Nicotinamide Adenine Dinucleotide, or 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: oxidized (NAD⁺) and reduced (NADH), which participate in various biochemical reactions, including those involved in cellular respiration. In addition to its role in energy production, NAD is important for DNA repair and maintaining cellular health. It also acts as a signaling molecule, influencing processes such as aging and inflammation. Research into NAD has gained attention for its potential implications in health and longevity.