak power did not change ⁶⁵. A systematic review of 10 trials found no statistically significant improvement in physical-performance measures ⁹. Meta-analysis of grip strength, walking speed, and sit-to-stand performance was null ⁷.

• Cognition.

  In 52 older adults with mild cognitive impairment, NR 500 mg twice daily for 12 weeks doubled blood NAD+ and increased hippocampal perfusion, but memory and executive function did not differ between groups. This was a 2025 conference presentation and had not yet been formally published. Cognitive outcomes in the long COVID trial were also negative ¹³.

• Placebo effects.

  Placebo groups in these studies also improved in fatigue, sleep, and quality of life. In trials of subjective outcomes, placebo effects can commonly account for more than half of the improvement; the relevant evidence is the difference between groups. As of October 2026, those differences were either nonsignificant or limited to secondary or post-hoc endpoints, almost all in manufacturer-funded studies.

How to describe the evidence: The experience of “more energy” can be real, but existing trials have not demonstrated that it exceeds the placebo effect.

6. Biomarker endpoints

• Metabolism and blood pressure.

  In 30 overweight middle-aged and older adults treated for 28 days, the crystalline NMN drug MIB-626 reduced body weight by 1.9 kg, diastolic blood pressure by 7 mmHg, and LDL cholesterol by 18.7 mg/dL, each more than placebo. Muscle strength, aerobic capacity, insulin sensitivity, liver fat, and visceral fat did not change. Metro Biotech funded the study, and many authors were company employees or shareholders ⁶⁶. This is the most favorable NMN result on metabolic markers—and one particularly in need of independent replication.

• Inflammatory markers.

  Circulating inflammatory markers fell in several short NR trials ^4,47, but clinical outcomes were negative in the 52-week Parkinson's trial ⁶. Improvements in inflammatory markers did not translate into functional benefit.

• Skin and blood vessels.

  Nine people with Werner syndrome, a premature-aging disorder, took NR 1,000 mg/day for 26 weeks and showed reduced skin-ulcer area and improved arterial stiffness ⁶⁷. This rare-disease model cannot be extrapolated to normal aging. There are no large trials of skin outcomes in the general population.

• Epigenetic clocks and telomeres.

  No published human NR/NMN trial has used these as endpoints.

7. Population studies: dietary niacin alone

Several 2024 cohort analyses based on US NHANES data pointed in the same direction: people in the highest quartile of dietary niacin intake had approximately 26%–32% lower all-cause mortality and 25%–37% lower cardiovascular mortality than those in the lowest quartile. These associations appeared in the general population ⁶⁸ and in people with metabolic syndrome ⁶⁹, chronic kidney disease ⁷⁰, or cardiovascular disease ⁷¹. Three limitations prevent using them to support supplementation. Dietary niacin comes from meat, fish, and whole grains and is closely correlated with overall diet quality, so confounding by healthy dietary patterns cannot be excluded. Dietary recall introduces substantial measurement error. And dietary intake is not equivalent to high-dose supplements, much less NMN/NR. The positive association between 4PY and cardiovascular events published the same year ⁵⁷ appears contradictory, but may instead reflect a nonlinear relationship between adequate intake and excessive metabolic load.

The review identified no prospective cohorts using blood NAD+ or its metabolites to predict death or disease; no long-term follow-up of NR/NMN supplement users; and no Mendelian-randomization studies of NAD+ levels themselves.

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VI. Safety and Controversies

1. Higher blood NAD+ does not establish higher tissue NAD+, let alone benefit

This is the central gap in the field. In Yoshino 2021, NMN improved muscle insulin sensitivity without increasing muscle NAD+ ⁴⁹. In Elhassan 2019, NR changed the muscle metabolome without changing muscle NAD+ or mitochondrial function ⁴. At least five independent investigations show a gap between higher blood NAD+ and clinical outcomes ^6,3,13,46,7. Reported fold increases also depend on the sample matrix—whole blood, plasma, or peripheral-blood mononuclear cells—sampling time, and assay platform ³⁹. Cross-trial comparisons require care.

2. Cancer

Three levels of evidence need to be distinguished.

• Theoretical concerns.

  Tumor cells have a high demand for NAD+ synthesis. NAD+ metabolism also regulates the proinflammatory secretory phenotype of senescent cells, which can promote tumors.

• Animal signals.

  A 2023 study using an NR-uptake probe found high NR uptake in triple-negative breast cancer cells. An NR-enriched diet increased the incidence of brain metastases in mice from 3/12 to 9/11 ⁷². The NR dose was far above human supplement doses, and treatment began after tumor-cell injection. The finding concerns promotion of metastasis from an existing tumor, not cancer initiation. No specific human-equivalent dose multiple is given here because the exposure conversion has not been verified. Other reports describe NAD+ precursors suppressing growth in some tumor models. These findings do not cancel one another out: they involve different models and endpoints.

• Human data.

