Popularity is not equal quality
Many learn about NAD+ in our cellular metabolism and how it decreases with age from the book Lifespan by David Sinclair. In it, he promotes NMN, an anti-aging supplement that can boost NAD+ to youthful levels. As such, NMN is by far the most popular NAD+ booster. However, it is not the only one. There is also NR and Niacin (Vitamin B3). Of the three, NMN is actually the one with the worst bioavailability and the least amount of science to support it.