NAD+ in Human Ageing: The 2025 Nature Metabolism Review, Updated for 2026

The 2025 Nature Metabolism review on NAD+ precursors reaches a narrower conclusion than most longevity marketing: human evidence remains sparse, tissue responses are poorly characterized, and clinical trials have shown limited efficacy.¹

The paper is a scholarly review, not a systematic review and not a trial. Its central contribution is a map of the translational gaps between ageing biology, blood measurements, tissue metabolism, and clinical outcomes.

Research published in 2026 adds several human signals. None overturns the review’s main caution or establishes routine NAD+ treatment for extending healthspan or lifespan.

Review note, August 28, 2026: WLC corrected the article type, removed prices and a false niacin-versus-infusion equivalence, and added three 2026 evidence updates. Route and purchasing questions remain in the separate IV versus oral NAD+ guide.

The review’s four conclusions

1. Age-related decline is not equally demonstrated across human tissues

NAD+ is essential to cellular metabolism, and animal studies often show age-related changes. In humans, however, a consistent age-related decline has been demonstrated in only a limited number of studies.¹

That does not mean decline never occurs. It means the size, tissue distribution, timing, and clinical meaning of the change remain uncertain.

2. Blood is not a universal proxy for tissue

Many trials measure whole blood, plasma metabolites, or peripheral blood cells. Those compartments are accessible, but they do not automatically represent skeletal muscle, liver, adipose tissue, or brain.

A blood NAD-related metabolite rising after supplementation can demonstrate exposure. It does not prove that the intended tissue changed or that the person functions better.

3. Rodent findings do not establish human benefit

Preclinical studies are useful for mechanisms and dose exploration. Human metabolism, disease, lifespan, and treatment context differ. The review warns against treating animal rejuvenation findings as established human therapy.¹

4. Human clinical efficacy is limited and heterogeneous

Trials vary by precursor, formulation, dose, duration, participant age, baseline disease, tissue, and endpoint. The result is not a single positive or negative verdict. It is an evidence base that does not yet support broad anti-ageing claims.

The evidence ladder the review exposes

NAD-related studies can answer different questions:

Level	Question	Example of evidence
1. Exposure	Did the compound or a related metabolite appear in blood?	Blood NAD metabolome
2. Tissue engagement	Did metabolism change in the target organ?	Muscle biopsy or organ-specific assay
3. Functional effect	Did a validated physiological measure improve?	Insulin sensitivity, strength, exercise capacity
4. Clinical effect	Did symptoms, disease events, disability, or hospitalization improve?	Prespecified patient outcome
5. Healthy-ageing effect	Did healthspan or survival improve?	Long-term controlled outcome data

Commercial explanations often move from level one to level five in one sentence. The review shows why that leap is unsupported.

What changed in 2026

Three publications are useful because they sit at different levels of the ladder.

NMN and blood pressure: a small outcome-specific signal

A 2026 systematic review and meta-analysis included 349 participants from 10 randomized trials. NMN was associated with a modest 2.15 mmHg reduction in diastolic blood pressure. The overall systolic-blood-pressure result was not statistically significant.²

This is more informative than a blood NAD measurement because blood pressure is a clinical risk factor. It is still a narrow result from small, heterogeneous trials. It does not demonstrate generalized rejuvenation, and subgroup findings need confirmation.

Commercial IV records: tolerability, not efficacy

A 2026 retrospective study compared records from clients who received four consecutive days of 500 mg IV NAD+ or IV nicotinamide riboside in a commercial setting. NAD+ recipients reported moderate to severe gastrointestinal symptoms, increased heart rate, and chest pressure during infusion. NR recipients reported milder tingling and cramping; symptoms resolved after infusion.³

The design was retrospective, non-randomized, without placebo, and limited to 30-day follow-up. Its main contribution is short-term tolerability information. Variable exploratory metabolic changes cannot establish a longevity benefit.

