Nicotinamide Adenine Dinucleotide (NAD+) is a fundamental redox coenzyme present in all living cells, serving as an essential electron carrier in mitochondrial respiration and a critical substrate for multiple longevity-associated enzymes including sirtuins, PARPs, and CD38. NAD+ research focuses on its central role in cellular bioenergetics, DNA repair mechanisms, epigenetic regulation, and age-related metabolic decline. As cellular NAD+ levels decrease with aging and metabolic stress, understanding NAD+ biology provides crucial insights into mitochondrial function, metabolic health, and interventions targeting age-related diseases.