In one small trial NMN improved how muscle handled insulin
Ten weeks of 250 mg a day raised insulin-stimulated glucose uptake into muscle in 25 postmenopausal women with prediabetes. It stands alone in the human literature.
What the study found
In 25 prediabetic women, NMN raised muscle insulin sensitivity
Ten weeks of 250 mg of NMN a day raised insulin-stimulated glucose uptake into muscle, measured by the clamp, the field's reference method, with matching changes in the muscle's own insulin-signalling proteins. It remains the one human trial that found NMN moving a hard metabolic endpoint.
The caveat · Women with prediabetes, at one site
Twenty-five postmenopausal women with prediabetes who were overweight or obese, at a single site, for ten weeks. The endpoint is insulin sensitivity, a metabolic measure, not an ageing or longevity one. The senior authors hold NMN patent-licensing interests through their university. Later pooled analyses of the wider NMN literature found no metabolic effect, in populations that were mostly not metabolically ill.
What we don't know
Whether NMN improved insulin handling in a 25-person trial is disputed: the women given it began with less than half the liver fat of those on placebo, and liver fat is something NMN is meant to act on. A trial that size cannot settle it.