That’s because Shin-ichiro Imai and Lenny Guarente showed that NAD acts as fuel for sirtuins. Without sufficient NAD, the sirtuins don’t work efficiently: they can’t remove the acetyl groups from histones, they can’t silence genes, and they can’t extend lifespan. And we sure wouldn’t have seen the lifespan-extending impact of the activator resveratrol. We and others also noticed that NAD levels decrease with age throughout the body, in the brain, blood, muscle, immune cells, pancreas, skin, and even the endothelial cells that coat the inside of microscopic blood vessels.
