NMN for 24 weeks lifted blood NAD+ in older adults, but hearing and fitness tests did not improve

A new trial in older adults found that taking a high dose of NMN every day for 24 weeks reliably raised markers of NAD+ in the blood. It did not, however, improve hearing or physical performance compared with placebo. The paper was published in npj Aging on September 25, 2026.

What the researchers did

NMN (nicotinamide mononucleotide) is a building block the body can use to make NAD+, a molecule cells use in many everyday chemical reactions. Studies in animals have suggested that raising NAD+ could help with age-related problems, but the authors note that human data are limited.

A team led from the University of Tokyo ran a randomized, double-blind, placebo-controlled trial. That means people were assigned by chance to NMN or a placebo (an inactive look-alike), and neither they nor the researchers knew who got which. Participants were aged 65 or over and took 1,250 mg of NMN once a day for 24 weeks. According to the trial registry entry (jRCT, registered October 2022), the dose was five 250 mg tablets, the main outcome was a change in hearing ability, and the target was 62 people. Secondary outcomes included physical function, blood tests and a six-minute walk test.

What they found

• Blood NAD+ went up. Analysis of whole blood showed that NMN significantly raised NAD+ and related substances.
• No clear gain on the main outcome. There was no significant improvement in hearing (auditory function).
• No clear gain in physical performance. The physical performance measures did not improve significantly either.
• Some small signals disappeared under strict testing. Changes in body composition, blood-fat measures and eating behavior appeared at first, but did not hold up once the researchers corrected for the many comparisons they made. The authors say these should be treated as exploratory.
• Tolerability. The high dose was generally well tolerated, with no significant adverse effects reported, though the authors say careful safety monitoring is still warranted.

The authors sum it up as: long-term high-dose NMN “robustly increases” circulating NAD-related substances, “whereas evidence for broader physiological benefit remains limited”. We read only the abstract and supporting pages of the paper, so we cannot give you exact group sizes or effect sizes.

What this means for you

What this means for you

• What was studied: 1,250 mg of NMN a day for 24 weeks. The authors describe this as a high dose.
• Who was studied: healthy adults aged 65 and over in Japan.
• What it shows: NMN can raise NAD+ levels in the blood. Higher NAD+ on a test is not the same as feeling or functioning better, and in this trial the hearing and fitness measures did not improve.
• Evidence strength (our simple scale: very low, low, moderate, high): low, for any benefit beyond raising blood levels. This is one trial.
• Read more in our beginner’s guide to NMN.

How strong is this evidence?

This is a proper randomized, placebo-controlled trial in humans, which is the right design for this question. But it was probably small (the registry target was 62 people, and we have not seen the final numbers), it lasted only 24 weeks, and it tested a single high dose in older adults, so it may not apply to younger people or other doses. The study was funded by MIRAILAB BIOSCIENCE Inc., which also supplied the NMN. Three authors are employees of the company, one of whom is its CEO. The company states it was not involved in the study design, data collection, analysis, interpretation or the decision to publish.

Sources

• Igarashi M, Naruse K, Takaoka Y, 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, published September 25, 2026. DOI: 10.1038/s41514-026-00482-7 (abstract, funding and competing-interest statements read; full results text was not available to us)
• Trial registry entry: jRCT jRCTs031220373

This article is for information only and is not medical advice. Speak to a healthcare professional before changing medication or supplements.