Nicotinamide Riboside: A Literature Course

This course organises the published literature on nicotinamide riboside (NR) into six modules. It describes what researchers studied, what they measured and what they reported, and it ends each module with the limits of that evidence. This page is for educational purposes only and is not medical advice; consult a licensed physician before making any health decision. Nothing here is a protocol, a recommendation or a statement about what any individual should do.

Module 1: What Nicotinamide Riboside Is and How It Has Been Studied

Nicotinamide riboside is a pyridine nucleoside — nicotinamide joined to a ribose sugar — and is classified in the literature as a vitamin B3 form and a precursor to nicotinamide adenine dinucleotide (NAD+). It is a small molecule, not a peptide; it appears on this site because the NAD+ literature is frequently discussed alongside peptide research. A 2023 review of NAD+ precursors described nicotinamide mononucleotide (NMN) and NR as compounds present in small amounts in foods such as milk, and examined their potential dietary contribution to NAD+ status (PMID 37273100).

Forms used in studies

• Nicotinamide riboside chloride — the crystalline salt used in most published human and rodent work; one mouse study of ischaemic injury used nicotinamide riboside chloride and reported reduced hippocampal damage and preserved cognitive function (PMID 35585298).
• Reduced nicotinamide riboside (NRH) — a dihydro form; researchers reported that a reduced form of NR protected the cochlea against aminoglycoside-induced ototoxicity through SIRT1 activation in a preclinical model (PMID 35658237).

Study types in the record

The evidence base includes cultured-cell work, such as alcohol-stimulated macrophages in which NR was reported to attenuate inflammation and oxidative stress (PMID 33846538); rodent disease models including glucocorticoid-induced glaucoma (PMID 38949632); first-in-human bioavailability work (PMID 27721479); and randomised clinical trials in obesity (PMID 32320006), Parkinson's disease (PMID 35235774) and peripheral artery disease (PMID 38871717).

Limits of the evidence in Module 1

Definitions and chemistry are settled, but the study set is heterogeneous: different NR forms, different species and widely different endpoints. A 2023 appraisal in Science Advances examined what is really known about NR supplementation in humans and concluded that firm conclusions are constrained by small sample sizes and short durations (PMID 37478182).

Module 2: Mechanism as Described in the Literature

The mechanistic account in published papers is consistent in outline. NR enters cells and is phosphorylated by nicotinamide riboside kinases to nicotinamide mononucleotide, which is then adenylylated to NAD+. NAD+ serves as a redox cofactor and as a substrate for NAD+-consuming enzymes including the sirtuins. Because of that substrate role, most mechanistic papers test whether NR raises NAD+ and whether downstream sirtuin activity changes.

Sirtuin-linked findings

In alcohol-stimulated macrophages, researchers reported that NR attenuated inflammation and oxidative stress and attributed the effect to sirtuin 1 activation (PMID 33846538). A separate group reported that a reduced form of NR protected cochlear tissue from aminoglycoside-induced damage, again via SIRT1 activation (PMID 35658237).

Mitochondrial and tissue-remodelling findings

In a model of glucocorticoid-induced glaucoma, the study reported that NR mitigated mitochondrial damage and extracellular matrix deposition (PMID 38949632). In humans, a twin study reported improvements in muscle mitochondrial biogenesis and satellite cell differentiation alongside shifts in gut microbiota after NR supplementation (PMID 36638183).

Central nervous system NAD+

The NADPARK phase I trial reported that NR supplementation raised NAD+ levels in the brain in a subset of participants with Parkinson's disease and that those with a measurable cerebral NAD+ increase showed altered cerebral metabolism (PMID 35235774).

Limits of the evidence in Module 2

Mechanistic claims rest largely on cells and rodents, where doses, exposures and tissue access differ from human supplementation. Reviewers have cautioned that a rise in a blood NAD+ marker does not establish that any particular tissue pathway was engaged, and that mechanism-to-outcome extrapolation in humans remains unproven (PMID 37478182).