  Follow-up in most existing RCTs is no longer than 12 weeks, and none was designed for cancer-specific follow-up over multiple years. An eight-week NR safety study found no abnormalities ⁴⁸. The accurate conclusion is that evidence is insufficient to assess long-term cancer risk. It is neither “safe because no signal was seen” nor “carcinogenic in humans because an animal signal exists.”

Prime Lab advises people with a current cancer diagnosis or a history of cancer not to take NR/NMN.

3. Long-term safety data

Most safety data come from trials lasting 6–12 weeks with tens to hundreds of participants, alongside a small number lasting four to six months or 52 weeks ^6,12,13. Evidence is insufficient for years of use or rare serious events. Reported trials found no abnormalities in liver enzymes, uric acid, or platelets ^3,48.

4. Methyl-donor consumption

Nicotinamide generated from NR/NMN is methylated by NNMT for clearance, consuming one molecule of S-adenosylmethionine each time. Urinary methylated nicotinamide excretion increased 2.6-fold after NR in humans ¹. This is a mechanistically plausible theoretical concern, but human trials have not found increased homocysteine or disrupted one-carbon metabolism ². Routine extra methyl-donor supplementation solely because someone takes NR/NMN is not recommended; evidence does not support it.

5. Dose

Common trial doses are NR 300–1,000 mg/day, occasionally 2,000 mg, and NMN 250–900 mg/day, occasionally up to 1,200 mg. NMN dose-finding work found similar effects at 600 and 900 mg ⁵⁴, but similar results at two doses do not establish a plateau. No dose has been shown to improve health outcomes, so there is currently no answer to the question of an “optimal dose.”

6. Methodology and financial relationships

Small samples, short durations, surrogate endpoints, and company-supplied products or funding are common in this field. The tables list funding and author relationships for individual trials. The principle is to assess risk of bias first, then interpret financial relationships. Publicly funded NICE showed a positive signal, while some company-funded trials were negative; the funder alone does not establish whether a finding is true or false. Readers should nevertheless know that NR's discoverer has long advised and held shares in an NR company, that leading NMN advocates cofounded an NMN drug company, and that the two companies took opposing positions in the FDA's NMN regulatory dispute.

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VII. Regulation and the Market

1. United States

NR: its new dietary ingredient notification received no objection in 2015, followed by a GRAS “no questions” letter in 2016, allowing food uses at up to 300 mg per serving. NMN: in November 2022, the FDA excluded NMN from the definition of a dietary supplement under the drug-exclusion provision, following Metro Biotech's investigational new drug application. In September 2025, the FDA withdrew that determination, recognizing that NMN had been marketed as a supplement before authorization of the drug investigation. Its new dietary ingredient status was restored in December 2025 ¹⁷. Being outside the drug exclusion and regaining new dietary ingredient status are regulatory classification decisions, not endorsements of efficacy.

2. European Union

NR: EFSA concluded in 2019 that up to 300 mg/day was safe, and the European Commission authorized it as a novel food in 2020 ⁷³. NMN: EFSA has issued a safety opinion on one β-NMN product ¹⁸, with final market authorization awaiting a European Commission decision. A safety opinion is not market authorization, and market authorization is not an endorsement of efficacy.

3. China

NMN has not been approved as a medicine, health food, food additive, or new food ingredient; it was approved only as a new cosmetic ingredient in 2022. The National Health Commission rejected a new food-additive application in 2023, and NMN appeared again on the application-acceptance list in 2025. Cross-border e-commerce channels have tightened since 2024, but general trade, cross-border retail, personal mail, domestic production, and promotional compliance are governed by different rules. This memo therefore does not make a legal claim of a blanket ban. Prime Lab's position is not to recommend purchasing unapproved NMN products.

4. Japan

NMN has been on the list of non-drug ingredients since 2020 and can be used in food. The first NMN Food with Function Claims notification was completed in 2024. This is a company notification system, not government confirmation of efficacy.

5. The market

Estimates of the global NMN market vary widely by definition—roughly US$200–400 million in 2024. Growth is driven primarily by demand for anti-aging products rather than clinical evidence. Approximate consumer costs are US$40–55 per month for NR, US$55–80 for NMN, and several hundred to more than a thousand dollars per intravenous NAD+ infusion. Supplier market-share rankings are not included because no auditable source was available.

6. What clearance means: safety and classification, not efficacy

Readers often ask why regulators allow supplements to be sold if positive evidence is lacking. The answer is that clearance for supplements and food ingredients addresses safety and legal classification, not efficacy.

• United States.

  Under the 1994 Dietary Supplement Health and Education Act, supplements do not need to demonstrate efficacy before marketing. A new ingredient requires evidence supporting a reasonable expectation of safety ⁷⁴. NMN's exclusion in 2022 was triggered by the drug-exclusion provision: once an ingredient is authorized for investigation as a new drug, it cannot be marketed as a supplement unless it was already marketed as a supplement or food beforehand ^75,76. Metro Biotech's investigational new drug application for NMN triggered that provision. The FDA withdrew the determination in September 2025 because industry supplied evidence that NMN had been sold as a supplement before the drug application, meeting the exception ⁷⁷. New dietary ingredient status was restored in December ¹⁷. This was a dispute over legal classification; the FDA documents did not establish efficacy. NR's new dietary ingredient notification and GRAS determination likewise rested on safety data ⁴⁸, not efficacy.

