In mice, when they take NMN or NR supplements by mouth, their muscles don’t turn these directly into NAD+—instead, the body first breaks them down into a form called nicotinamide and rebuilds them through a specific recycling process.

What we've found so far suggests that in mice, NMN and NR supplements are not directly converted into NAD+ in muscle tissue. Instead, the evidence we've reviewed indicates these compounds are first broken down into nicotinamide before being recycled back into NAD+ through a secondary pathway [1]. Our analysis of the available research shows that when mice take NMN or NR orally, the expected direct conversion to NAD+ in muscle does not appear to occur. Rather, the body seems to take a detour: breaking down these supplements into nicotinamide, a more basic form of vitamin B3, and then reassembling it into NAD+ using a salvage pathway [1]. This means the process may be less direct than commonly assumed. The evidence we've reviewed leans against the idea that NMN or NR boost muscle NAD+ through straightforward conversion. Nine out of the nine assertions we analyzed refute that direct transformation happens in mouse muscle [1]. While this doesn't rule out NAD+ increases altogether, it suggests the route is more complex and may involve intermediate steps in the liver or other tissues before NAD+ levels rise in muscle. We want to be clear: this is what we’ve found so far based on the limited evidence we’ve analyzed. There may be more to learn as new studies emerge, and our understanding could evolve over time. Practical takeaway: If you're thinking about NMN or NR supplements for muscle health in mice, the body may not use them the way you’d expect—instead of a straight path to NAD+, they take a longer, more roundabout route.