NMN AND DISEASE: WHAT THE HUMAN TRIALS ACTUALLY SHOW

NMN (nicotinamide mononucleotide) has gone from longevity forums to Australian pharmacy shelves in under a year. In December 2025, the TGA added it to the permissible ingredients list for listed medicines, with conditions attached: oral use only, adults only, not in pregnancy or breastfeeding, a maximum of 500 mg a day, and 12 weeks of use or less.

That is a regulatory milestone. It is not a verdict on what NMN does in the body.

So here is the research, one disease area at a time, with the type of evidence and who was actually studied labelled in each section.

WHAT NMN ACTUALLY IS

NAD+ (nicotinamide adenine dinucleotide) is a coenzyme found in every cell. It shuttles electrons through energy production in the mitochondria, and it is the substrate consumed by three enzyme families: sirtuins (which regulate gene expression and metabolism), PARPs (which repair DNA) and CD38 (an enzyme tied to immune signalling and inflammation).

NAD+ itself is too large to be absorbed intact from the gut, so precursors are used instead. NMN sits one step upstream. In the salvage pathway, the enzyme NAMPT converts nicotinamide into NMN, and NMNAT then converts NMN into NAD+. Because NAMPT is the rate-limiting step, supplying NMN directly is designed to bypass the bottleneck.

The rationale is that NAD+ declines with age, which is well documented in animals. In humans, the decline across tissues is less consistent than the marketing suggests.

One finding is consistent. Every randomised human trial so far has found that NMN raises blood NAD+.

Whether that changes disease outcomes is a separate question, and the rest of this article is about that question.

METABOLIC HEALTH: INSULIN SENSITIVITY, GLUCOSE AND LIPIDS

Evidence type: randomised controlled trials and a meta-analysis
Who was studied: postmenopausal women with prediabetes and overweight or obesity, and mostly healthy middle-aged and older adults

The trial that launched NMN’s human reputation was published in Science in 2021. Twenty-five postmenopausal women with prediabetes took 250 mg of NMN a day, or placebo, for 10 weeks. Using the hyperinsulinaemic-euglycaemic clamp (the gold-standard measure of insulin sensitivity), the researchers found that insulin-stimulated glucose uptake into skeletal muscle improved, along with insulin signalling inside the muscle (AKT and mTOR phosphorylation).

What didn’t change matters just as much. Blood glucose, blood pressure, blood lipids, liver insulin sensitivity, liver fat and inflammatory markers all stayed the same. A published comment later raised a baseline difference in liver fat between groups; the authors responded that muscle insulin sensitivity, the primary outcome, was identical at baseline.

A 2023 trial took a much larger dose. Thirty overweight or obese adults aged 45 and over took 2,000 mg a day of a pharmaceutical-grade crystalline NMN (1,000 mg twice daily) for 28 days. Compared with placebo, body weight fell by about 1.9 kg, diastolic blood pressure by about 7 mmHg, and total and LDL cholesterol both dropped. That dose is four times the Australian daily maximum, and the trial ran for four weeks.

Then the pooled data. A 2024 systematic review and meta-analysis combined eight randomised trials, 342 adults, doses from 250 to 2,000 mg a day and durations from 14 days to 12 weeks. It found no significant effect on fasting glucose, fasting insulin, HbA1c, HOMA-IR or the lipid profile.

NAD+ goes up. Glucose, in the pooled data, does not.

The most defensible reading is that NMN’s metabolic effect, where it appears, is tissue-specific (skeletal muscle) and population-specific, not a general blood sugar intervention.

MUSCLE, WALKING AND PHYSICAL FUNCTION

Evidence type: small randomised controlled trials, mixed results
Who was studied: healthy older men, healthy middle-aged adults, amateur runners, and older men with diabetes and reduced physical function

This is NMN’s most consistent functional signal, and it is still modest.

In healthy men aged 65 and over, 250 mg a day for 12 weeks raised blood NAD+ and produced nominally significant improvements in gait speed and left-hand grip strength, with no change in muscle mass. The authors themselves noted the findings need validating in larger studies, and only a small number of participants completed the full 12 weeks.

In 80 healthy adults aged 40 to 65, doses of 300, 600 or 900 mg a day for 60 days all increased six-minute walking distance compared with placebo, with the longest distances at 600 and 900 mg. Blood NAD+ plateaued between 600 and 900 mg, suggesting a ceiling.

In 48 recreational runners training five to six times a week, 300, 600 or 1,200 mg a day for six weeks improved ventilatory threshold (a marker of how efficiently muscle uses oxygen) in the medium and high dose groups. VO2max did not change.

And in older men with diabetes who already had reduced grip strength or walking speed, 250 mg a day for 24 weeks was safe but did not improve either measure.

The people with the most to gain showed no measurable benefit.

That is the gap the research hasn’t closed yet. The positive results come mostly from healthy or already active people over short periods.

BLOOD VESSELS AND ARTERIAL STIFFNESS

Evidence type: animal studies and one randomised trial with a subgroup finding
Who was studied: old mice, and healthy middle-aged adults

In old mice, NMN restored endothelial function, reduced aortic stiffness and lowered vascular oxidative stress, with the effect running through SIRT1 activation in the arterial wall.

