NAD is a coenzyme found in all living cells that plays a crucial role in promoting health and prolonging lifespan. It has two forms, NAD+ and NADH, with NAD+ being the active form. Scientists have been studying NAD+ since the early 1900s, but only recently have begun to understand its full potential. NAD+ acts as a helper molecule by binding to other enzymes in the body, such as sirtuins, which require it to function properly. It is now being investigated for its potential in maintaining healthy organs and neurological systems in human patients.