Vitamin C 101

Vitamin C

Vitamin C is a water-soluble vitamin and has been linked to many impressive health benefits. Apart from its well-known immunity boosting properties, Vitamin C is also a powerful antioxidant and a cofactor for a family of enzymes. Adequate vitamin C intake has been associated with lowered blood pressure, reduced gout attacks,  increased iron absorption and reduced heart disease and dementia risk.

Our body is unable to make Vitamin C and the vitamin C that we need must come from the foods and/or supplements that we eat daily.

How does Vitamin C improve our immunity?

Vitamin C contributes to immune defense by supporting various cellular functions of the immune system. It supports epithelial barrier function against pathogens such as virus and bacteria and promotes the antioxidant capability of the skin.

Higher levels of Vitamin C has also been shown to increase the number and function of white blood cells, resulting in increased immunity and reduced susceptibility to infections. Vitamin C deficiency thus results in impaired immunity and higher susceptibility to infections.

When we have an infection, our demand for vitamin C increases, due to enhanced inflammation and metabolic requirements to fight off the infection.

How much vitamin C do we need?

The recommended dietary allowance for healthy adults are 90mg/day for men and 75mg/day for women, with smokers requiring about 35mg more day than non-smokers. Recommended dietary allowances are merely guidelines for the MINIMUM amount needed to prevent known diseases. The actual amount of any nutrient that an individual will need to thrive varies widely, and depends on factors such as our lifestyle, genetics, quality of food and gut health.

Studies have shown that prevention of infection requires plasma levels of 100-200mg/day. Treatment of established infections requires significantly higher gram doses of the vitamin to compensate for the increased inflammatory response and metabolic demand.

Oral Vitamin C vs IV Vitamin C

The difference between oral and vitamin supplements is bioavailability – the amount of an ingredient that gets absorbed for use in the body. Read More on Bioavailability here

Approximately 70%-90% of vitamin C is absorbed orally at moderate intakes of 30-180 mg/day. At doses above 1g/day, absorption falls to less than 50%, with the rest excreted in the urine. Results from studies looking at the absorption and use of vitamin C showed that even with very high doses of oral vitamin C (3grams) taken every 4 hourly, the peak plasma concentrations was only 3.87mg/dL.

Achieving the levels required for treatment for existing infections is not achievable through oral supplementation alone. Daily oral supplementation is useful to maintain vitamin C levels when an individual is healthy and not facing any additional stress to their bodies, such as infections, heart disease, insomnia, work stress and/or any other chronic medical conditions. When there is increased inflammation and demand from the body, supplemental IV therapy may be needed to achieve the effective amount that is needed.

Vitamin C
  1. Institute of Medicine. Food and Nutrition Board. Dietary Reference Intakes for Vitamin C, Vitamin E, Selenium, and Carotenoids. Washington, DC: National Academy Press, 2000.
  2. Vitamin C and Immune Function. Nutrients. 2017 Nov 3;9(11). pii: E1211. doi: 10.3390/nu9111211.
  3. Jacob RA, Sotoudeh G. Vitamin C function and status in chronic disease. Nutr Clin Care 2002;5:66-74. [PubMed abstract]
  4. Padayatty SJ, Sun H, Wang Y, Riordan HD, Hewitt SM, Katz A, Wesley RA, Levine M. Vitamin C pharmacokinetics: implications for oral and intravenous use. Ann Intern Med 2004;140:533-7. [PubMed abstract]
  5. 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.
Dr Deborah Wong

Dr Deborah Wong

Deborah is senior medical advisor at Life Clinic. Dr Deborah Wong obtained her MBBS from the National University of Singapore and post graduate training in Family Medicine with the College of Family Physicians Singapore. She is currently pursuing her Fellowship with the Australasian College of Nutritional and Environment Medicine.

She has a special interest in preventive health, women’s health and sports medicine. She has also undergone training and attained various certifications in exercise medicine and Clinical Orthopedic Manual Therapy. She believes that healthcare should be holistic, and treatment should involve mind, body and soul. With a passion for movement, she is also co-owner at Breathe Pilates and enjoys olympic weightlifting in her spare time.

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