NAD+, NR and NMN: the longevity supplement debate, without the shortcuts

Reader questions answered

What is NAD+, and how do NR and NMN relate to it?

NAD+ is a coenzyme: a molecule that helps other molecules do their work. It participates in cellular energy metabolism and is consumed by enzymes involved in processes including DNA repair. Nicotinamide riboside (NR) and nicotinamide mononucleotide (NMN) are vitamin-B3-related precursors that can contribute to the body’s production of NAD+.

The proponents’ case starts with that biology. If NAD-related processes matter to cell function, perhaps increasing the supply of precursors could help address dysfunction associated with aging. A systematic review of human intervention studies found reliable increases in NAD-related biomarkers, alongside mixed results for metabolic, vascular and performance outcomes.

The sceptical response is not that the biology is imaginary. It is that a higher blood marker does not, on its own, show that the relevant tissues work better, that someone feels better or that they will live longer. How sustained changes in different tissues relate to clinical outcomes remains uncertain. The review searched studies through October 2025, so it does not capture the later trials discussed below.

Do human trials show benefits beyond blood-marker changes?

Some trials have measured more than blood markers, and proponents have results worth discussing. But the findings are specific to their populations and outcomes—not proof of a general anti-aging effect.

In the NICE trial, 90 adults with peripheral artery disease were assigned to NR, NR plus resveratrol, or placebo. After six months, the NR-only group’s change in six-minute walking distance was 17.6 metres greater than placebo’s. The combination did not significantly improve the primary outcome. That is a potentially meaningful functional signal, but it needs replication: the NR-only result had a reported P value of 0.08 under a prespecified one-sided threshold of 0.10. The publisher’s correction restored an omitted clinical-trial registration number (NCT03743636) in the abstract; it did not report changes to the trial’s walking-distance results.

In a placebo-controlled NMN trial, 25 postmenopausal women with prediabetes and overweight or obesity were studied for 10 weeks. The researchers reported improved muscle insulin sensitivity, but not improvements in fasting glucose or several liver and adipose measures. Muscle insulin sensitivity is a physiological outcome, not a demonstration that NMN prevents diabetes.

A later placebo-controlled NMN study in adults aged 65 or older found higher blood NAD-related metabolites after 24 weeks, but no significant improvement in its primary hearing endpoint or physical performance. Exploratory findings did not survive correction for multiple testing. Its sample size could not be reliably verified from the available early publication and is not supplied here.

Finally, the NOPARK randomized trial assigned 410 adults with early Parkinson disease to NR or placebo; 393 were included in the primary analysis. At 52 weeks, the adjusted symptom-score difference was 2.72 points in favour of placebo, and nonmotor symptoms worsened more with NR. The average difference was smaller than the trial’s stated threshold for clinically important worsening. This result does not establish what NR does in healthy adults, but it is a serious counterpoint to claims that raising NAD necessarily improves health.

Together, these trials show why both blanket enthusiasm and blanket dismissal go too far. A finding in peripheral artery disease cannot establish a benefit for everyone; a Parkinson’s result cannot settle every potential use. None of these results proves a longer life.

What do sceptical researchers actually question?

The central objection is the leap from a plausible mechanism to a promise. In an interview about NAD supplements, researcher Charles Brenner emphasized the importance of NAD biology while cautioning against calling NR, NMN or NAD+ proven longevity drugs. That distinction matters: studying a pathway is not the same as proving that changing it produces a useful outcome.

Sceptics also question whether changes in blood reflect changes where they matter, whether small findings can be reproduced and whether a chosen analysis makes a result appear more decisive than it is. Brenner published a methodological comment on the NMN insulin-sensitivity study, raising concerns including baseline imbalance and interpretation. A scientific comment is not a retraction, nor does it prove NMN cannot work.

His perspective also has an interest attached: Brenner has disclosed NR-related intellectual-property interests. That is relevant when reading criticism of a competing precursor, just as commercial interests are relevant when reading positive claims. The argument still has to be assessed on its merits.

Who funds the studies, and why does that matter?

Follow both money and materials. The older-adult NMN study was funded and supplied by MIRAILAB BIOSCIENCE; several authors were company employees and one was an executive. Its negative functional findings are a useful reminder that company funding does not automatically determine the direction of a result.

The NOPARK investigators’ university reports Norwegian public and foundation funding, with ChromaDex supplying NR and placebo. It says funders had no role in study conduct or publication decisions; that institutional statement is not independent verification of every aspect of conduct.

