“NMN reverses aging”

NMN does one thing dependably. It raises NAD+ in the blood, and more of it at higher doses: among 80 healthy middle-aged adults taking 300, 600 or 900mg a day for 60 days, NAD+ rose in all three dose groups compared with placebo, highest in the two larger ones [2]. A 2026 study in Nature Metabolism of 65 healthy adults found NMN and nicotinamide riboside, a sister compound sold for the same purpose, lifted circulating NAD+ by much the same amount over a fortnight.

So the supplement does the biochemical job on the label. Whether that job buys anyone anything is the part that keeps coming back negative.

On the metabolic markers people buy it for, pooling the trials says no. A 2024 review in Current Diabetes Reports combined eight randomised trials covering 342 mostly non-diabetic middle-aged and older adults, at 250 to 2,000mg a day for two weeks to twelve, and found no benefit on fasting blood sugar, fasting insulin, glycated haemoglobin (a measure of average blood sugar over the previous three months), insulin resistance or cholesterol [1].

The physical-function results are messier:

• 80 middle-aged adults walked further in a six-minute test on 300, 600 and 900mg a day than on placebo [2]
• 60 older adults on 250mg a day for 12 weeks covered 4 metres faster than placebo and slept better, but the trial's own pre-chosen main measure, a stepping test, showed no difference at all [3]
• 108 older Japanese adults on 250mg for 12 weeks got better at standing up from a chair five times, and less drowsy in the daytime, with the clearest gains among those taking it in the afternoon (Nutrients, 2022)
• 48 amateur runners on 300 to 1,200mg a day for six weeks improved on some breathing measures during exercise, though VO2 max itself, the most oxygen the body can use while working hard, did not budge

Hold onto that second one. A trial that misses the measure it chose in advance and hits a secondary one has produced a hint, and hints are how this literature keeps presenting itself.

The sharpest test of whether raising NAD+ changes anything used the sister compound. A phase-two trial published in Alzheimer's & Dementia gave nicotinamide riboside to 42 older adults with mild memory impairment for 12 weeks: their blood NAD+ doubled and their cognition did not improve.

Mice do better, and mice are not people. In a 2025 Journal of Nutrition experiment, mice already 14 months old ate a high-fat diet for seven months with NMN in their water; it raised their NAD+, kept them more active and limited the muscle and kidney damage the diet otherwise did.

Who this evidence does not cover:

• anyone wanting an ageing result, because no trial has measured biological age, a body measurement reflecting how worn your cells are rather than how many birthdays you have had, or lifespan
• people with diabetes, largely excluded from the pooled trials [1]
• anyone taking it beyond 12 weeks, the longest any trial has run [1]

Safety reads reasonably at the doses tested. No trial found serious harm, and all 80 people in the dose-ranging trial completed 60 days at up to 900mg a day without one [1], [2], [3]. Two things stay open: long-term use is unstudied, and NAD+ is also used by cancer cells to grow, so what raising it means for someone carrying an undetected tumour is a question no trial has answered.