Module 3: Reported Outcomes by Study

The table below lists the model, the endpoint and what the authors reported. It is a summary of published results, not a statement of expected effect.

Limits of the evidence in Module 3

Outcomes diverge by design. Biomarker endpoints such as blood NAD+ moved reliably (PMID 27721479), while clinically meaningful endpoints have been inconsistent, as in the peripheral artery disease trial where the primary analysis did not show a significant benefit (PMID 38871717). Several studies were phase I, open-label or conducted in small, specific populations, so the results do not generalise to healthy adults. A published appraisal concluded that the human literature does not yet support broad conclusions about clinical effect (PMID 37478182).

Module 4: Nicotinamide Riboside Side Effects: What Studies Report

Adverse-event reporting in the NR literature is concentrated in a small number of human trials, most lasting weeks to months.

• The first-in-human bioavailability study reported that single oral doses of 100 mg, 300 mg and 1000 mg were tolerated without serious adverse events while producing dose-dependent NAD+ metabolome increases (PMID 27721479).
• In the NADPARK phase I trial, researchers reported that NR at 1000 mg per day for 30 days was safe and well tolerated in participants with newly diagnosed Parkinson's disease (PMID 35235774).
• The six-week randomised study in healthy obese adults administered 1000 mg per day and reported metabolic and body-composition measurements rather than a signal of harm at that exposure (PMID 32320006).
• The NICE randomised clinical trial in peripheral artery disease collected safety data alongside its walking-performance endpoints over six months of supplementation (PMID 38871717).
• A critical review of human NR studies emphasised that tolerability findings come from small, short trials and that long-term safety has not been established (PMID 37478182).

Limits of the evidence in Module 4

Short trials in modest numbers of participants cannot detect uncommon events, and preclinical protection studies in cochlea, retina or brain tissue were not designed to characterise human safety (PMID 35658237, PMID 38949632). Populations such as pregnancy, childhood, advanced organ disease and active cancer are largely absent from the published trials, and reviewers have specifically flagged the absence of long-duration human safety data (PMID 37478182).

Module 5: Pharmacokinetics Where Data Exist

The pharmacokinetic literature is anchored by the 2016 Nature Communications study, which reported that NR is uniquely and orally bioavailable in mice and humans and that single oral doses of 100 mg, 300 mg and 1000 mg produced dose-dependent increases in the blood NAD+ metabolome (PMID 27721479). That work used the blood NAD+ metabolome, rather than intact NR in plasma alone, as the readout, because NR is rapidly metabolised after absorption.

Dietary exposure

A 2023 review of NAD+ precursors described NR and NMN as present in foods in small quantities and discussed how such dietary intake compares with supplemental exposure (PMID 37273100).

Tissue distribution questions

Whether oral NR raises NAD+ beyond blood has been examined directly in only a few studies; the NADPARK trial used brain imaging and reported cerebral NAD+ increases in a subset of participants receiving 1000 mg per day for 30 days (PMID 35235774), and the twin study assessed skeletal muscle outcomes after supplementation (PMID 36638183).

Limits of the evidence in Module 5

Formal multi-compartment pharmacokinetic modelling, steady-state accumulation data and comparisons across NR forms are sparse in the published record. Reviewers noted that blood NAD+ changes are the most reproducible finding and that their relationship to tissue NAD+ and to clinical endpoints has not been resolved (PMID 37478182).

Module 6: Regulatory Status, Stated Factually

Regulatory status differs from research status, and the two are often conflated.

• United States. Nicotinamide riboside chloride has been marketed as a dietary ingredient in supplements following new dietary ingredient notifications and generally recognised as safe (GRAS) notifications to the U.S. Food and Drug Administration. It is not an FDA-approved drug, and no NR product has been approved for the treatment, prevention or cure of any disease.
• Research-use-only material. NR sold by chemical suppliers for laboratory work is typically labelled research use only, which means it is not intended for human or veterinary use and is not manufactured to pharmaceutical standards.
• Compounding. Pharmacy compounding under U.S. law generally draws on FDA-approved drug substances or substances that appear on the applicable bulk drug substance lists. NR's status as a dietary ingredient rather than an approved drug substance means it is not a standard compounded pharmaceutical.
• European Union. Nicotinamide riboside chloride has been evaluated under novel food rules, with authorised conditions of use for food supplements defined by that process.
• Clinical research. Trials such as the NADPARK phase I study and the NICE randomised clinical trial were conducted under research authorisations with defined protocols and consent, not as consumer use (PMID 35235774, PMID 38871717).