The NICE peripheral artery disease trial was funded by the American Heart Association; ChromaDex supplied NR and ReserveAge supplied resveratrol. Such relationships warrant scrutiny of trial design, analysis, reporting and replication. They do not, by themselves, invalidate a study. Equally, a trial of a compound does not establish that every retail brand contains what its label says or reproduces that trial’s result. The dossier provides no brand-specific proof on which to recommend a product.

What is known—and unknown—about safety?

Short trials can detect some problems, but they cannot establish the safety of taking a supplement for years. In the NICE trial, diarrhoea was reported by 39.3% of participants receiving NR alone, 54.6% receiving NR plus resveratrol and 27.6% receiving placebo. Reports do not prove the supplements caused each episode, and small groups make these estimates imprecise.

In NOPARK, serious adverse events occurred in 17 of 205 participants receiving NR and 29 of 205 receiving placebo. That numerical difference does not establish that NR prevented serious events; nor does it prove NR caused them. The worse average Parkinson symptom scores are a separate concern.

Rare effects, medicine interactions, pregnancy and breastfeeding, and consequences of long-term use remain insufficiently characterized. People managing a medical condition, taking medicines, pregnant or breastfeeding should discuss a supplement with a clinician rather than assume a short trial applies to them.

There is also a distinct issue with injections: the US FDA has warned about use of food-grade NAD+ to prepare sterile compounded products. That warning is not evidence that oral NR or NMN has the same risk; it concerns the suitability of ingredients for sterile preparations.

How does legal status differ across markets?

Availability on a website is not proof that a product is lawful or effective. Rules also differ by ingredient and product category.

• Australia: The Therapeutic Goods Administration says NMN may be used in listed medicines under specific restrictions, including oral use, adults only, a maximum of 500 mg daily and no more than 12 weeks. Sponsor restrictions also apply. The same update says NAD, NAD+ and NADH are not permitted ingredients in listed medicines. Permission under conditions is not proof of effectiveness or blanket authorization of every product.
• United States: FDA correspondence documents the history of its NMN dietary-ingredient and drug-exclusion review. The material available here does not confidently establish the final current position, so an earlier objection should not be presented as a definitive current ban.
• United Kingdom: The regulated-product register records a beta-NMN novel-food application. An application is not an authorization; the record alone does not settle the status of every product.
• New Zealand: Medsafe describes a framework in which it administers dietary-supplement regulations and MPI administers the Food Act. That general description does not establish ingredient-specific permission for a particular NR or NMN formulation.

Check the current official position for the precise ingredient and product before purchase. NR’s status across these markets and ingredient-specific New Zealand eligibility were not verified here.

What evidence would materially change the assessment?

The strongest case would come from adequately powered, preregistered, placebo-controlled trials that independent groups can replicate. They should measure outcomes people care about—such as mobility, disease incidence, quality of life or survival—alongside adverse effects and, where feasible, NAD changes in relevant tissues.

For example, independent confirmation of the NICE walking result using conventional statistical thresholds would make the case for that particular population more persuasive. Repeated well-powered null or adverse results would weaken claims in the populations studied. Longer follow-up could also clarify whether any short-term benefit persists and whether harms emerge.

Different precursors, doses and populations may produce different answers. But a rise in a biomarker, a registered trial or a company testimonial is not a substitute for a completed clinical outcome study.

What can I do instead of buying a costly supplement?

First, decide what you want the purchase to accomplish. If the goal is help with walking, metabolic health or a diagnosed condition, discuss that specific goal with a clinician rather than treating a general longevity claim as a treatment plan. The studies above do not establish that NR or NMN prevents disease or extends life, and the systematic review found mixed clinical results despite biomarker increases.

A reasonable alternative is to keep the money for care or activities tailored to your own health priorities, or simply wait for better evidence. If you still choose a supplement, ask what outcome you expect, how you will assess it, whether it could interact with your treatment and whether the exact product is permitted where you live. No verified retail price or product-specific quality assessment was supplied for this article, so we cannot calculate a meaningful cost comparison or endorse a brand.

Sources and conflicts

This article draws on the linked primary trials, a systematic review, an attributed interview and official regulatory or institutional sources. The research dossier was not independently fact-checked, and its search was not exhaustive. The NICE publisher correction (12 August 2024) was an omitted clinical-trial registration number in the abstract, not a reported change to walking results; the older-adult NMN study’s sample size could not be verified. Company funding and product supply, as well as Brenner’s NR-related intellectual-property interests, are disclosed above. These relationships are reasons for scrutiny, not automatic proof that findings are wrong.