Nicotinamide riboside research: what human trials have measured

Prepared by: Research Desk. Sources are linked for verification.

Nicotinamide riboside (NR) is one of the most studied NAD+ precursors in people. Headlines usually ask whether it "works". This explainer asks a narrower and more useful question: in each human trial, what exactly was measured, in which tissue, and with what kind of study design?

That framing matters. "NAD+ went up" can describe whole blood, a subset of white blood cells, a muscle biopsy, a brain scan or spinal fluid. These are different measurements with different meanings. For the wider biochemistry of NAD+ and its precursors, start with our NAD+ guide. This page focuses on the NR trial record itself.

Why NR became a research target

Two observations drew researchers to NR.

The first is about age. A study of human tissue samples reported lower NAD+ levels in older donors, alongside markers of oxidative stress and increased activity of PARP, an enzyme family that consumes NAD+ during DNA repair [6]. This was an observational tissue study. It describes an association with age, not a cause, and it did not test any precursor.

The second is about absorption. A 2016 study in mice and humans reported that orally taken NR was bioavailable and raised the blood NAD+ metabolome. The authors described NR as "uniquely" orally bioavailable compared with other precursors they examined [1]. NR enters the NAD+ salvage pathway, where it is converted to nicotinamide mononucleotide (NMN) and then to NAD+ [7].

Together these set up the hypothesis behind most later trials. If NAD+ is lower in older tissue and NR raises NAD+ in blood, does NR also change NAD+ in the tissues that matter, and does that change anything measurable downstream?

Four questions to ask of any NR trial

Before reading individual studies, it helps to have a checklist. We apply the same four questions to each trial below.

1. Which molecule? NAD+ itself, its reduced form NADH, or related metabolites such as nicotinic acid adenine dinucleotide (NAAD) and methylated nicotinamide products. Some trials report the whole "NAD+ metabolome" rather than NAD+ alone.

2. Which sample? Whole blood, peripheral blood mononuclear cells (PBMCs, a type of white blood cell), skeletal muscle, cerebrospinal fluid, or brain tissue measured by imaging.

3. Which method? Mass spectrometry, enzymatic assays and magnetic resonance spectroscopy produce numbers that cannot be compared directly.

4. Which design? Single-arm or randomized, placebo-controlled or not, crossover or parallel, and how many participants.

The human trials, one by one

Bioavailability: mice and humans (2016)

Trammell and colleagues combined mouse experiments with small human studies [1]. Their human work tracked blood metabolites after oral NR. They reported increases across the blood NAD+ metabolome. They also identified NAAD as a particularly sensitive marker of increased NAD+ metabolism. NAAD has since appeared as a readout in several later trials.

What it measured: blood NAD+ and related metabolites. What it did not measure: any health outcome. It was a pharmacokinetic and biomarker study.

Tolerability and blood NAD+ in middle-aged and older adults (2018)

Martens and colleagues ran a randomized, placebo-controlled crossover trial in healthy middle-aged and older adults [2]. In a crossover design every participant receives both NR and placebo in separate periods, which reduces the number of people needed.

The headline findings, as the title states, were that chronic NR was well tolerated and that it elevated NAD+. The NAD+ increase was measured in PBMCs. The trial also collected exploratory cardiovascular measures, including blood pressure and arterial stiffness. The authors framed these as preliminary signals that would need larger trials, not as established findings [2].

Sample: PBMCs. Design: small randomized crossover. Key caution: PBMC NAD+ is not the same measurement as whole-blood NAD+ or tissue NAD+.

Skeletal muscle in older men (2019)

Elhassan and colleagues took muscle biopsies from a small group of older men before and after a period of NR intake [3]. They reported that NR "augments" the aged muscle NAD+ metabolome. The clearest changes were in downstream metabolites such as NAAD and methylated nicotinamide products, rather than a large shift in muscle NAD+ itself. The authors also described transcriptomic changes and lower levels of some circulating inflammatory cytokines. They reported no measurable change in muscle mitochondrial bioenergetics over the study period.

Sample: muscle tissue plus blood. Design: small, short-duration human study. Key caution: "signatures" in gene expression and cytokines are molecular readouts, not functional outcomes.

Brain and spinal fluid in Parkinson's disease: NADPARK (2022)

The NADPARK study was a randomized phase I trial in people with newly diagnosed Parkinson's disease [4]. Phase I trials focus mainly on tolerability and on whether a compound reaches its intended target.

