Mitochondrial science
NAD+ precursors raise the marker. The function is the open question.
Twenty-five randomised trials establish that oral dosing works pharmacologically. Whether that produces something people notice remains unresolved.
Nicotinamide riboside and nicotinamide mononucleotide do what they say on the mechanism level. They reliably raise NAD+ related biomarkers in humans. What follows from that is where the argument sits.
The short version
- A 2026 review identified about 25 unique randomised NR or NMN trials involving roughly 1,070 participants, plus six systematic reviews or meta-analyses.
- Oral dosing consistently increases NAD+ related biomarkers, which is a robust pharmacodynamic finding.
- Functional benefits in healthy adults have been inconsistent across trials.
- The same review concluded that these compounds should not be treated as equivalent to urolithin A or spermidine, because their evidence profiles differ substantially.
A clean pharmacodynamic result
Very few supplements can demonstrate that they reach the target and move the intended biochemistry in humans. NAD+ precursors can. Across a large number of randomised trials, oral administration raises circulating NAD+ and related metabolites in a dose-responsive way.
That is genuinely more than most of this category can claim, and it deserves acknowledgement before the criticism.
Why the functional picture stayed murky
Several things complicate translation. NAD+ is a cofactor used in many processes, so raising the pool does not direct it toward any particular one. Blood levels may not reflect concentrations inside the tissues that matter. And in a healthy adult, the pathway may not be the limiting step at all.
Trial design compounds this. Endpoints have varied widely across studies, durations are mostly short, populations differ, and many studies are small enough that a modest true effect would be missed. Inconsistency of that kind does not prove absence of effect; it means the question is still open after 25 trials, which is itself informative.
This is one of the cleanest pharmacodynamic results in the supplement world, attached to one of its least settled clinical questions.
Velmixa Review
The comparison people actually want
The 2026 review's conclusion was blunt: current human evidence does not support treating urolithin A, spermidine, and NAD+ precursors as equivalent interventions. They differ in mechanism, in clinical evidence, and in translational maturity.
In practice that means NAD+ precursors have the most trials and the least resolved functional story, urolithin A has fewer trials and a more coherent one, and spermidine has the strongest observational signal and the least confirmatory data. Three different situations, sold on the same shelf under the same heading.
Reading the evidence
Oral NR and NMN raise NAD+ related biomarkers in humans, reproducibly, across many randomised trials. Short-term tolerability appears good.
Whether the biomarker change produces measurable improvements in strength, cognition, or cardiometabolic risk in healthy adults. Trials disagree.
Larger trials with pre-specified functional endpoints, longer durations, and populations where the pathway is plausibly limiting rather than healthy young volunteers.
Common questions
NR or NMN?
Both raise NAD+ related markers. There is no compelling human evidence that one is functionally superior, despite confident marketing on both sides.
Does an unresolved functional question mean it does nothing?
No. It means the trials so far have not settled it. Absence of a consistent finding and evidence of absence are different things, and both are different from a demonstrated benefit.
Sources
- Comparative narrative review of urolithin A, spermidine and NAD+ precursors — https://doi.org/10.4236/jbm.2026.145031
- Comparative review, ResearchGate record — https://www.researchgate.net/publication/405398243_Urolithin_A_Spermidine_and_NAD_Precursors_in_Human_Healthy_Aging_A_Comparative_Narrative_Review_of_Recent_Clinical_Evidence
- Longevity supplement trends: what's backed by science in 2026 — https://thelongevitystore.com/blogs/blog/longevity-supplement-trends-whats-backed-by-science-in-2026