Introduction: What Is Vitamin C?

Vitamin C, also known as ascorbic acid, is a water-soluble vitamin that the human body is unable to produce on its own, unlike other animals[1]. Hence, external supplement of vitamin C is crucial. Deficiency of this vitamin is associated with a medical condition called scurvy, which is initially characterised by fatigue, malaise, and gum inflammation[2], and can lead to easy bruising, gum diseases, and poor wound healing if the situation continues[3].

Vitamin C is also an antioxidant that can help protect your body’s cell from the oxidative stress and damage from free radicals. Free radicals are products of food breakdown or tobacco and UV exposure and has associations with many diseases such as heart diseases and cancer[4].

Read on to find out more about the different functions of vitamin C in maintaining a healthy lifestyle and know how much is enough for you.

Function #1 of Vitamin C – Dealing with the common cold

Perhaps the most well-known function of vitamin C is in the management of the common cold. Since being advocated by Nobel laureate Linus Pauling in the 1970s[5], there continues to have much interest in the use of vitamin C for the prevention and treatment of the common cold. An analysis carried out in 2007 has shown a significant decrease in illness duration with vitamin C taken before onset of symptoms[6,7].

Function #2 of Vitamin C – Antioxidant and cancer

Vitamin C has been proven to be able to limit formation of carcinogens (i.e., products that increase the risk of developing cancer) [8]. It also has antioxidant effects that can potentially help reduce the oxidative damage and subsequently the risks of cancer[9]. However, it is also noted that evidence from prospective studies have garnered inconsistent results regarding the use of vitamin C for cancer prevention. A study on more than 80,000 women from the Nurses’ Health Study found out that consumption of 200mg per day of vitamin C was associated with a lower risk of developing breast cancer as compared to 70mg per day of vitamin C intake[10]. On the flip side, another study on more than 30,000 women in Iowa did not find any significant results on vitamin C intake and the prevention of breast cancer[11].

Function #3 of Vitamin C – Eye diseases

A less well-known function of vitamin C is perhaps its role in eye diseases, particularly cataracts and age-related macular degeneration (AMD).

A study held in the Netherlands found that a high dietary intake of certain vitamins, including vitamin C, in the elderly was associated with a lower risk of developing AMD[12]. However, subsequent analysis of 12 studies has not found similar association and did not support the use of routine vitamin supplementation to prevent AMD[13]. In the Age-Related Eye Disease Study (AREDS), high dose of selected antioxidants, including 500mg of vitamin C, were related to a 28% lowered risk of AMD progression[14]. As for cataracts, a high dietary intake of vitamin C was also associated with a lower risk in some studies[8]. A Japanese study studied more than 30,000 people aged 45 to 64 for 5 years and found a similar result in terms of cataracts risk[15].

Function #4 of Vitamin C – Collagen formation

Vitamin C has also been found to be crucial in collagen synthesis and soft tissue formation, by acting as a co-factor in the formation of collagen[16]. This can potentially help in wound healing, skin health[17], and even your gum and teeth help by keeping your gums strong and subsequently being more able to hold your teeth in place[18].

Sources of Vitamin C, and how much is required

Dietary sources of vitamin C usually come from fruits and vegetables. The major sources of vitamin C can be found in citrus fruits like oranges and lemons. Vegetables like broccoli and chili peppers also contain a relatively high amount of vitamin C content[1]. As for supplements, vitamin C are usually found in the form of ascorbic acid, which is found to be biologically as active as the vitamin C found to be naturally occurring in food[19].

The recommended daily allowance (RDA) of vitamin C for a healthy adult is 90mg, although special populations like smokers may require a higher amount[20]. Although vitamin C is generally considered to be safe, there may be side effects such as kidney stones formation, especially in very high doses of vitamin C[20]. Hence, it is recommended to not exceed a total daily dose of 2g of vitamin C, including both dietary and supplementary sources[1].

Conclusion

Vitamin C is a water-soluble vitamin that the human body is unable to produce on its own, and hence external supplementation is critical. It has important functions in not just immunity, but also as an antioxidant with certain evidence in management of eye diseases as well. Although generally considered safe, it is recommended to keep within a daily dose of 2g of vitamin C to prevent possible side effects like kidney stones and enhanced iron absorption.

References

1. National Institutes of Health (NIH), Office of Dietary Supplements. Vitamin C: Fact Sheet for Health Professionals. 2021 March. Available on: https://ods.od.nih.gov/factsheets/VitaminC-HealthProfessional/
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3. Léger D. Scurvy: re-emergence of nutritional deficiencies. Can Fam Physician. 2008;54(10):1403-1406.
4. Mayo Clinic. Vitamin C. 2020 November. Available on: https://www.mayoclinic.org/drugs-supplements-vitamin-c/art-20363932
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7. Ran L, Zhao W, Wang J, et al. Extra Dose of Vitamin C Based on a Daily Supplementation Shortens the Common Cold: A Meta-Analysis of 9 Randomized Controlled Trials. Biomed Res Int. 2018 Jul 5;2018:1837634.
8. Carr AC, Frei B. Toward a new recommended dietary allowance for vitamin C based on antioxidant and health effects in humans. Am J Clin Nutr. 1999;69:1086-107.
9. Li Y, Schellhorn HE. New developments and novel therapeutic perspectives for vitamin C. J Nutr. 2007;137:2171-84.
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11. Kushi LH, Fee RM, Sellers TA, et al. Intake of vitamins A, C, and E and postmenopausal breast cancer. The Iowa Women’s Health Study. Am J Epidemiol. 1996;144:165-74.
12. van Leeuwen R, Boekhoorn S, Vingerling JR, et al. Dietary intake of antioxidants and risk of age-related macular degeneration. JAMA. 2005;294:3101-7.
13. Chong EW, Wong TY, Kreis AJ, et al. Dietary antioxidants and primary prevention of age-related macular degeneration: systematic review and meta-analysis. BMJ. 2007;335:755.
14. Age-Related Eye Disease Study Research Group. A randomized, placebo-controlled, clinical trial of high-dose supplementation with vitamins C and E, beta carotene, and zinc for age-related macular degeneration and vision loss: AREDS report no. 8. Arch Ophthalmol. 2001;119:1417-36.
15. Yoshida M, Takashima Y, Inoue M, et al.; JPHC Study Group. Prospective study showing that dietary vitamin C reduced the risk of age-related cataracts in a middle-aged Japanese population. Eur J Nutr. 2007;46:118-24.
16. DePhillipo NN, Aman ZS, Kennedy MI, et al. Efficacy of Vitamin C Supplementation on Collagen Synthesis and Oxidative Stress After Musculoskeletal Injuries: A Systematic Review. Orthop J Sports Med. 2018;6(10)
17. Pullar JM, Carr AC, Vissers MCM. The Roles of Vitamin C in Skin Health. Nutrients. 2017;9(8):866.
18. 10 Vitamins and Supplements for Gum Health and Gum Disease. 2021 Apr. Available on: https://www.healthline.com/nutrition/vitamins-for-gums
19. Bates CJ. Bioavailability of vitamin C. Eur J Clin Nutr. 1997;51 (Suppl 1):S28-33.
20. Institute of Medicine. Food and Nutrition Board. Dietary Reference Intakes for Vitamin C, Vitamin E, Selenium, and Carotenoids external link disclaimer. Washington, DC: National Academy Press, 2000.