Everything You Need To Know About Vitamin C

Written by Esther Diong on 22 April 2021
Medically Reviewed by Dr. K. Updated as of 9 October 2021.

Everything You Need To Know About Vitamin C

Vitamin C and the Common Cold

The common cold is one of the most common infectious diseases in humans, and it is not something one would want to catch, especially during this Covid-19 pandemic. Vitamin C has often been claimed by many to be an effective treatment for the common cold.

What is Vitamin C?

Vitamin C, also known as L-ascorbic acid, is a water-soluble vitamin that is naturally present in many foods, added to others, and available as a dietary supplement. Vitamin C is an essential micronutrient because the human body is unable to synthesize vitamin C endogenously, on your own in your body.

Vitamin C is a potent antioxidant. The role of an antioxidant is to neutralize unstable compounds in the body, known as free radicals, and help to prevent or reverse cellular damages caused by free radicals. Vitamin C is involved in numerous biochemical processes in the body, including the immune system.

For adults, the recommended daily amount for vitamin C is 65 to 90 milligrams (mg) a day, and the upper limit is 2,000 mg a day. Breastfeeding women require an extra 30mg and people who smoke require an extra 35mg per day. 

Although too much dietary vitamin C is unlikely to be harmful, megadoses of vitamin C supplements might cause:

  • Diarrhea;
  • Nausea;
  • Vomiting;
  • Heartburn;
  • Abdominal cramps;
  • Headache;
  • Insomnia.

For most people, a healthy diet with a variety of fruits and vegetables would provide an adequate amount of vitamin C. For example, an orange or a cup of strawberries, chopped red pepper or broccoli, provides enough vitamin C for the day.

How does it affect immunity?

Vitamin C affects your immune system via several pathways. As vitamin C is an antioxidant, it helps to reduce inflammation in the body, which may help to improve an individual’s immunity due to the reduced burden in the body. The vitamin promotes wound healing and also boosts collagen production in humans, which helps to keep skin healthy as the skin is the first line of defense on preventing harmful compounds from entering the body.

Vitamin C enhances phagocytes’ activities, these are the immune cells which “swallow” and break down harmful bacteria and other particles. In addition to that, the vitamin also promotes the growth and spread of lymphocytes, an immune cell that increases the body’s circulating antibodies to fight off foreign or harmful substances in the body.

In studies of its effectiveness against viruses that cause the common cold, vitamin C does not seem to reduce the chance of getting the cold, however, it may help one to recover faster and reduce the severity of the symptoms.

Vitamin C is highly concentrated in immune cells and is rapidly depleted during an infection. In addition to that, vitamin C deficiency significantly weakens the immune system and increases the risk of infections. Hence, for this reason, having adequate vitamin C during an infection is vital.

Do you need supplements?

Vitamin C is a water-soluble vitamin, which means the excess amounts are not stored in the body, but instead eliminated from the body. Excess amounts of vitamin C do not indicate that the body would be absorbing more vitamin C.

Vitamin C may help shorten the duration and severity of the common colds. However, high doses of vitamin C supplements may cause diarrhea. The best method would be to consume a diet that has a variety of fruits and vegetables, which naturally provide ample amounts of vitamin C a healthy person needs along with many other nutrients and antioxidants.

If you have any concerns about vitamin C supplements, please do consult your healthcare provider before consuming them on a daily basis.


Referenced on 21.4.2021:

  1. https://www.mayoclinic.org/diseases-conditions/common-cold/symptoms-causes/syc-20351605 
  2. Carr AC, Maggini S. Vitamin C and Immune Function. Nutrients. 2017 Nov 3;9(11):1211. doi: 10.3390/nu9111211. PMID: 29099763; PMCID: PMC5707683. 
  3. https://ods.od.nih.gov/factsheets/VitaminC-HealthProfessional/ 
  4. https://www.mayoclinic.org/healthy-lifestyle/nutrition-and-healthy-eating/expert-answers/vitamin-c/faq-20058030#:~:text=For%20adults%2C%20the%20recommended%20daily,Diarrhea 
  5. Hemilä H, Chalker E. Vitamin C for preventing and treating the common cold. Cochrane Database Syst Rev. 2013 Jan 31;(1):CD000980. doi: 10.1002/14651858.CD000980.pub4. PMID: 23440782. 
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  10. Sexton DJ, et al. The common cold in adults: Treatment and prevention. https://www.uptodate.com/contents/search. Accessed Feb. 5, 2016.
  11. Ask Mayo Expert. Upper respiratory tract infection. Rochester, Minn.: Mayo Foundation for Medical Education and Research; 2017.
  12. Is it a cold or the flu? U.S. Food and Drug Administration. https://www.fda.gov/forconsumers/consumerupdates/ucm092805.htm. Accessed March 15, 2019.
  13. Vitamin C. Natural Medicines Comprehensive Database. https://www.naturaldatabase.com. Accessed March 15, 2019.
  14. Echinacea. Natural Medicines Comprehensive Database. https://www.naturaldatabase.com. Accessed March 15, 2019.
  15. Zinc. Natural Medicines Comprehensive Database. https://www.naturaldatabase.com. Accessed March 15, 2019.
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  17. Lowry JA, et al. Over-the-counter medications: Update on cough and cold preparations. Pediatrics in Review. 2015;36:286.

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