NMN supplement marketed as anti-ageing faces cautious scrutiny from scientists

NMN, or nicotinamide mononucleotide, has moved from research labs to high street shelves, with retailers advertising it as a daily supplement that can boost energy, metabolism and even brain health. Proponents say NMN helps maintain levels of NAD, a molecule essential for cellular function, and that NMN converts into NAD in the body. They point to prices as low as £34 for 30 capsules — roughly £1 a day — with products sold in Boots and other outlets. In theory, NMN is meant to counteract age-related NAD declines that occur as people grow older, a decline researchers say can influence how cells repair DNA, produce energy and respond to stress.

Some doctors have publicly suggested that NMN can “knock years off” a person’s age, and high-profile advocates, including biohacker Bryan Johnson, have incorporated NMN into their anti-ageing regimens. Johnson, 47, has been cited as an example of how some individuals pursue longevity strategies that include NMN. In the medical literature, however, the consensus remains cautious: much of the strongest evidence to date comes from animal studies or short-term human trials, and experts warn that results in mice do not always translate to humans.

In biological terms, NAD is a coenzyme that powers a family of genes tied to ageing. The NAD pool in the human body tends to shrink by about half with advancing age, a change that researchers say may undermine DNA repair, energy production and metabolic resilience. NMN is studied because it potentially sustains NAD levels as people age and NAD-dependent processes begin to falter. Advocates contend that maintaining NAD levels could support cellular repair and longevity pathways, while critics stress that the existing human data are preliminary and that long-term safety at higher doses have not been established.

Harvard Medical School genetics professor David Sinclair, a leading voice in ageing research and co-author of Lifespan: Why We Age—and Why We Don’t Have To, has described NMN as a promising avenue for anti-ageing. In animal studies, Sinclair’s group has shown that feeding ageing mice NMN can restore cellular features to resemble those of younger animals, including muscle function, with no adverse short-term effects reported in those experiments. Yet Sinclair has also cautioned that positive findings in mice often do not replicate in humans, and he emphasizes the need for long-range human trials to determine safety and efficacy.

Other scientists urge caution. Dr Cathy Slack, an associate professor at the University of Warwick who focuses on the biology of ageing, notes that most human data come from small studies or early-stage trials. She said longer, larger trials are needed to determine whether NMN supplementation at the doses used in consumer products is safe and beneficial over years of use. Dr Leonard Josipovic, a plastic surgeon and supplement specialist, has described mixed early feedback from patients who report more energy and greater mental sharpness, but he adds that these observations are not definitive evidence of anti-ageing and that expectations should remain measured.

Clinical trials in humans are ongoing, with many exploring doses ranging from several hundred milligrams to around 1,000 milligrams per day. Consumer products commonly stock 250 milligram capsules, and manufacturers often target adults who are in good health. In recent years, some smaller studies have produced hints of benefit: a 2021 trial involving 48 young and middle-aged runners reported improved aerobic capacity with high-dose NMN over six weeks; a 2022 study published in Nutrients noted increased muscle responsiveness but also some drowsiness among older participants taking NMN; a 2023 review of ongoing human clinical trials concluded that while NMN is gaining popularity, researchers need longer, better-designed studies to assess safe dosing, tolerance and frequency. The overall takeaway remains that NMN shows potential but is not a proven “fountain of youth,” and health professionals urge that people consider traditional aging-prevention strategies as the foundation of wellbeing—adequate sleep, regular exercise and a nutrient-rich diet.

As with many emerging supplements, regulators and clinicians stress that NMN should not be viewed as a guaranteed solution to ageing. While proponents highlight NMN’s role in supporting NAD-related pathways, independent experts emphasise that the safety profile over the long term still needs solid evidence, particularly at the higher doses sometimes used in animal research. For now, the mainstream medical position is cautious: NMN may offer potential cellular benefits for some individuals, but more robust human data are needed before broad recommendations can be made. In the meantime, health authorities continue to underscore that foundational health measures—sleep, activity and nutrition—remain the cornerstone of healthy ageing.