The short version
- Oral NAD precursors reliably raise blood NAD: in 80 healthy middle-aged adults, NMN at 300, 600 or 900mg daily raised it significantly at both day 30 and day 60.
- Raising NAD in tissue is not the same as changing what the tissue does — in 12 aged men given 1g of nicotinamide riboside for 21 days, the muscle NAD metabolome rose but mitochondrial bioenergetics were unchanged.
- A 2025 systematic review of 12 NMN studies in 513 participants found a significant effect on blood NAD, no significant effect on most clinically relevant outcomes, and concluded that an exaggeration of the benefits may exist in the field.
- The strongest positive human NMN result is a 10-week trial in postmenopausal women with prediabetes, where insulin-stimulated glucose disposal increased on a hyperinsulinaemic-euglycaemic clamp.
- No human trial has shown that raising NAD extends healthy life; the dramatic ageing findings come from animal work.
Nearly everything thrilling that has ever been said about NAD+ happened in a mouse. That is not a dismissal — rodent work is how you find out where to look — but it is the single most important context for reading anything about NMN, and it is the context that gets stripped out first.
We sell NAD precursors. So here is the human literature, including the parts that argue against the purchase.
Start with what is solidly established
Oral NAD precursors raise NAD. This part is not in dispute and it has been shown repeatedly.
Martens and colleagues ran a 2 × 6-week randomised, double-blind, placebo-controlled crossover trial of nicotinamide riboside in healthy middle-aged and older adults, and found it well tolerated and effective at stimulating NAD+ metabolism. Yi and colleagues randomised 80 healthy middle-aged adults to placebo or 300, 600 or 900mg of NMN daily for 60 days; blood NAD rose significantly in every treated group at both day 30 and day 60 (all p ≤ 0.001), highest at 600 and 900mg, with no safety issues and good tolerability throughout.
If your question is "does the molecule get in and move the marker," the answer is yes. That is a genuine pharmacological result, and it is more than many supplement ingredients can claim.
The trial that shows why that isn't the same as working
Elhassan and colleagues gave 12 aged men 1g of nicotinamide riboside per day for 21 days in a placebo-controlled, randomised, double-blind crossover trial, and then took muscle biopsies.
The NAD+ metabolome in skeletal muscle went up — the compound reached the tissue and was being processed. RNA sequencing showed a gene expression signature suggesting downregulation of energy metabolism and mitochondrial pathways. And then the measurement that matters: mitochondrial bioenergetics were unchanged. Circulating inflammatory cytokines did fall.
Read that sequence carefully, because it is the crux of the entire field. Getting NAD into the tissue is not the same as making the tissue do anything differently. The whole longevity pitch rests on an inference between those two steps, and this trial is where the inference did not hold.
The best positive human result, stated precisely
Yoshino and colleagues ran a 10-week randomised, placebo-controlled, double-blind trial of NMN in postmenopausal women with prediabetes who were overweight or obese. Insulin-stimulated glucose disposal, measured with a hyperinsulinaemic-euglycaemic clamp — the reference method, not a proxy — increased after NMN and did not change on placebo. Skeletal muscle insulin signalling increased alongside it, and NMN upregulated genes related to muscle remodelling.
This is the strongest human NMN result there is, and it is worth respecting. It is also one small trial, in one narrowly defined group, on a mechanistic endpoint. It says NMN did something measurable to muscle insulin sensitivity in those women. It does not say anything about healthspan, lifespan, energy, or how a healthy 40-year-old will feel.
What happens when you pool the trials
A 2025 systematic review with meta-analysis screened 4,049 records and included 12 studies with 513 participants, looking at NMN's effect on fasting glucose, triglycerides, total cholesterol, LDL and HDL.
The pooled result: a significant effect on raising blood NAD, and most of the clinically relevant outcomes not significantly different from control. The risk-of-bias assessment is worth quoting on its own terms — seven studies raised "some concerns" and five were rated high risk. The authors' conclusion is unusually direct for a meta-analysis: their findings "suggest that an exaggeration of the benefits of NMN supplementation may exist in the field."
When a paper in your own product's literature says that, the correct response is to print it, not to bury it.
What about the "biological age" results?
The Yi trial also reported that walking distance on a six-minute walk test improved significantly versus placebo at days 30 and 60, that self-reported health on the SF-36 improved, and that "blood biological age" rose in placebo while staying flat in the treated groups.
