he effects of NR in humans is limited

But studies investigating NR supplementation in humans are in their infancy. Importantly, in humans, NR displays excellent safety and oral bioavailability — the extent a substance or drug becomes completely absorbed by the body for use. And studies have reported that NR supplementation can improve blood pressure, liver health, and physical function in the elderly, although the latter is not a consistent finding.

Despite the promising evidence in animals, several studies have reported no effect of chronic NR supplementation on metabolism, body composition, heart function, and endurance. On top of that, the effect of NR on mitochondrial biogenic signaling in human skeletal muscle following exercise remains unstudied. For these reasons, Stocks and colleagues investigated the effects of oral NR supplementation on whole-body NAD+ utilization and skeletal muscle mitochondrial signaling related to metabolism at rest and following endurance exercise in humans. 

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