In older male mice, taking a supplement called NMN every day for a year helped their bodies respond better to insulin — a hormone that controls blood sugar — even if their weight didn’t change.

What we've found so far suggests that long-term NMN supplementation may improve insulin sensitivity in aging mice, even without changes in body weight. Our analysis of the available evidence currently includes one assertion based on a study in older male mice. In this study, daily NMN supplementation over a 12-month period was linked to better insulin response, meaning the mice’s bodies were more effective at using insulin to regulate blood sugar [1]. Notably, this improvement occurred independently of body weight, suggesting the effect may not be tied to changes in fat or muscle mass [1]. What we’ve reviewed so far does not indicate any studies showing the opposite result. However, our current analysis is based on a single line of evidence from one study. While the finding is consistent and clear within this context, we don’t yet have enough data to know how reproducible or broad this effect might be. We don’t know if similar results would occur in female mice, younger mice, or in other species, including humans. The evidence we’ve reviewed leans toward a positive effect of long-term NMN use on insulin sensitivity in aging male mice, regardless of weight [1]. Still, because only one assertion is available, our understanding is limited at this stage. As we continue to analyze new research, our view may evolve. For now, what we can say is that in one study, older male mice responded to a year of NMN supplementation with improved insulin function, even without weight change. Practical takeaway: In mice, long-term NMN might help with blood sugar control as they age — not because they lose weight, but because their bodies handle insulin better. But one study isn’t enough to treat this as a settled conclusion.