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Immunity Nutrients At-A-Glance: Vitamin C

Published on: May 4 2020

What does Vitamin C do for the immune system?

Vitamin C is one of the most common nutrients that comes to mind when thinking about immunity. It is a water-soluble vitamin that serves as a cellular antioxidant, which means it protect cells from reactive oxygen species and cellular damage. This includes protecting immune cells from damage to allow them to function properly.

It has also been shown to stimulate production of white blood cells, which are a key part of the body’s innate and adaptive immune responses. Some leukocytes engulf and destroy pathogens, while other types of leukocytes are involved in antigen presentation to help the immune system identify and destroy threats.

Close up of orange slices

The innate immune system:When pathogens like infectious bacteria or viruses get into our respiratory tract or gastrointestinal system, the innate immune system responds by sending cells like neutrophils or macrophages to remove the threat. These cells attempt to swallow up the invading pathogen or create enzymes to destroy the pathogen.

The adaptive immune system is sometimes described as the ‘memory’ of our immune system. Once we are exposed to a pathogen, our immune system can remember the identity of that pathogen for the future and quickly mount a defense specific to that pathogen.

Do people get enough vitamin C?

Global daily recommendations range from 40 to 110 milligrams per day, depending on region. For example, in the United States, daily recommendations are 90 milligrams per day for men and 75 milligrams per day for women. In Europe, EFSA has established a 95 milligram per day Population Reference Intake.

About 20% of the global population is estimated to have inadequate intake of vitamin C, but the exact number varies depending on global region. For example, around 40% of the population of South Asia is estimated have inadequate intake of vitamin C, but the average intake of vitamin C in the United States is close to recommendations; 85 milligrams per day for men and 75 milligrams per day for women.

People who smoke or are exposed to second-hand smoke need more vitamin C in their diets because smoke increases the amount of vitamin C that the body needs to repair damage caused by free radicals. According to the National Institutes of Health (NIH), people who smoke need 35 mg more vitamin C per day than non-smokers.

Where can vitamin C be found in food?

Vitamin C can be found in many fruits and vegetables, such as kiwis, oranges, peppers and broccoli. The table below shows amounts of vitamin C found in common foods.

Sources of vitamin C

Source: National Institutes of Health Zinc Fact Sheet for Health Professionals

Do vitamin C supplements help with illness?

The exact way that vitamin C supplementation beyond normal daily values would improve immune function is not well defined. There is some evidence that vitamin C doses exceeding daily values could have potential benefit. A Cochrane review of clinical trials testing vitamin C’s effect on immunity found that regular supplementation (>200 milligrams per day) had a consistent effect in reducing the duration of common cold symptoms. On the other hand, vitamin C supplementation did not influence how often study participants got sick.

Additional resources

Immune System, What’s Your Function?

NIH Fact Sheet for Health Professionals: Vitamin C

Linus Pauling Institute’s summary of vitamin C

To learn more about how COVID-19 is affecting the food and beverage industry, including changes in consumer preferences and purchasing behaviours, visit Kerry’s COVID-19 resource page.

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