NAD+, or nicotinamide adenine dinucleotide, is a critical coenzyme found in every cell in your body, and it’s involved in hundreds of metabolic processes. But NAD+ levels decline with age. NAD+ has two general sets of reactions in the human body: helping turn nutrients into energy as a key player in metabolism and working as a helper molecule for proteins that regulate other cellular functions. Recently, NAD+ has become a prized molecule in scientific research because of its central role in biological functions.