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Abstract Study question How does nicotinamide adenine dinucleotide (NAD+) metabolism influence oocyte quality under various reproductive conditions, particularly in relation to nicotinamide mononucleotide (NMN) supplementation? Summary answer NAD+ metabolism influences oocyte quality by improving mitochondrial function, reducing oxidative stress, and maintaining meiotic progression. NMN supplementation enhances these processes in preclinical models. What is known already Oocyte quality refers to the ability of an egg to mature, fertilise, and support early embryo development. Its decline is associated with ageing, oxidative stress, and metabolic dysfunction. NAD+ metabolism plays a crucial role in cellular energy production, DNA repair, and redox balance. NMN, a key precursor of NAD+, has been shown to increase NAD+ levels. While studies suggest that NMN supplementation enhances oocyte quality, specific mechanisms and outcomes remain underexplored. Study design, size, duration A systematic review was conducted following PRISMA guidelines. An initial search across three databases (MEDLINE, EMBASE, Scopus) yielded 486 results. After screening, seven high-quality studies were included in the final synthesis. These studies, published between 2015 and 2024, met inclusion criteria of peer-reviewed original research and included NMN in experimental interventions. The NHLBI–NIH tool was used to evaluate study quality, with included papers scoring 8.5 to 10. Participants/materials, setting, methods Preclinical studies were conducted in China (six studies) and Australia (one study). Five studies used mouse models, while two papers investigated porcine and bovine oocytes. Experimental designs involved NMN supplementation via in vitro (oocyte culture) and in vivo (oral/intraperitoneal) delivery. Control groups assessed the impact on parameters under stress conditions, including ageing, high-fat diets, and environmental toxins. Single-cell transcriptomic data from forty-six human oocytes was used to analyse differentially expressed genes. Main results and the role of chance NAD+ metabolism was shown to be essential for oocyte quality by supporting mitochondrial function, reducing oxidative stress, and maintaining meiotic progression. NMN supplementation consistently improved mitochondrial function by upregulating biogenesis genes (e.g. PGC1A, NRF1), enhancing redox balance through antioxidant enzymes (e.g. SOD1, CAT), and stabilising mitochondrial dynamics (e.g. MFN2, DRP1). NMN reduced oxidative stress markers such as reactive oxygen species, supported meiotic spindle integrity, and corrected chromosomal misalignments. Key NAD+-dependent enzymes, including sirtuins, were identified as regulators of redox balance, apoptosis, and mitochondrial health. The review highlighted variability in NMN dosing, delivery methods, and timing. Functional improvements were evidenced by enhanced oocyte maturation rates and spindle morphology. Human oocyte transcriptomic data showed differential expression in genes highlighted in the systematic review. Limitations, reasons for caution The systematic review findings are based on animal studies, which may not fully reflect human oocyte biology. Additionally, variations in NMN supplementation protocols could influence outcomes. Standardisation in future research is necessary to ensure consistency and translatability to clinical settings. Wider implications of the findings These findings underscore the potential of targeting NAD+ metabolism and using NMN supplementation to improve oocyte quality, offering promising avenues for mitigating age-related fertility decline. This research provides a foundation for developing NAD+-based strategies in assisted reproductive technologies to enhance reproductive outcomes. Trial registration number No