Uridine, a pyrimidine nucleoside, plays a crucial role in various biological processes, including macromolecule synthesis, circadian rhythms, inflammatory response, and aging. It is involved in the formation of uridine diphosphate glucose (UDPG) for glycogen synthesis and UDP-GlcNAc for O-GlcNAcylation, a post-translational modification. Uridine also affects body temperature and circadian rhythms, with elevated plasma levels leading to decreased body temperature and altered feeding behavior. In terms of metabolic diseases, uridine can have both beneficial and detrimental effects. It can improve glucose tolerance and insulin secretion but can also promote insulin resistance and fatty liver. Uridine's impact on protein modification through O-GlcNAcylation is significant, as it can worsen or protect against various diseases, including diabetes, Alzheimer's, and cancer. The regulation of uridine levels and its metabolism is critical for maintaining cellular homeostasis and preventing the onset of metabolic disorders. Further research is needed to fully understand the complex mechanisms and therapeutic potential of uridine in treating these conditions.Uridine, a pyrimidine nucleoside, plays a crucial role in various biological processes, including macromolecule synthesis, circadian rhythms, inflammatory response, and aging. It is involved in the formation of uridine diphosphate glucose (UDPG) for glycogen synthesis and UDP-GlcNAc for O-GlcNAcylation, a post-translational modification. Uridine also affects body temperature and circadian rhythms, with elevated plasma levels leading to decreased body temperature and altered feeding behavior. In terms of metabolic diseases, uridine can have both beneficial and detrimental effects. It can improve glucose tolerance and insulin secretion but can also promote insulin resistance and fatty liver. Uridine's impact on protein modification through O-GlcNAcylation is significant, as it can worsen or protect against various diseases, including diabetes, Alzheimer's, and cancer. The regulation of uridine levels and its metabolism is critical for maintaining cellular homeostasis and preventing the onset of metabolic disorders. Further research is needed to fully understand the complex mechanisms and therapeutic potential of uridine in treating these conditions.