Vitamin c
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The Multifaceted Role of Vitamin C: Immune Function, Cardiovascular Health, and Beyond
Vitamin C and Immune Function
Immune Defense and Antioxidant Properties
Vitamin C, also known as ascorbic acid, is a crucial micronutrient with significant antioxidant properties. It plays a vital role in supporting the immune system by enhancing various cellular functions of both the innate and adaptive immune systems. Vitamin C supports the epithelial barrier function against pathogens and promotes the oxidant scavenging activity of the skin, potentially protecting against environmental oxidative stress1. It accumulates in phagocytic cells like neutrophils, enhancing chemotaxis, phagocytosis, and microbial killing, while also aiding in the clearance of spent neutrophils to reduce tissue damage1.
Impact on Lymphocytes and Infection Susceptibility
While the role of vitamin C in lymphocytes is less clear, it has been shown to enhance the differentiation and proliferation of B- and T-cells, likely due to its gene-regulating effects. Deficiency in vitamin C impairs immunity and increases susceptibility to infections. Conversely, infections can deplete vitamin C levels due to increased inflammation and metabolic demands. Supplementation with vitamin C can help prevent and treat respiratory and systemic infections, with prophylactic doses of 100-200 mg/day being effective, while treatment of established infections may require higher doses1.
Vitamin C and Cardiovascular Health
Cholesterol and Endothelial Function
Vitamin C intake has been associated with improved cardiovascular health, particularly in individuals with diabetes or metabolic syndrome. It helps lower total cholesterol levels and reduces markers of inflammation and oxidative stress, such as C-reactive protein and interleukin-6, thereby improving endothelial function and blood flow2. Effective doses in studies ranged from 1,000 mg daily for periods of 4 weeks to 12 months2.
Primary Prevention of Cardiovascular Disease
Despite observational studies suggesting an inverse relationship between vitamin C intake and cardiovascular events, clinical trials have shown inconsistent results. A comprehensive review of randomized controlled trials found no significant difference in major cardiovascular events between vitamin C and placebo groups. The evidence was considered low to very low quality due to indirectness and imprecision, indicating that more robust trials are needed to confirm these findings3.
Vitamin C in Exercise and Muscle Function
Oxidative Stress and Inflammation
Vitamin C supplementation can attenuate oxidative stress and inflammatory responses following acute exercise. Meta-analyses of randomized clinical trials have shown that vitamin C reduces lipid peroxidation and interleukin-6 levels post-exercise, although it does not significantly affect muscle soreness or strength7. However, high doses of vitamin C may hamper training-induced adaptations in endurance performance by reducing the expression of key transcription factors involved in mitochondrial biogenesis5.
Vitamin C in Critical Illness
Sepsis and Systemic Inflammation
Vitamin C has shown potential benefits in critical illness, including sepsis, trauma, and systemic inflammation. It can modulate immune responses and enhance antioxidant reserves, potentially improving outcomes in critically ill patients. However, the evidence is not yet strong enough to establish causality, and current guidelines do not support high-dose vitamin C administration in these patients. More extensive trials are needed to validate these findings6.
Conclusion
Vitamin C is a versatile nutrient with significant roles in immune function, cardiovascular health, and exercise recovery. While it shows promise in various health contexts, more high-quality research is needed to fully understand its benefits and optimal dosing strategies. For now, maintaining adequate vitamin C intake through diet or supplementation remains a prudent approach to support overall health.
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Most relevant research papers on this topic
Vitamin C and Immune Function
Vitamin C contributes to immune defense by supporting various cellular functions of both the innate and adaptive immune systems, enhancing microbial killing, and preventing and treating respiratory and systemic infections.
Very Rigorous Journal
Highly CitedVitamin C intake potentially lowers total cholesterol to improve endothelial function in diabetic patients at increased risk of cardiovascular disease: A systematic review of randomized controlled trials
Vitamin C intake may lower total cholesterol levels and improve endothelial function in diabetic patients at increased risk of cardiovascular disease.
Systematic ReviewVitamin C supplementation for the primary prevention of cardiovascular disease.
Vitamin C supplementation as a single supplement does not show significant effectiveness in primary prevention of cardiovascular disease.
Meta-AnalysisVery Rigorous JournalVitamin C
Vitamin C is synthesized from d-glucuronate in vertebrates, with its degradation involving 2,3-diketo-l-arginine, CO2, and l-erythrulose.
Highly CitedOral administration of vitamin C decreases muscle mitochondrial biogenesis and hampers training-induced adaptations in endurance performance.
Vitamin C supplementation decreases training efficiency by hindering some cellular adaptations to exercise, potentially affecting endurance capacity in humans and rats.
RCTVery Rigorous JournalHighly CitedVitamin C for the critically ill: Is the evidence strong enough?
Vitamin C supplementation may improve clinical outcomes in critically ill patients, but larger, more randomized controlled trials are needed to confirm its effectiveness.
Systematic ReviewEffects of vitamin C on oxidative stress, inflammation, muscle soreness, and strength following acute exercise: meta-analyses of randomized clinical trials
Vitamin C supplementation reduces oxidative stress and inflammation after a single bout of exercise, without affecting muscle soreness or strength.
Meta-Analysis
Rigorous JournalVitamin C—Sources, Physiological Role, Kinetics, Deficiency, Use, Toxicity, and Determination
Vitamin C plays a diverse role in various processes, but high doses can cause side effects, such as oxalate renal stones, and its safety is relatively unknown in the general population.
Very Rigorous JournalHighly CitedVitamin C in Plants: From Functions to Biofortification
Increasing vitamin C content in crops can improve human health and enhance their nutritional value and stress resistance.
Highly CitedVitamin C in Stem Cell Reprogramming and Cancer.
Vitamin C may play a novel role as an epigenetic anticancer agent by modulating stem cell function and enhancing fibroblast reprogramming to induced pluripotent stem cells.
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