NADPARK used phosphorus magnetic resonance spectroscopy (31P-MRS) to estimate NAD levels in the brain. It also measured the NAD metabolome in cerebrospinal fluid. The authors reported increased brain NAD levels in a subset of participants who received NR, along with changes in cerebrospinal fluid NAD metabolites, and reported that NR was well tolerated [4]. Movement-related scores were secondary, exploratory measures. A phase I trial of this size is not designed to establish effects on disease course.

Samples: brain (imaging) and cerebrospinal fluid. Design: small randomized phase I. Key caution: NADPARK is one of the few NR studies to measure central nervous system tissue directly.

Older adults with mild cognitive impairment (2024)

Orr and colleagues ran a randomized, placebo-controlled trial of NR in older adults with mild cognitive impairment [5]. Blood NAD+ rose in the NR group. Cognitive measures did not differ meaningfully from placebo in this small trial. The study shows a recurring pattern in NR research: a clear biomarker change in blood alongside little or no change in the functional outcome measured.

Sample: blood, with cognitive testing. Design: small randomized placebo-controlled trial.

Trials at a glance

What the reviews add

Reviews put these single trials in context. A 2021 review asked, in its title, whether NAD+-increasing strategies could change cardiometabolic health [7]. The authors noted that human trials were mostly small and short. They found that reliable rises in NAD+ markers had not translated into consistent changes in cardiometabolic outcomes.

A 2026 PRISMA-guided systematic review gathered preclinical and clinical studies of NAD+ supplementation in an anti-aging and wellness context [8]. When reading a review like this, keep the animal and cell evidence separate from the human evidence. They are very different in how far they apply to people.

Where NR sits on the regulatory map

In the U.S., NR is sold as a dietary supplement ingredient. Dietary supplements do not go through FDA approval before they are marketed. Manufacturers are responsible for safety and for truthful labelling [9]. Supplement status says nothing about whether any trial outcome has been established. Our U.S. legal status explainer covers NR, NMN and IV NAD+ in detail.

Tools for comparing NAD+ blood tests

The trials above show that NAD+ numbers depend heavily on sample type and method. That makes the choice of an at-home NAD+ blood test a technical decision, not a branding one. The criteria below separate a credible test from a vague one.

• What is measured. Does the report give NAD+ alone, or NAD+ together with related metabolites? Is the result for whole blood or for a specific cell fraction? A test that names its analyte and sample matrix precisely is more useful than one that reports an "NAD score".

• Assay method and validation. Look for a named method, such as an enzymatic cycling assay or mass spectrometry, and for published validation data covering precision and stability of the dried or shipped sample.

• Reference range. Check how the range was built: how many people, what ages, and which sample type. A range from a different matrix cannot be applied to the result.

• Comparability. No consumer result can be lined up against trial figures from PBMCs, muscle or brain imaging. A good provider says so plainly.

• Price transparency. Is the price per kit stated clearly, including any repeat-test pricing? Are there hidden lab or shipping fees?

• Data privacy. Look for a clear policy on who stores the results, for how long, and whether data are shared or sold.

Providers that publish their method, validation and reference-range data are worth choosing over cheaper kits that do not.

Frequently asked questions

Is nicotinamide riboside the same as niacin?

No. NR is one of several forms of vitamin B3, alongside nicotinamide and nicotinic acid. All of them feed into NAD+ synthesis, but through different enzymatic routes. Trammell and colleagues reported that NR behaved differently from other forms in their oral bioavailability work [1].

Does a rise in blood NAD+ mean tissue NAD+ rises too?

Not necessarily. The muscle study reported changes mainly in downstream metabolites rather than a large shift in muscle NAD+ [3]. NADPARK reported brain NAD changes in only a subset of participants [4]. Blood findings and tissue findings need to be read separately.

Have NR trials shown changes in health outcomes?

The randomized human trials consistently report changes in NAD+-related biomarkers and report that NR was well tolerated. Functional outcomes, such as cognition in the mild cognitive impairment trial, have generally not differed from placebo in these small studies [5]. Reviews call for larger and longer trials [7]. More on how this site evaluates evidence is on our About page.

Last updated: 19 October 2026.

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• NAD Peptide Labs home

• Is NAD+ legal? NMN, NR and IV NAD+ under U.S. rules

• NAD+ explained: biochemistry, precursors, testing and human evidence

• NAD+ test buyer's guide: how at-home blood tests work and compare

• Reading an NAD+ test report: units, sample types and reference ranges

• NAD+ books: an evidence-graded reading list on sirtuins and aging

• NMN vs NAD+: precursor and coenzyme, explained

Not medical advice. This page reports published research and regulatory records for information only.

Research-only notice: Content on this site is provided for research and educational purposes only and is not intended for human use. It is not medical advice.

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