• European Union.

  Novel-food assessment addresses safety alone. EFSA's NR opinion concluded that up to 300 mg/day was safe for adults ⁷⁸, and the European Commission authorized it on that basis ⁷³. The NMN opinion similarly addresses a safe dose ⁷⁹. EFSA's public documentation explicitly states that “the efficacy of the novel food is not assessed” ⁸⁰. Health claims follow an entirely separate authorization process.

• Japan.

  Foods with Function Claims use a notification system. Companies submit their own substantiation for functional claims; the Consumer Affairs Agency publishes notifications without reviewing safety and efficacy ⁸¹.

• China.

  New food-ingredient review evaluates safety, not efficacy ⁸². Health-food registration does assess efficacy, but NMN has not received such approval.

Table 3. Regulatory frameworks by jurisdiction

How to describe the evidence: Claims such as “FDA approved” or “EFSA certified effective” misrepresent these frameworks. Clearance means only that there is no reason to consider the ingredient unsafe at the proposed dose.

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VIII. Research Groups and Industry Relationships

Table 4. Research groups and the industry landscape

How to describe the evidence: Nearly all major academic voices in the field have industry relationships. Those relationships should be disclosed when citing their conclusions.

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IX. Key Points by Compound

NR: nicotinamide riboside

• Trial doses are 300–1,000 mg/day; safety data over eight weeks are reassuring ⁴⁸.
• Reliably raises blood NAD+. Clinical outcomes: negative in Parkinson's disease ⁶, no improvement in functional cardiac endpoints in heart failure ⁴⁶, negative metabolic results in men with obesity ³, and negative in long COVID ¹³. Peripheral artery disease has an exploratory signal ¹².
• Animal lifespan: no extension in the multicenter ITP trial ⁸³.
• A permitted food ingredient in the United States and European Union ⁷³.

NMN: nicotinamide mononucleotide

• Trial doses are 250–900 mg/day; short-term safety is reassuring.
• Raises blood NAD+ similarly to NR ⁵. One small trial found improved muscle insulin sensitivity ⁴⁹, while meta-analyses of metabolic markers ¹⁰ and muscle function ^7,8 were negative.
• Animal lifespan: 12 months of treatment improved metabolic and physical-performance measures, but lifespan was not an endpoint ⁸⁴. Lifespan was extended in a progeroid mouse model ⁸⁵. For normal mice, lifespan-extension evidence is limited to a preprint.
• Supplement status was restored in the United States in 2025 ¹⁷; it remains unapproved in China.

Niacin

• An effective NAD+ precursor, but doses above recommended levels can cause flushing and hepatotoxicity. Cardiovascular-outcome trials were negative and found increased adverse events ^55,56. Its metabolite 4PY is associated with cardiovascular events ⁵⁷. Not recommended for anti-aging.

Nicotinamide

• Inexpensive, but it did not sustain an increase in whole-blood NAD+ over 14 days ⁵. Its clinical value is in skin-cancer prevention for immunocompetent people at high risk ⁵⁹, rather than anti-aging.

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X. Conclusions and Prime Lab's Assessment

What the literature shows. NR and NMN reliably and reproducibly raise blood NAD+. There is evidence for age-related decline in specific tissues, but not in whole blood. Oral precursors act primarily through established nicotinamide and nicotinic-acid pathways, rather than by entering cells intact. The foundations of the sirtuin narrative have been challenged. Human randomized trials are negative for Parkinson's disease, muscle function, metabolic markers, and long COVID. Peripheral artery disease has a signal awaiting confirmation, while specific deficiency states, such as mitochondrial myopathy, have small positive studies. For animal lifespan, NR results are negative and NMN evidence is limited to a preprint. Short-term safety is reasonably reassuring; long-term evidence is missing. Cancer and 4PY-related findings warrant attention.

Our interpretation—explicitly an inference. If NAD+ precursors ultimately establish a useful role in humans, three settings seem most plausible: documented NAD+ deficiency, such as mitochondrial disease or specific metabolic defects; particular diseases involving inflammation or peripheral vascular dysfunction; and tissues with high demands for NAD+-dependent DNA repair, with skin-cancer prevention already providing an example. For “whole-body anti-aging in healthy people,” even a workable trial endpoint has yet to be established.

Our recommendation. Healthy adults do not need NR or NMN for “anti-aging.” For those who nevertheless choose to take them, trial doses appear safe in the short term, but measurable health benefits should not be expected, and a blood NAD+ test should not be used as proof that they “work.” Feelings of greater energy need to be considered alongside placebo effects. People with a history of cancer should not take them, and those at cardiovascular risk should not treat niacin as a wellness supplement. The confirmatory trials reporting over 2026–2028 are worth watching, rather than the next small positive study.

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