NMN raises NAD⁺. In this study, it raised it substantially—about 3.6-fold. But what happened next was more interesting: hearing, grip strength, and walking performance did not improve.
To me, this study raises a question that matters beyond NMN itself:
Does changing a number associated with aging actually change aging?
Why did NMN attract attention as an anti-aging compound?
NMN stands for nicotinamide mononucleotide. It is one of the precursors in the metabolic pathways our bodies use to make NAD⁺.
NAD⁺ participates in cellular energy metabolism, DNA damage responses, and important processes involving sirtuins and PARPs. As studies reported declining NAD⁺ in various tissues during aging, an appealing hypothesis emerged:
- Aging → lower NAD⁺
- NMN supplementation → higher NAD⁺
- Therefore → slower aging
The reasoning sounds plausible. But I question that final arrow. An association between NAD⁺ and aging is very different from evidence that artificially raising NAD⁺ slows aging in humans.
Researchers tested high-dose NMN in people
The study was published in npj Aging in September 2026. Researchers randomly assigned 62 healthy Japanese adults aged 65 or older to NMN or placebo.
The NMN dose was 1,250 mg daily for 24 weeks. The trial was randomized, double-blind, and placebo-controlled; 60 participants were included in the final efficacy analysis.
The primary outcome was pure-tone hearing. Researchers also assessed real-world physical function, including grip strength, walking speed, the 30-second chair-stand test, and the six-minute walk test.
NAD⁺ clearly increased
This part was quite clear. Whole-blood NAD⁺ increased substantially in the NMN group compared with placebo. The researchers described an increase of approximately 3.6-fold, a statistically clear change.
Can NMN supplementation raise NAD⁺? On that question, we can answer “yes” with considerable confidence. The question is what comes next.
Did people function better?
There was no between-group difference in hearing, the trial’s primary outcome. Nor were there significant differences in grip strength, walking speed, the 30-second chair-stand test, or the six-minute walk test.
There were a few interesting signals, including an increase of about 0.8 kg in soft lean mass in the NMN group. However, the statistical significance disappeared after adjustment for testing multiple outcomes. The researchers classified these as exploratory findings, rather than established benefits.
Ultimately, the clearest change in this trial was a number: NAD⁺. The functional outcomes we hoped to improve did not show clear gains.
Why did higher NAD⁺ fail to translate into benefits?
We do not yet know. There are several possible explanations.
First, the measurement was whole-blood NAD⁺. A 3.6-fold rise in blood does not establish a comparable rise in muscle, brain, blood vessels, or the inner ear.
But I think there is a more fundamental question: is declining NAD⁺ really a cause of aging?
Suppose a substance decreases in aging tissue. At least two explanations are possible. Its decline might contribute to aging—or aging might cause its decline. In biology, the two processes can also influence one another.
Without distinguishing these possibilities, “NAD⁺ falls with age, so raising it makes us younger” contains a substantial logical leap.
Here is a deliberately stark analogy. Gray hair is strongly associated with aging. Dyeing it black does not make a person younger. We need to distinguish a marker that changes with aging from a cause that drives aging.
More is not necessarily better
The dose in this trial—1,250 mg daily—was substantial. NAD⁺ did increase markedly. Yet functional improvement was not demonstrated.
This result does not establish that high-dose NMN is harmful. It does, however, prompt a reasonable question: does a larger increase in NAD⁺ produce better outcomes in people?
Current human data do not justify answering “yes.” Most metabolic systems do not operate along a simple straight line. Even when a deficiency causes problems, continually pushing a substance above normal does not necessarily improve the outcome. Living organisms are systems of homeostasis.
I pay closer attention to clinical outcomes than laboratory numbers
NMN is not the only reason this study interests me. Similar claims recur throughout the anti-aging field:
- NAD⁺ increased.
- Epigenetic age fell by several years.
- Telomeres lengthened.
- Inflammatory markers decreased.
- A biological-age score improved.
These are all interesting findings. But we must ask one more question: did the person actually become healthier?
What we ultimately want from aging research is not a laboratory number. We want muscle and cognitive function to be preserved, cardiovascular disease and cancer to become less common, disability to arrive later, and—ultimately—more years lived in good health. Those are the outcomes that matter.
Does this mean NMN does not work?
That conclusion would also go too far. This trial involved about 60 people and lasted 24 weeks. Participants were relatively healthy older Japanese adults. Its sample size was calculated primarily to assess hearing changes; it was not designed to evaluate every aspect of human aging.
What we can say is this:
NMN can substantially increase NAD⁺ in humans. But human evidence that raising NAD⁺ translates into meaningful anti-aging benefits remains insufficient.
The study was supported by NMN manufacturer MIRAILAB BIOSCIENCE, and company employees were among the authors. That is not a reason to dismiss its findings. In fact, it is interesting that even this company-supported trial found a clear separation between a strong rise in NAD⁺ and functional benefits.
A younger number is not a younger person
NAD⁺ is an interesting molecule and deserves continued study. Meaningful effects may yet be found in specific patient groups or tissues, or with different doses and durations.
But given the current human evidence, I remain skeptical of treating an increase in NAD⁺ itself as proof that aging has been treated.
In this trial, NMN did its job very well. It raised NAD⁺—by an impressive 3.6-fold. That alone was not enough.
One of the biggest traps in the anti-aging field is confusing a change in an aging-related number with a change in aging itself.
In future NMN studies, I would like to see something more than higher NAD⁺ levels: better outcomes for people. Only when those benefits are demonstrated can we begin to call the increase a meaningful anti-aging effect.
Reference
Igarashi M, et al. Sustained NAD⁺ augmentation by high-dose nicotinamide mononucleotide supplementation in older adults: a 24-week randomized, double-blind, placebo-controlled trial. npj Aging. 2026. DOI: 10.1038/s41514-026-00482-7.
This article introduces and interprets scientific research. It is not an individual recommendation to take NMN.