NAD+: mechanism of action

Nicotinamide adenine dinucleotide (NAD+) is a dinucleotide coenzyme built from an adenine nucleotide linked to a nicotinamide nucleotide, and it is the parent compound of a family of precursors that includes nicotinamide riboside (NR), nicotinamide mononucleotide (NMN), and nicotinamide. In the research literature it is also written as NAD, and its oxidised and reduced forms are distinguished as NAD+ and NADH. The evidence block supplied for this page does not give a sequence, formula or molecular weight for NAD+, so none is stated here. The work described below centres on NAD+ as a redox coenzyme and as a substrate for NAD+-consuming enzyme families, principally the sirtuins and the poly(ADP-ribose) polymerases, with precursor compounds used to raise or maintain NAD+ availability in the models studied.

NAD+ sits at the intersection of two roles: it carries electrons in oxidation-reduction reactions, and it is consumed as a substrate by enzymes that transfer ADP-ribose or remove acetyl groups from proteins. Because those enzymes use NAD+ itself rather than merely being influenced by it, the size of the available NAD+ pool is treated in the literature as a variable that can be manipulated experimentally. The trials and studies below test that idea in different populations, using different precursors and different routes of administration.

Research Studies

NAD+ and whole-blood NAD+ change in healthy adults

A clinical trial has been designed to assess the absorption, safety and efficacy of an oral NAD+ supplement in healthy adults [1]. The primary question is the change in NAD+ levels in whole blood from baseline to day 56, comparing the NAD+ supplement with placebo. Participants complete questionnaires, provide blood samples, consume either the supplement or placebo for 55 days, and undergo evaluation of endothelial function [1]. This is a registered trial protocol; the evidence block does not report results, so no effect size or direction of change is stated here.

Nicotinamide and retinal nerve cell layer thickness in primary open-angle glaucoma

The NADIR trial is testing whether high-dose nicotinamide, a vitamin B3 supplement, can protect retinal nerve cells in adults with primary open-angle glaucoma who are already receiving standard eye drops or laser treatment [2]. The primary question is whether adding nicotinamide to standard therapy slows the rate of thinning of the inner retinal nerve cell layer, measured by a non-invasive eye scan, compared with standard therapy alone over 12 months [2]. Participants are randomly assigned to treatment or control; the treatment group takes nicotinamide tablets by mouth starting at 1.5 grams per day [2]. The evidence block describes the design and starting dose only, and does not report outcomes.

Nicotinamide riboside and six-minute walk distance in peripheral artery disease

The NICE-PAD II trial is testing the hypothesis that, among people with peripheral artery disease aged 50 and older, participants randomised to nicotinamide riboside will show greater improvement or less decline in six-minute walk distance at six-month follow-up than those randomised to placebo [3]. The study randomises 250 participants with PAD to nicotinamide riboside or placebo for six months [3]. The primary outcome is change in six-minute walk distance at six-month follow-up; secondary outcomes include the Walking Impairment Questionnaire distance score, the PROMIS Mobility score, and calf muscle perfusion measured by magnetic resonance arterial spin labelling [3]. No results are given in the evidence block.

Nicotinamide and post-COVID syndrome in patients with documented tryptophan deficiency

An observational study is examining CICR-NAM, a nicotinamide formulation developed as a food for special medicinal purposes, in patients with post-COVID syndrome [4]. The rationale given is that changes in tryptophan metabolism, energy metabolism and the gut microbiome may occur in post-COVID syndrome, and that in an earlier nutritional study patients with COVID-19 recovered physical performance more quickly when taking nicotinamide, with responders developing post-COVID syndrome less frequently [4]. The CICR-NAM tablets were developed at the University Hospital Schleswig-Holstein in Kiel to release the active substance selectively in the lower intestine and have been reported as very well tolerated in several studies [4]. Patients with post-COVID syndrome and documented tryptophan deficiency may take the formulation as part of the study [4]. This is an observational design, not a randomised comparison, and the evidence block does not report outcomes.

MIB-626 (β-nicotinamide mononucleotide) in adults with Down syndrome

A trial is determining the safety and tolerability of increasing doses of MIB-626, a microcrystalline form of β-nicotinamide mononucleotide (NMN), given daily for 28 consecutive days to adults with Down syndrome [6]. The study also explores pharmacokinetics, described as how the drug moves through the body over time, and pharmacodynamics, described as how the drug affects the body in different ways [6]. Participants are monitored for adverse events, with laboratory tests of blood counts, chemistries and coagulation profile, and electrocardiogram [6]. The trial will enrol 24 adults with Down syndrome [6]. The evidence block reports the design and population only.

