Vitamin c and antioxidants
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The Dual Role of Vitamin C: Antioxidant and Pro-Oxidant Properties
Introduction to Vitamin C and Antioxidants
Vitamin C, also known as ascorbic acid, is a well-known antioxidant that plays a crucial role in neutralizing free radicals and protecting cells from oxidative damage. It is commonly found in fruits and vegetables and is often used as a dietary supplement to boost overall health1 7. However, recent research has highlighted that vitamin C can also exhibit pro-oxidant properties under certain conditions, adding complexity to its role in human health1 4 5.
Antioxidant Mechanisms of Vitamin C
Free Radical Scavenging
Vitamin C is a potent water-soluble antioxidant that donates electrons to neutralize reactive oxygen species (ROS), thereby preventing oxidative damage to lipids, proteins, and DNA3 7 9. This antioxidative action is crucial in protecting cells from oxidative stress, which is linked to various chronic diseases such as atherosclerosis and cancer9.
Enzyme Cofactor Functions
Vitamin C serves as an essential cofactor for several enzymes, including those involved in collagen synthesis and the regulation of hypoxia-inducible factor (HIF)-1, which plays a role in tumor growth and energy metabolism3. By supporting these enzymatic functions, vitamin C contributes to maintaining cellular health and preventing oxidative damage3.
Pro-Oxidant Activity of Vitamin C
Conditions for Pro-Oxidant Effects
While vitamin C is primarily known for its antioxidant properties, it can act as a pro-oxidant under certain conditions, particularly in the presence of transition metals like iron and copper4 7 8. This pro-oxidant activity can lead to the generation of free radicals, which may cause cellular damage4 8.
Impact on Inflammatory Conditions
Research has shown that vitamin C supplementation can increase oxidative stress in humans during inflammatory conditions. For instance, in a study involving acute muscle injury induced by eccentric exercise, subjects who received vitamin C and N-acetyl-cysteine (NAC) exhibited higher levels of oxidative stress markers compared to those who received a placebo2. This suggests that vitamin C can exacerbate oxidative damage under specific inflammatory conditions2.
Vitamin C in Disease Prevention and Health
Cardiovascular and Cancer Prevention
Epidemiological studies have associated high intake of fruits and vegetables, which are rich in vitamin C, with a lower risk of cardiovascular diseases, stroke, and cancer9. However, intervention studies with vitamin C alone have shown mixed results, indicating that the protective effects may not be solely attributable to vitamin C but rather to a combination of nutrients found in whole foods9.
Athletic Performance and Recovery
Vitamin C, in combination with other antioxidants like glutathione, has been shown to improve metabolic function, skeletal muscle oxygenation, and cardiac function during prolonged exercise in athletes6. This suggests that vitamin C can enhance athletic performance and recovery, although its pro-oxidant effects should be carefully considered6.
Conclusion
Vitamin C exhibits a dual role as both an antioxidant and a pro-oxidant, depending on the context and conditions. While it provides significant protective benefits against oxidative stress and supports various physiological functions, its pro-oxidant activity under certain conditions warrants caution. Further research is needed to fully understand the implications of these dual roles and to optimize the use of vitamin C in health and disease prevention.
Sources and full results
Most relevant research papers on this topic
Two Faces of Vitamin C—Antioxidative and Pro-Oxidative Agent
Vitamin C has both antioxidant and pro-oxidative effects, with potential benefits in cancer prevention, central nervous system maintenance, and oxidative DNA damage prevention.
Very Rigorous Journal
Highly CitedSupplementation with vitamin C and N-acetyl-cysteine increases oxidative stress in humans after an acute muscle injury induced by eccentric exercise.
Vitamin C and N-acetyl-cysteine supplementation after an acute muscle injury can transiently increase tissue damage and oxidative stress.
RCTHighly CitedVitamins C and E: beneficial effects from a mechanistic perspective.
Vitamin C and E supplementation may help control tumor progression, infections, and inflammation by regulating tumor growth, energy metabolism, and neutrophil function.
Highly CitedThe pro-oxidant chemistry of the natural antioxidants vitamin C, vitamin E, carotenoids and flavonoids.
Natural antioxidants like vitamin C, vitamin E, carotenoids, and flavonoids can be beneficial for health, but at higher doses or under certain conditions, they may exhibit toxic pro-oxidant activities.
Highly CitedVitamin C exhibits pro-oxidant properties
Vitamin C, marketed as an antioxidant, can also exhibit pro-oxidant properties in healthy humans when administered as a dietary supplement.
Highly CitedEnhancing Supplemental Effects of Acute Natural Antioxidant Derived from Yeast Fermentation and Vitamin C on Sports Performance in Triathlon Athletes: A Randomized, Double-Blinded, Placebo-Controlled, Crossover Trial
Combined vitamin C and glutathione supplementation improves metabolic function, skeletal oxygenation, cardiac function, and antioxidant function during prolonged submaximal exercise in middle-aged triathletes.
RCTAntioxidant and pro-oxidant activity of Vitamin C in oral environment.
Vitamin C acts as an antioxidant in physiologic conditions and a pro-oxidant in pathological conditions, with further studies needed to confirm its pro-oxidant activity.
Systematic ReviewHighly CitedVitamin C as an Antioxidant: Evaluation of Its Role in Disease Prevention
Vitamin C's role in disease prevention remains unclear, but diets high in fruits and vegetables may lower the risk of cardiovascular disease, stroke, and cancer.
Highly CitedSupplementation with cactus pear (Opuntia ficus-indica) fruit decreases oxidative stress in healthy humans: a comparative study with vitamin C.
Cactus pear fruit supplementation improves antioxidant status and decreases oxidative damage to lipids in healthy humans, while vitamin C supplementation does not significantly affect body oxidative stress.
RCTHighly Cited