This section is general regulatory information and is not legal advice; rules differ by jurisdiction and change over time.

Limits of the evidence in Module 6

Supplement availability reflects food-law categories, not a regulator's judgement that a clinical benefit was demonstrated. The published clinical record remains limited in size and duration, a point made explicitly in a review of the human data (PMID 37478182).

What the Studies Did Not Test

Across the verified literature summarised here, several questions were not addressed:

1. Long-term outcomes. No cited trial followed participants for years; the longest human exposures described here were measured in months (PMID 38871717, PMID 36638183).
2. Hard clinical endpoints. Mortality, cardiovascular events and disease incidence were not endpoints in the cited studies; endpoints were biomarkers, imaging, function tests or tissue measures (PMID 32320006, PMID 35235774).
3. Head-to-head comparisons. The cited work did not directly compare NR with NMN or other NAD+ precursors for clinical outcomes, although a review discussed both as dietary precursors (PMID 37273100).
4. Combination use. Interactions with medications, and use alongside other supplements or peptides, were not characterised in these papers.
5. Translation of preclinical protection. Cochlear, retinal, macrophage and stroke-model findings were reported in cells and animals and were not tested as human treatments in the cited record (PMID 35658237, PMID 35585298, PMID 33846538, PMID 38949632).

The overall picture from the published literature is that NR reliably raises NAD+-related blood markers and is generally described as tolerated at the doses and durations studied, while clinical endpoint results have been mixed and the evidence base remains small. A benefit reported in one small population, such as improved coordination and eye movements in ataxia telangiectasia (PMID 37899683), does not indicate what would happen in a different population.

References

• Nicotinamide riboside is uniquely and orally bioavailable in mice and humans (Nature Communications, 2016)
• Nicotinamide riboside supplementation alters body composition and skeletal muscle acetylcarnitine concentrations in healthy obese humans (The American Journal of Clinical Nutrition, 2020)
• Nicotinamide riboside, an NAD(+) precursor, attenuates inflammation and oxidative stress by activating sirtuin 1 in alcohol-stimulated macrophages (Laboratory Investigation, 2021)
• The NADPARK study: A randomized phase I trial of nicotinamide riboside supplementation in Parkinson's disease (Cell Metabolism, 2022)
• Acute Treatment with Nicotinamide Riboside Chloride Reduces Hippocampal Damage and Preserves the Cognitive Function of Mice with Ischemic Injury (Neurochemical Research, 2022)
• A reduced form of nicotinamide riboside protects the cochlea against aminoglycoside-induced ototoxicity by SIRT1 activation (Biomedicine & Pharmacotherapy, 2022)
• Nicotinamide riboside improves muscle mitochondrial biogenesis, satellite cell differentiation, and gut microbiota in a twin study (Science Advances, 2023)
• NAD+ Precursors Nicotinamide Mononucleotide (NMN) and Nicotinamide Riboside (NR): Potential Dietary Contribution to Health (Current Nutrition Reports, 2023)
• What is really known about the effects of nicotinamide riboside supplementation in humans (Science Advances, 2023)
• Long-Term Nicotinamide Riboside Use Improves Coordination and Eye Movements in Ataxia Telangiectasia (Movement Disorders, 2024)
• Nicotinamide riboside for peripheral artery disease: the NICE randomized clinical trial (Nature Communications, 2024)
• Protective Effect of Nicotinamide Riboside on Glucocorticoid-Induced Glaucoma: Mitigating Mitochondrial Damage and Extracellular Matrix Deposition (Investigative Ophthalmology & Visual Science, 2024)