Introduction to Vitamin C
Vitamin C, also known as ascorbic acid, is a water-soluble vitamin that plays a crucial role in maintaining optimal health. As an essential nutrient, vitamin C cannot be synthesized by the human body and must be obtained through dietary sources or supplements (Chambial et al., 2013). This vitamin is involved in numerous physiological processes, including collagen synthesis, wound healing, immune function, and acting as a potent antioxidant to protect cells from oxidative damage (Carr & Frei, 1999). Citrus fruits, tomatoes, potatoes, capsicums, kiwifruit, broccoli, and strawberries are among the best dietary sources of vitamin C (Carr & Frei, 1999).
Recommended Intakes and Deficiency
The recommended dietary allowance (RDA) for vitamin C, as established by the Institute of Medicine (2000), is 75-90 mg per day for adults. However, smokers require an additional 35 mg per day to compensate for the increased oxidative stress caused by cigarette smoke. Vitamin C deficiency, although rare in developed countries, can lead to scurvy, a condition characterised by symptoms such as fatigue, inflammation of the gums, impaired wound healing, and joint pain (Carr & Frei, 1999). Populations at higher risk of vitamin C deficiency include smokers, individuals with limited food variety, and those with certain chronic diseases or disorders that impact nutrient absorption (Carr & Frei, 1999).
Potential Health Benefits
Cancer Prevention and Treatment
Epidemiological studies have suggested that higher vitamin C intakes are associated with a lower risk of several types of cancer, possibly due to the vitamin’s antioxidant properties (Carr & Frei, 1999). However, randomized controlled trials have not found a significant preventive effect of vitamin C supplementation on cancer risk (Carr & Frei, 1999). Recent interest has focused on the potential use of high-dose intravenous vitamin C as a complementary therapy in cancer treatment, but more research is needed to establish its efficacy and safety (Padayatty et al., 2006).
Cardiovascular Disease Prevention
Observational studies have indicated that higher vitamin C intakes are associated with a reduced risk of cardiovascular disease (Moser & Chun, 2016). However, randomized controlled trials have not consistently demonstrated a clear benefit of vitamin C supplementation in the prevention or treatment of cardiovascular disease (Moser & Chun, 2016). The potential protective role of vitamin C in cardiovascular health may be attributed to its antioxidant properties and its involvement in endothelial function and lipid metabolism (Moser & Chun, 2016).
Eye Health: Age-Related Macular Degeneration and Cataracts
Vitamin C has been investigated for its potential role in slowing the progression of age-related macular degeneration (AMD) and cataracts, two common eye disorders in older adults. While some studies suggest that vitamin C may help slow the progression of these conditions, the evidence for prevention has been mixed (Carr & Frei, 1999). More research is needed to clarify the role of vitamin C in maintaining eye health and preventing age-related eye diseases.
Common Cold Prevention and Treatment
Vitamin C has long been associated with the prevention and treatment of the common cold. However, a Cochrane systematic review concluded that vitamin C supplementation does not appear to prevent colds in the general population (Hemilä & Chalker, 2013). The review did find that vitamin C supplementation may slightly reduce the duration and severity of cold symptoms, particularly in individuals under heavy physical stress, such as marathon runners and skiers (Hemilä & Chalker, 2013).
Safety and Side Effects
Vitamin C is generally considered safe, even at high intakes. However, consuming large doses of vitamin C supplements (above 1000 mg/day) can cause side effects such as diarrhoea, nausea, and abdominal cramps (Carr & Frei, 1999). In some individuals, high vitamin C intakes may also increase the risk of developing kidney stones (Carr & Frei, 1999). The tolerable upper intake level (UL) for adults, as set by the Institute of Medicine (2000), is 2000 mg per day.
Conclusion
Vitamin C is an essential nutrient that plays a vital role in maintaining optimal health. Its antioxidant properties and involvement in various physiological processes, such as collagen synthesis and immune function, highlight its importance in the human body. While fruits and vegetables remain the best sources of vitamin C, supplements can be useful for individuals with higher requirements or limited access to vitamin C-rich foods.
Although research has suggested potential roles for vitamin C in the prevention and treatment of various chronic diseases, such as cancer, cardiovascular disease, and age-related eye disorders, more evidence is needed to confirm the benefits of supplementation. Consuming a varied diet rich in vitamin C is a safe and effective way to ensure adequate intake of this essential nutrient and support overall health and well-being.
