| Summary: | Nicotinamide, nicotinic acid and nicotinamide riboside are vitamin B3 precursors of NAD<sup>+</sup> in the human diet. NAD<sup>+</sup> has a fundamental importance for cellular biology, that derives from its essential role as a cofactor of various metabolic redox reactions, as well as an obligate co-substrate for NAD<sup>+</sup>-consuming enzymes which are involved in many fundamental cellular processes including aging/longevity. During aging, a systemic decrease in NAD<sup>+</sup> levels takes place, exposing the organism to the risk of a progressive inefficiency of those processes in which NAD<sup>+</sup> is required and, consequently, contributing to the age-associated physiological/functional decline. In this context, dietary supplementation with NAD<sup>+</sup> precursors is considered a promising strategy to prevent NAD<sup>+</sup> decrease and attenuate in such a way several metabolic defects common to the aging process. The metabolism of NAD<sup>+</sup> precursors and its impact on cell longevity have benefited greatly from studies performed in the yeast <i>Saccharomyces cerevisiae</i>, which is one of the most established model systems used to study the aging processes of both proliferating (replicative aging) and non-proliferating cells (chronological aging). In this review we summarize important aspects of the role played by nicotinamide, nicotinic acid and nicotinamide riboside in NAD<sup>+</sup> metabolism and how each of these NAD<sup>+</sup> precursors contribute to the different aspects that influence both replicative and chronological aging. Taken as a whole, the findings provided by the studies carried out in <i>S. cerevisiae</i> are informative for the understanding of the complex dynamic flexibility of NAD<sup>+</sup> metabolism, which is essential for the maintenance of cellular fitness and for the development of dietary supplements based on NAD<sup>+</sup> precursors.
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