Topical nicotinamide riboside and signs of facial skin ageing

A trial is evaluating topical niacinamide riboside, also known as nicotinamide riboside, for signs of facial skin ageing [7]. The background given is that nicotinamide riboside is an endogenous compound and a precursor to NAD+, and that research published by Maussudi et al. in 2012 reported that skin NAD+ levels were negatively correlated with age in both males and females, and that aged skin was also correlated with an increase in DNA damage [7]. On that basis it has been proposed that supporting skin NAD+ with precursors such as nicotinamide riboside may be a strategy against DNA damage associated with undesirable signs of skin ageing, supporting skin cell resilience [7]. The evidence block states that use of nicotinamide riboside as a dietary supplement has produced effective, efficient and reproducible results, but the sentence is truncated and does not specify the outcome measured, so no specific skin endpoint is reported here.

Nicotinamide riboside and brain blood vessel health, memory and physical function in Parkinson's disease

A clinical trial is testing whether nicotinamide riboside, a form of vitamin B3 also known as NR, can improve blood vessel health in the brain, memory and physical function in eligible participants [8]. The main questions are whether NR can improve non-invasive measures of blood vessel health in the brain, and whether it can improve memory testing results and physical function [8]. Participants receiving NR are compared with participants receiving placebo to see whether NR has beneficial effects [8]. The evidence block notes that NR is considered investigational for this study because it is not yet established for this specific use [8]. No results are reported.

Comparison of the models and populations studied

The table below sets out the populations, compounds and primary outcomes named in the evidence block. It is a summary of study designs, not of findings.

Where the evidence is animal-only or in vitro

The evidence block supplied for this page consists of registered clinical trial records and one observational study record, all in human populations, together with one reference-only item. It does not contain animal-only or in vitro studies of NAD+ mechanism, and no such claim is made here. The reference-only item concerns Guizhi Wuling Decoction, a combined prescription of the classical formulas Wuling San and Guizhi Fuling Wan, which has been clinically applied for cardiovascular diseases and for which previous studies have reported cardioprotective and anti-fibrotic effects; that work reports a network pharmacology, molecular docking and multi-omics investigation of myocardial fibrosis and mitochondrial homeostasis [9]. It is included as supporting context for the broader study of mitochondrial homeostasis and fibrosis, and it is not a study of NAD+ or of an NAD+ precursor.

What the record does and does not establish

Across the records above, the recurring design is a randomised comparison of an NAD+ precursor against placebo, with a biomarker or functional endpoint measured at a fixed time point [1][3][6][8]. Two records use nicotinamide rather than NAD+ or nicotinamide riboside, and both are in defined clinical populations rather than healthy volunteers [2][4]. One record uses a topical route and a skin endpoint [7]. None of the records in the evidence block reports a completed result, an effect size, or a between-group difference, so no claim about efficacy in any population can be supported from this material. The mechanistic premise common to the records is that NAD+ is a coenzyme and a precursor target, and that supplying a precursor may alter the size or availability of the NAD+ pool in the tissue studied [7].

If you are reading this for personal health reasons

The materials described on this page are sold for laboratory research use only. We do not provide dosing information, medical guidance, or recommendations for personal use of any compound. Anyone considering a compound for themselves should speak to a licensed clinician.

Sources

• [1] A Clinical Trial to Assess the Absorption, Safety, and Efficacy of an Oral Nicotinamide Adenine Dinucleotide (NAD+) Supplement in Healthy Adults — https://clinicaltrials.gov/study/NCT07692633
• [2] Nicotinamide for Retinal Protection in Primary Open-Angle Glaucoma (NADIR Trial) — https://clinicaltrials.gov/study/NCT07808333
• [3] The NICE-PAD II Trial — https://clinicaltrials.gov/study/NCT07782671
• [4] Observational Study With CICR-NAM as a Food for Special Medicinal Purposes in Post-COVID Syndrome (PCS) — https://clinicaltrials.gov/study/NCT07798570
• [6] NAD Augmentation to Prevent or Reverse Alzheimer's Disease in People With Down Syndrome — https://clinicaltrials.gov/study/NCT07278492
• [7] Efficacy of Topical Niacinamide Riboside on the Signs of Facial Skin Aging — https://clinicaltrials.gov/study/NCT07774000
• [8] NAD Supplementation in Parkinson's Disease — https://clinicaltrials.gov/study/NCT07703137
• [9] Guizhi Wuling Decoction alleviates myocardial fibrosis by restoring mitochondrial homeostasis: Evidence from network pharmacology, molecular docking, and multi-omics integration. — https://pubmed.ncbi.nlm.nih.gov/42462419/