Vitamin c biosynthesis in humans
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Human Vitamin C Biosynthesis: Genetic Loss and Dietary Dependence
Humans are unable to synthesize vitamin C due to the loss of the L-gulono-γ-lactone oxidase (GULO) gene, which is essential for the final step in the endogenous production of ascorbic acid. This genetic mutation is shared with other primates and some animal species, making humans entirely dependent on dietary sources of vitamin C to meet physiological needs Sekar2024Grădinaru2025Padayatty2016. The absence of this biosynthetic pathway is considered an inborn metabolic error, and its evolutionary cause is still debated, with hypotheses including dietary sufficiency, neutral selection, and improved redox homeostasis due to the avoidance of potentially toxic byproducts like hydrogen peroxide Hornung2019Grădinaru2025.
Evolutionary Implications of GULO Gene Loss in Humans
The evolutionary loss of the GULO gene in humans and some other species has been linked to adaptations that may have provided survival advantages. One hypothesis suggests that the presence of the glucose transporter Glut-1 in human red blood cells allows for efficient recycling and uptake of vitamin C, reducing the daily requirement and offering protection during periods of dietary scarcity . This adaptation may have helped individuals survive seasonal fluctuations in food availability, despite their inability to synthesize vitamin C .
Physiological Roles and Health Implications of Vitamin C
Vitamin C is crucial for many biological processes, including collagen synthesis, immune function, antioxidant defense, and as a cofactor for several enzymes involved in metabolism and gene regulation Tucaliuc2022Grădinaru2025Padayatty2016. Its deficiency can lead to scurvy and may increase susceptibility to diseases such as cancer, cardiovascular disorders, and cognitive decline Sekar2024Tucaliuc2022Grădinaru2025. In cancer, vitamin C deficiency has been associated with tumor growth, metastasis, and resistance to therapy, highlighting the importance of maintaining adequate vitamin C levels in humans who cannot produce it endogenously .
Industrial and Microbial Biosynthesis of Vitamin C
Since humans cannot synthesize vitamin C, industrial production methods have been developed to meet global demand. The main approaches include chemical synthesis and microbial fermentation, with the latter being favored for its environmental friendliness and cost-effectiveness Chen2021Zhang2024Tucaliuc2022. Microbial biosynthesis typically utilizes the L-sorbose and D-gluconate pathways, with ongoing research focused on optimizing dehydrogenase enzymes involved in these processes to improve yield and efficiency Chen2021Zhang2024Tucaliuc2022.
Conclusion
Humans' inability to biosynthesize vitamin C is due to the evolutionary loss of the GULO gene, making dietary intake essential for health. This genetic change has shaped human physiology and disease susceptibility, while also driving the development of industrial vitamin C production methods. Understanding the genetic, physiological, and industrial aspects of vitamin C biosynthesis is crucial for addressing health needs and ensuring adequate supply for populations worldwide.
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