NAD+ and the muscle result
Improved muscle insulin sensitivity came with unchanged body composition and HbA1c. The result becomes more useful when those measurements stay separate.
The women’s trial
The NMN trial in postmenopausal women with prediabetes earns the longest look from me. After 10 weeks, muscle responded better to insulin, while body composition and HbA1c stayed unchanged. NMN also changed insulin signaling in muscle. This was a particular response in a particular group of women.
There is room to be impressed here. Muscle insulin sensitivity is a meaningful physiological measurement, and the study went beyond asking whether a blood NAD+ value rose. The unchanged results narrow the claim: this experiment did not demonstrate weight loss, a change in muscle mass or a lower HbA1c.
I’m equally intrigued by the unchanged measurements. They tell us how selective the response was. Claims of generally better metabolism become much harder to defend once the individual measurements are named.
The precursor names
NAD+ is a coenzyme, a small molecule that helps enzymes carry out chemical reactions. It works with its related form NADH to handle electrons during energy metabolism, and it is consumed in other cellular work, including DNA repair and signaling. The review of NAD+ metabolism and aging explains those overlapping roles.
NMN and NR supply material for making NAD+. The human pill studies here chiefly tested these precursors. They were testing different substances from NAD+ itself, and a pill and an infusion introduce further differences in delivery. NAD+ also sits outside the peptide category despite the company it often keeps in wellness discussions.
The biology is busy enough without assigning it a universal benefit. In mice, deleting the NAD+-consuming enzyme CD38 preserved NAD+ levels and mitochondrial function with age. That genetic experiment helps explain a mechanism. A supplement claim still needs its own human outcome.
Walking and blood measurements
Another NMN trial, in healthy middle-aged adults, reported higher blood NAD+, better walking distance and improved quality-of-life scores compared with placebo. Those results offer a different assortment from the trial in women with prediabetes. The populations and measurements differ, so the papers cannot be combined into a single picture of a person whose every outcome improved.
In an NR trial lasting 8 weeks, healthy overweight adults had a dose-dependent rise in whole-blood NAD+, with no significant adverse-event difference from placebo. That is useful evidence about the blood response and tolerability during the study.
I have less appetite for a big blood number than for a useful functional change. The 2025 review of human precursor trials found limited clinical efficacy and sparse information about NAD+ dynamics inside particular human tissues. Blood is an accessible sample; a claim about an organ or about longer life needs evidence at that destination.
Injections and lasting safety
Pharmacy-prepared NAD+ shots and infusions lack drug approval and proven aging benefits. Preparation can introduce contamination and bacterial-endotoxin risks. Those product-quality questions sit alongside the biological questions, and oral precursor trials cannot settle them.
Short trials leave repeated use over years uncertain. NAD+ supports normal cellular activity and can also support growing cancer cells; its roles in cancer depend on context. The broader NAD+ biology review gives that cellular context, without establishing the safety of a wellness product for an individual.
A link between a particular tissue change and a lasting functional benefit would excite me more, especially if the study tracked harm carefully. The comparison of outcomes sets out what has actually been measured so far. Neither a higher blood value nor the muscle trial establishes extra healthy years.