Take those in order. The walk-test result is a real functional measure and the most interesting of the three. SF-36 is self-reported and unblinded expectations are hard to rule out. And the biological age figure came from an online calculator, which is not a validated clinical endpoint — it is a model fitted to routine bloods. Meanwhile, in the same trial, HOMA-IR showed no significant difference from placebo at day 60.
Where this leaves you
The honest summary: NAD precursors reliably raise NAD, are well tolerated at doses up to 900mg daily in the trials run so far, and have produced a handful of modest, mostly mechanistic human findings — some of which did not replicate as functional change. The dramatic ageing results are preclinical. Nobody has shown, in humans, that raising NAD extends healthy life.
That is a legitimate reason to be interested and a bad reason to be certain.
What we'd actually tell you
If you take one, take it for the biology you find interesting and hold the expectation loosely. Judge it over months, not weeks, and judge it against something concrete — training capacity, recovery between sessions — rather than a vague sense of vitality, which is exactly what an unblinded expectation will manufacture for you.
And keep the budget honest. Sleep, resistance training and adequate protein have vastly better human evidence for how you function at 60 than any NAD precursor currently does. If an NMN subscription is competing with any of those three for money or attention, the subscription should lose. We would rather sell you less and be right about it.
Good questions
Does NMN actually do anything you can feel?
Not reliably, on the human evidence so far. NMN dependably raises blood NAD, but a 2025 meta-analysis of 12 studies in 513 participants found most clinically relevant outcomes were not significantly different from control. Its authors wrote that an exaggeration of the benefits of NMN supplementation may exist in the field. We sell NAD precursors and would still rather you knew that.
How much NMN should I take, and is it safe?
Trials have used 300, 600 and 900mg daily for 60 days in healthy middle-aged adults, with good tolerability and no safety issues reported; blood NAD rose significantly at every dose and highest at 600 and 900mg. Nicotinamide riboside has also been well tolerated over six weeks in older adults. Longer-term human safety data does not yet exist.
Does NMN reverse your biological age?
No trial has shown that. One study reported a blood biological age score rising on placebo while staying flat on NMN, but that figure came from an online calculator fitted to routine bloods, not a validated clinical endpoint. In the same trial, HOMA-IR showed no significant difference from placebo at day 60. Treat the claim as marketing.
Is NMN or NR better?
Nobody has run the comparison that would answer that. Both raise NAD in humans: nicotinamide riboside in a six-week crossover trial in middle-aged and older adults, NMN across doses from 300 to 900mg. Choosing between them on current evidence is a preference, not a conclusion the literature supports. If a brand tells you one is clearly superior, ask which trial says so.
Does raising NAD actually change anything in your muscles?
Not in the one trial that looked directly. Twelve aged men took 1g of nicotinamide riboside daily for 21 days; muscle biopsies showed the NAD metabolome rose, confirming the compound reached the tissue, but mitochondrial bioenergetics were unchanged. Circulating inflammatory cytokines did fall. Getting NAD into a tissue is not the same as making that tissue behave differently.
Is an NMN subscription worth the money?
Only after the basics are paid for. Sleep, resistance training and adequate protein have vastly better human evidence for how you function at 60 than any NAD precursor currently does. If an NMN subscription is competing with any of those three for money or attention, the subscription should lose. We would rather sell you less and be right about it.
Sources
- Yoshino M, et al. Nicotinamide mononucleotide increases muscle insulin sensitivity in prediabetic women. Science, 2021. View study
- Elhassan YS, et al. Nicotinamide Riboside Augments the Aged Human Skeletal Muscle NAD+ Metabolome and Induces Transcriptomic and Anti-inflammatory Signatures. Cell Rep, 2019. View study
- Yi L, et al. The efficacy and safety of β-nicotinamide mononucleotide (NMN) supplementation in healthy middle-aged adults: a randomized, multicenter, double-blind, placebo-controlled, parallel-group, dose-dependent clinical trial. GeroScience, 2023. View study
- Martens CR, et al. Chronic nicotinamide riboside supplementation is well-tolerated and elevates NAD+ in healthy middle-aged and older adults. Nat Commun, 2018. View study
- Zhang J, et al. Efficacy of oral nicotinamide mononucleotide supplementation on glucose and lipid metabolism for adults: a systematic review with meta-analysis on randomized controlled trials. Crit Rev Food Sci Nutr, 2025. View study
These statements have not been evaluated by the Food and Drug Administration. This product is not intended to diagnose, treat, cure, or prevent any disease.
