Nicotinamide Adenine Dinucleotide (NAD) is a coenzyme found in all living cells. It plays a crucial role in energy metabolism by helping convert food into energy. NAD exists in two forms: NAD+ (oxidized) and NADH (reduced), which participate in various biochemical reactions, including those involved in cellular respiration. In addition to energy production, NAD is important for DNA repair and maintaining cellular health. It is also involved in regulating sirtuins, a group of proteins that influence aging and stress responses. Due to its essential functions, NAD has gained attention in research related to aging and metabolic disorders.