Ischemic heart failure: a disease-specific randomized signal

A single-center randomized trial enrolled 180 adults with heart failure caused by ischemic cardiomyopathy. Seven days of low-dose IV NAD+ were added to guideline-directed therapy. The study reported a greater improvement in left-ventricular ejection fraction at one month in the NAD+ group.⁴

This result belongs to a defined disease, dose, co-treatment, and endpoint. It cannot be generalized to high-dose commercial infusions in healthy adults. It does show why “NAD+ has no human evidence” would also be too broad.

What the review did not establish

The paper did not establish that:

• every adult has a clinically important NAD+ deficiency;
• one blood test can diagnose tissue-specific NAD+ depletion;
• NR, NMN, niacin, nicotinamide, IV NAD+, and IV NR are interchangeable;
• a blood increase predicts cognition, energy, muscle function, or disease prevention;
• niacin is clinically equivalent to an expensive infusion;
• a short-term biomarker change proves slower ageing;
• a specific commercial dose is effective or safe for long-term preventive use.

The previous WLC version made the niacin comparison too directly. Entering the same metabolic network is not evidence of head-to-head equivalence.

How to read a new NAD+ study

Record seven fields:

1. Molecule and route: NR, NMN, nicotinamide, niacin, NAD+, or another intervention.
2. Population: healthy adults, older adults, a deficiency group, or a specific disease.
3. Comparator: placebo, active comparator, usual care, or no control.
4. Target: blood exposure, tissue engagement, function, or clinical outcome.
5. Duration: hours, weeks, months, or years.
6. Magnitude: absolute change, confidence interval, and clinical relevance.
7. Transferability: whether the result applies to the product, dose, and person being discussed.

This prevents a disease-specific infusion trial from becoming a claim about wellness infusions, or a blood-metabolite trial from becoming a claim about lifespan.

A current evidence ledger

Claim	Current status	Reason
Some precursors raise blood NAD-related metabolites	Supported	Demonstrated in multiple human trials reviewed in 2025
Human NAD+ declines uniformly with age in all relevant tissues	Unsupported	Tissue data remain sparse and inconsistent
Oral NMN may have a small blood-pressure effect	Preliminary	2026 meta-analysis found a modest diastolic signal
Commercial IV NAD+ has established short-term tolerability	Partial	A small retrospective study recorded notable infusion symptoms
IV NAD+ improves ischemic heart-failure function	Preliminary, disease-specific	One single-center randomized trial reported an LVEF difference
NAD+ intervention improves healthy lifespan	Unsupported	No controlled human healthspan or survival evidence
A blood NAD result proves target-organ benefit	Unsupported	Exposure is not tissue engagement or clinical efficacy

Bottom line

The Nature Metabolism review remains a useful reference in 2026 because it does not reduce the field to hype or failure. It shows that the human NAD+ story is compartment-specific, intervention-specific, and outcome-specific.

The 2026 additions provide a modest NMN blood-pressure signal, commercial infusion tolerability data, and a disease-specific heart-failure result. They do not establish oral or IV NAD+ as a general longevity treatment.

The correct next question is always: which molecule changed what outcome, in which tissue and population, for how long?

Footnotes

1. Vinten APB, et al. NAD+ precursor supplementation in human ageing: clinical evidence and challenges. Nature Metabolism. 2025. doi:10.1038/s42255-025-01387-7. ↩ ↩² ↩³

2. Effects of Nicotinamide Mononucleotide Supplementation on Blood Pressure: A Systematic Review and Meta-Analysis of Randomized Controlled Trials. Nutrients. 2026. ↩

3. Intravenous infusion of NAD+ versus nicotinamide riboside: a retrospective tolerability pilot study in a real-world setting. Frontiers in Aging. 2026. ↩

4. Effect of Nicotinamide Adenine Dinucleotide on Heart Failure Caused by Ischemic Cardiomyopathy: A Randomized, Placebo-Controlled Trial. Cardiology and Therapy. 2026. ↩