Key Highlights and Actionable Tips
- Vitamin C is an essential nutrient that cannot be synthesized by the human body and must be obtained through dietary sources or supplements.
- The recommended dietary allowance (RDA) for vitamin C is 75-90 mg per day for adults, with smokers requiring an additional 35 mg per day.
- Citrus fruits, tomatoes, potatoes, capsicums, kiwifruit, broccoli, and strawberries are among the best dietary sources of vitamin C.
- Vitamin C plays a crucial role in collagen synthesis, wound healing, immune function, and acting as a potent antioxidant to protect cells from oxidative damage.
- While some studies suggest potential roles for vitamin C in the prevention and treatment of various chronic diseases, more research is needed to confirm the benefits of supplementation.
- Consuming a varied diet rich in vitamin C is a safe and effective way to ensure adequate intake and support overall health and well-being.
What is the tolerable upper intake level (UL) for vitamin C in adults?
The tolerable upper intake level (UL) for vitamin C in adults, as set by the Institute of Medicine (2000), is 2000 mg per day. Consuming vitamin C supplements above this level may cause side effects such as diarrhoea, nausea, and abdominal cramps.
Can vitamin C supplementation help prevent or treat the common cold?
While vitamin C has long been associated with the prevention and treatment of the common cold, a Cochrane systematic review concluded that vitamin C supplementation does not appear to prevent colds in the general population. However, the review did find that vitamin C supplementation may slightly reduce the duration and severity of cold symptoms, particularly in individuals under heavy physical stress, such as marathon runners and skiers.
Are there any populations at higher risk of vitamin C deficiency?
Yes, certain populations are at a higher risk of vitamin C deficiency. These include smokers, individuals with limited food variety, and those with certain chronic diseases or disorders that impact nutrient absorption. Smokers require an additional 35 mg of vitamin C per day to compensate for the increased oxidative stress caused by cigarette smoke.
What is the potential role of vitamin C in cancer prevention and treatment?
Epidemiological studies have suggested that higher vitamin C intakes are associated with a lower risk of several types of cancer, possibly due to the vitamin’s antioxidant properties. However, randomized controlled trials have not found a significant preventive effect of vitamin C supplementation on cancer risk. Recent interest has focused on the potential use of high-dose intravenous vitamin C as a complementary therapy in cancer treatment, but more research is needed to establish its efficacy and safety.
Can vitamin C supplementation help prevent or treat cardiovascular disease?
Observational studies have indicated that higher vitamin C intakes are associated with a reduced risk of cardiovascular disease. However, randomized controlled trials have not consistently demonstrated a clear benefit of vitamin C supplementation in the prevention or treatment of cardiovascular disease. The potential protective role of vitamin C in cardiovascular health may be attributed to its antioxidant properties and its involvement in endothelial function and lipid metabolism.
References
Carr, A. C., & Frei, B. (1999). Toward a new recommended dietary allowance for vitamin C based on antioxidant and health effects in humans. The American Journal of Clinical Nutrition, 69(6), 1086-1107. https://doi.org/10.1093/ajcn/69.6.1086
Chambial, S., Dwivedi, S., Shukla, K. K., John, P. J., & Sharma, P. (2013). Vitamin C in disease prevention and cure: an overview. Indian Journal of Clinical Biochemistry, 28(4), 314-328. https://doi.org/10.1007/s12291-013-0375-3
Hemilä, H., & Chalker, E. (2013). Vitamin C for preventing and treating the common cold. Cochrane Database of Systematic Reviews, (1). https://doi.org/10.1002/14651858.CD000980.pub4
Institute of Medicine (2000). Dietary Reference Intakes for Vitamin C, Vitamin E, Selenium, and Carotenoids. Washington, DC: The National Academies Press. https://doi.org/10.17226/9810
Moser, M. A., & Chun, O. K. (2016). Vitamin C and heart health: a review based on findings from epidemiologic studies. International Journal of Molecular Sciences, 17(8), 1328. https://doi.org/10.3390/ijms17081328
Padayatty, S. J., Riordan, H. D., Hewitt, S. M., Katz, A., Hoffer, L. J., & Levine, M. (2006). Intravenously administered vitamin C as cancer therapy: three cases. CMAJ, 174(7), 937-942. https://doi.org/10.1503/cmaj.050346