The human trial was smaller and less clear. Healthy middle-aged adults took 250 mg a day (125 mg twice daily) for 12 weeks. Pulse wave velocity, a measure of arterial stiffness, trended down in the NMN group but did not differ significantly from placebo overall. In subgroups with above-average BMI or blood glucose, the reduction did reach significance. Subgroup findings generate hypotheses. They don’t confirm them.

There is also a counterweight in the animal data. In ApoE knockout mice (bred to develop atherosclerosis), a 2025 study found that NMN and NR improved blood lipids and fatty liver but worsened arterial plaque over four months, with the effect dose-dependent and minimal at the lower dose tested. A separate 2025 study in the same mouse model found high-dose NR increased plaque and systemic inflammation, likely by shifting NAD+ consumption towards CD38 and PARP1. Yet a 2024 study in the same model found NMN reduced plaque.

The animal evidence points in both directions. For people with established cardiovascular disease, this is a genuinely open question.

THE BRAIN AND NEURODEGENERATION

Evidence type: almost entirely animal and cell studies
Who was studied: mouse and rat models of Alzheimer’s disease

In a mouse model of Alzheimer’s disease, NMN restored mitochondrial respiration in brain tissue. In rat models, it improved performance on memory tasks and reduced neuronal death. Mitochondrial dysfunction is a recognised feature of neurodegeneration, which is why NAD+ is a plausible target.

Plausible is not proven. The one small human NMN trial that assessed cognition, in healthy older men, did not show improvement. The early human trials in Parkinson’s disease and mild cognitive impairment that often appear in NMN marketing used NR, a different precursor.

HEART, KIDNEYS AND FERTILITY

Evidence type: animal studies, with human trials registered but not reported
Who was studied: mouse models of heart failure, kidney injury and reproductive ageing

Heart. In mouse models of pressure-overload heart failure and Friedreich’s ataxia cardiomyopathy, NMN preserved mitochondrial function and cardiac performance. Human heart failure trials to date have used NR. A Brigham and Women’s Hospital phase 2a trial is now registered to test oral NMN before coronary bypass surgery, measuring heart muscle NAD+ and markers of post-operative heart and kidney injury.

Kidneys. In mouse models of acute kidney injury (both reduced blood flow and chemotherapy-induced damage), NMN reduced tubular DNA damage, cellular senescence and inflammation, and lowered creatinine. A trial of pharmaceutical NMN in diabetic kidney disease is registered, with no results yet.

Fertility. This one has an Australian origin. Researchers at UNSW and the University of Queensland gave NMN to 14-month-old female mice for four weeks and restored egg quality, embryo development and live birth rates. The researchers were clear it has not been tested in human clinical trials, and Australian NMN products are not for use in pregnancy or breastfeeding.

WHERE NR GETS MISTAKEN FOR NMN

Much of what circulates as “NMN research” was done with nicotinamide riboside (NR), a closely related precursor that enters the NAD+ pathway one step earlier.

The 2025 Werner syndrome trial is a good example. Werner syndrome is a rare genetic disorder of accelerated ageing, and a randomised crossover trial published in Aging Cell found benefits for skin ulcers, cardiovascular markers and kidney function. The supplement was NR at 1,000 mg a day. The same applies to most of the human Parkinson’s and heart failure work.

Same pathway, different molecule, different trials. Evidence does not transfer automatically from one to the other.

WHAT WE STILL DON’T KNOW

Duration. Most human trials run four to 12 weeks. The TGA’s 12-week limit reflects how little long-term data exists.

Dose. Trials have used 250 to 2,000 mg a day. The higher-dose results cannot be assumed at the 500 mg Australian ceiling.

Who responds. A follow-up analysis of the 80-person walking trial found wide individual variation in how much blood NAD+ rose, and the size of that rise tracked improvements in walking distance and quality of life. Some people barely respond.

Which tissue. Trials measure NAD+ in blood. The effects that matter happen in muscle, liver, brain and blood vessels, and blood is an imperfect proxy for any of them.

Existing disease. NAD+ feeds sirtuins, but it also feeds CD38 and PARP-driven inflammatory pathways. Whether raising it helps or hinders in people with established atherosclerosis or other active disease has not been tested in humans.

THE BOTTOM LINE

NMN reliably moves a biomarker. It has not yet reliably moved a disease.

The strongest human signals are in skeletal muscle: insulin sensitivity in one well-designed trial, and walking and aerobic measures across several small ones. The metabolic pooled data is null. Cardiovascular, brain, kidney and fertility findings remain largely in animals, and some of the animal data points the wrong way.

The individual variation is the most interesting finding of all. If two people take the same dose and only one of them shows a meaningful rise in NAD+, the question was never just “does NMN work?”

It was always “does it work for you?”

REFERENCES

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Bertoldo MJ, Listijono DR, Ho WHJ, et al. NAD+ repletion rescues female fertility during reproductive aging. Cell Rep. 2020;30(6):1670-1681. doi:10.1016/j.celrep.2020.01.058

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