What is vitamin C?
Vitamin C, also known as ascorbic acid, is a water-soluble vitamin that is naturally occurring in some foods. It is considered an essential vitamin because humans are not able to synthesize it within their bodies. Vitamin C is necessary for the biosynthesis of collagen, L-carnitine, and certain neurotransmitters and is involved in protein metabolism. In addition to all of these functions, vitamin C is a physiological antioxidant, meaning that it can help limit the damaging effects of free radicals which can help prevent or delay the development of certain cancers, cardiovascular disease, and other diseases that oxidative stress plays a causal role in. Vitamin C also contributes to immune function and improves the absorption of nonheme iron (the iron present in plant-based foods)1.
How much do I need?
For males age 19 and up, Health Canada recommends 90 mg/day of vitamin C.
For females age 19 and up, Health Canada recommends 75 mg/day of vitamin C2.
Vitamin C consumed through food or supplements produce concentrations within the body that are tightly controlled. At moderate intakes of 30-180 mg/day, approximately 70-90% of vitamin C is absorbed. In contrast, at doses above 1 g/day (equivalent to 1000 mg/day), absorption falls to less than 50% and any vitamin C that is absorbed and unmetabolized is excreted in the urine1. This means that taking supplements that exceed 1000 mg/day have limited (if any) benefits.
Health Canada also sets the tolerable upper limit (UL) of vitamin C at 2000 mg for both males and females age 19 and up, meaning that 2000 mg is the highest usual daily nutrient intake level likely to pose no risk of adverse health effects for almost all individuals in a life-stage and sex group. While this can sound a bit scary, the potential for adverse health effects due to extreme vitamin C intake only applies to individuals who chronically consume more than the recommended levels. If you have a single day where you consume close to 2000 mg, you have very little risk2.
Does additional vitamin C supplementation improve immune function?
According to the Practice-Based Evidence in Nutrition database, regular vitamin C supplementation may reduce cold severity and duration, and pneumonia incidence. However, for the general population it does not reduce cold incidence. Treatment with vitamin C after the onset of symptoms does not reduce cold severity or duration3.
That being said, although vitamin C may not reduce your chances of catching a cold, or any other illness, it is still an essential micronutrient that we should all be conscious of when choosing what foods to eat.
Here are a list of foods high in vitamin C:
- red bell pepper – 95 mg per ½ cup
- sweet potato – 22 mg per 1 medium cooked
- broccoli – 51 mg per ½ cup cooked
- brussels sprouts – 48 mg per ½ cup
- kale – 28 mg per ½ cup cooked
- tomatoes – 11-12 mg per ½ cup canned and 17 mg per medium raw
- oranges – 59-83 mg per medium orange
- kiwi – 64 mg per medium fruit
- strawberries – 52 mg per ½ cup
- pineapple – 42-49 mg per ½ cup4
- National Institutes of Health – Dietary Supplements. (2020, February 27). Vitamin C. Retrieved from https://ods-od-nih-gov.subzero.lib.uoguelph.ca/factsheets/VitaminC-HealthProfessional/
- Health Canada. (2010, November 19). Dietary Reference Intakes. Retrieved from https://www.canada.ca/en/health-canada/services/food-nutrition/healthy-eating/dietary-reference-intakes/tables/reference-values-vitamins-dietary-reference-intakes-tables-2005.html
- Smith, M. A. (2019). Does vitamin C supplementation improve immune function, including preventing or treating the common cold? Practice-based Evidence in Nutrition. Retrieved March 15, 2020, from https://www-pennutrition-com.subzero.lib.uoguelph.ca/KnowledgePathway.aspx?kpid=16006&pqcatid=146&pqid=2355&kppid=2356&book=Evidence&num=1#Evidence
- Dietitians of Canada. (2016). Food Sources of Vitamin C. [Handout]. Practice-based Evidence in Nutrition. https://www-pennutrition-com.subzero.lib.uoguelph.ca/viewhandout.aspx?Portal=UbY=&id=JMfoXAU=&PreviewHandout=bA==