NAD, or Nicotinamide Adenine Dinucleotide, 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 also acts as a signaling molecule, influencing processes like aging and stress responses. Research into NAD and its precursors, such as Nicotinamide Riboside, is ongoing, with potential implications for health and longevity.