NAD⁺ is a fundamental molecule in human life and health as it participates in energy metabolism, cell signalling, mitochondrial homeostasis, and in dictating cell survival or death. Emerging evidence from preclinical and human studies indicates an age-dependent reduction of cellular NAD⁺, possibly due to reduced synthesis and increased consumption. In preclinical models, NAD⁺ repletion extends healthspan and / or lifespan and mitigates several conditions, such as premature ageing diseases and neurodegenerative diseases. These findings suggest that NAD⁺ replenishment through NAD⁺ precursors has great potential as a therapeutic target for ageing and age-predisposed diseases, such as Alzheimer’s disease. Here, we provide an updated review on the biological activity, safety, and possible side effects of NAD⁺ precursors in preclinical and clinical studies. Major NAD⁺ precursors focused on by this review are nicotinamide riboside (NR), nicotinamide mononucleotide (NMN), and the new discovered dihydronicotinamide riboside (NRH). In summary, NAD⁺ precursors have an exciting therapeutic potential for ageing, metabolic and neurodegenerative diseases.

NAD ⁺是人类生命和健康的基本分子，因为它参与能量代谢、细胞信号传导、线粒体稳态以及决定细胞生存或死亡。^{来自临床前和人类研究的新证据表明细胞 NAD +}的年龄依赖性减少，可能是由于合成减少和消耗增加。在临床前模型中，NAD ⁺补充可延长健康寿命和/或寿命并缓解多种疾病，例如过早衰老疾病和神经退行性疾病。这些发现表明，通过 NAD ⁺补充 NAD ⁺前体具有作为衰老和年龄易感疾病（例如阿尔茨海默病）的治疗靶标的巨大潜力。^{在这里，我们提供了关于 NAD +}前体在临床前和临床研究中的生物活性、安全性和可能的​​副作用的最新评论。本综述重点关注的主要 NAD ⁺前体是烟酰胺核苷 (NR)、烟酰胺单核苷酸 (NMN) 和新发现的二氢烟酰胺核苷 (NRH)。总之，NAD ⁺前体对衰老、代谢和神经退行性疾病具有令人兴奋的治疗潜力。