Blood NAD+ can increase without an improvement in measured cognition. Three human trials of NAD+ precursors show how to separate a moved biomarker from a demonstrated anti-aging benefit.
A supplement label announces that it “boosts NAD+,” and beside it sits a quieter implication: that boosting NAD+ means slowing aging. The first is a biomarker claim that requires measurement. The second is a broader outcome claim. Three placebo-controlled trials of the NAD+ precursors nicotinamide riboside (NR) and nicotinamide mononucleotide (NMN) map the distance between them unusually well, because together they contain a clear biomarker success, a functional metabolic finding, and a trial that did not improve its primary cognitive outcome.[1][2][3]
The ladder from molecule to outcome
NAD+ (nicotinamide adenine dinucleotide) participates in cellular metabolism and serves as a co-substrate for enzymes: a molecule used in their reactions. Martens and colleagues describe its role in enzyme pathways linked to the benefits of calorie restriction as a rationale for studying NAD+ precursors in aging humans. That biological rationale motivates a trial; it does not supply the trial’s outcome.[1]
Three kinds of result get confused in anti-aging marketing. A biomarker is a measurable biological signal, such as the concentration of NAD+ in blood. A surrogate endpoint is used to stand in for a clinical outcome; treating a biomarker as a reliable substitute requires evidence linking changes in it to that outcome in the relevant context. A clinical outcome is something a person actually experiences: cognition, cardiovascular events, survival. NAD+ concentration is a biomarker. The three trials below do not validate blood NAD+ as a substitute for a longevity outcome, and none tested lifespan.[1][2][3]
Six weeks of NR in healthy middle-aged and older adults
In 2018, Martens, Seals and colleagues published a 2 × 6-week randomized, double-blind, placebo-controlled crossover trial of chronic NR supplementation in healthy middle-aged and older adults. A crossover design gives each participant both the supplement and placebo in separate periods, which lets researchers compare each person against themselves.[1]
The trial delivered a clean biomarker answer: NR was well tolerated and effectively stimulated NAD+ metabolism. It also offered what the authors themselves called initial insight into physiological function, and they wrote that future clinical trials should further assess the potential benefits of NR for reducing blood pressure and arterial stiffness in this group.[1]
The authors proposed blood pressure and arterial stiffness as questions for future trials. Preliminary physiological observations are not established cardiovascular benefits, and a six-week treatment period does not test lifespan. A careful summary is that NR stimulated NAD+ metabolism in this trial, while the authors framed the physiological observations as preliminary and proposed further trials.[1]
Ten weeks of NMN in women with prediabetes
Yoshino, Imai, Klein and colleagues took a different precursor and a more specific population. Their 2021 trial was a 10-week, randomized, placebo-controlled, double-blind study of NMN in postmenopausal women with prediabetes who were overweight or obese.[2]
This trial measured function, not just chemistry. Insulin-stimulated glucose disposal, assessed with the hyperinsulinemic-euglycemic clamp (a technique that directly quantifies how much glucose tissue clears under a controlled insulin level), increased after NMN supplementation but did not change after placebo. Skeletal muscle insulin signaling, measured as phosphorylation of the AKT and mTOR proteins, increased as well, and the researchers observed up-regulated expression of genes related to muscle remodeling.[2]
That is a real functional metabolic finding, and it should not be waved away as “just a biomarker study.” It is equally important not to stretch it. The participants were a defined group, postmenopausal women with prediabetes and excess weight, studied for ten weeks. The trial did not examine healthy aging generally, did not measure aging itself, and says nothing about lifespan. A demonstration that NMN can improve muscle insulin sensitivity in one population is evidence about that population and that endpoint.[2]
Twelve weeks of NR in mild cognitive impairment: the outcome rung
The most instructive recent result is a phase-II pilot from Martens and colleagues in older adults with amnestic mild cognitive impairment (aMCI), a form of cognitive impairment centered on memory. The rationale was direct: declining NAD+ may elevate Alzheimer's disease risk, so raising NAD+ might support cognition and cerebral blood flow.[3]
The 12-week double-blind, randomized, placebo-controlled pilot saw 42 participants complete the study, 22 on NR and 20 on placebo. Adherence was similar between groups, and blood NAD+ increased twofold in the NR group. The treatment therefore changed the intended blood measurement.[3]
The measured clinical results were different. There were no improvements in cognitive function, which was the primary outcome, and no improvements in total cerebral blood flow or blood pressure, the secondary outcomes. Exploratory analyses did reveal potential increases in regional cerebral blood flow, particularly in the hippocampus, and the authors framed that as a reason for future studies of regional effects over longer treatment durations.[3]
An exploratory finding can identify a question for a later confirmatory study. It should not be substituted for the result of the prespecified primary endpoint. The fair reading of this pilot is neither “NR fails for the brain” nor “NR helps the hippocampus.” In 42 completers over 12 weeks, NAD+ doubled, cognition did not improve, and the exploratory regional blood-flow findings provide a hypothesis for follow-up.[3]
| Evidence rung | Example from these trials | What it cannot establish |
|---|---|---|
| Biomarker | NAD+ doubled in MCI | Longevity benefit |
| Metabolic function | Insulin sensitivity rose | General aging benefit |
| Cognitive outcome | No improvement in MCI | Lasting benefit or harm |
Safety signals deserve the same precision
The MCI pilot reported no serious adverse effects, and the 2018 trial described NR as well tolerated.[1][3] That is reassuring within its boundaries: small groups, six to twelve weeks, specific preparations. It is not blanket safety for every precursor, dose, product quality level, or multi-year use; absence of reported serious harm in a pilot is a starting observation, not a long-term safety profile.
The same discipline applies to commercial materials. A chemical purity percentage on a laboratory reagent label is a chemical specification, and research-use materials should not be consumed or self-administered. This article reports no Chudik Scientific measurements of NAD+ levels and does not establish that any research material reproduces a trial's characterized preparation. Results from the studies above cannot be transferred to an arbitrary vial.
Reading the next NAD+ headline
A proposed checklist for the next anti-aging claim, built from these three papers: ask which rung moved, since a doubled NAD+ level, an improved clamp measurement and a cognition score answer different questions; ask who was studied, because postmenopausal women with prediabetes and adults with amnestic MCI are different populations; ask whether a positive-sounding exploratory finding was the primary endpoint or a hypothesis for later; and ask how long the trial ran, since twelve weeks cannot speak to changes that unfold over decades.
None of this makes NAD+ biology uninteresting. The findings support distinct next questions: whether the metabolic effect extends to other populations, whether preliminary vascular signals hold up, and whether longer studies confirm a regional blood-flow effect. These three trials do not establish that raising NAD+ reverses human aging. That claim requires appropriate outcome evidence beyond the results reviewed here.
This article is based on the original published abstracts of the three trials; full texts were not reviewed, so details available only in the complete papers, such as exact dosing, subgroup results and adverse-event tables, are beyond its scope.
Sources and further reading
- Chronic nicotinamide riboside supplementation is well-tolerated and elevates NAD+ in healthy middle-aged and older adults. — original published abstract
- Nicotinamide mononucleotide increases muscle insulin sensitivity in prediabetic women. — original published abstract
- A phase-II randomized controlled pilot study of nicotinamide riboside supplementation in older adults with amnestic mild cognitive impairment. — original published abstract