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Vitamin C & Immunity

Vitamin C, also known as ascorbic acid, is an essential water-soluble nutrient found in lots of fruits and vegetables. It plays an important role in immunity mainly due to its antioxidant capacity, antimicrobial and antiviral actions. Vitamin C occurs in high concentrations in leucocytes but during a common cold, the levels fall dramatically when oxidative stress increases. Vitamin C is a scavenger of these reactive oxidative species and hence can reduce excessive tissue damage during an infection. 

Deficiency is uncommon, but boosted levels can bolster immune function, and decrease infection risk. Research has shown that regular supplementation with Vitamin C helps reduce the duration of the common cold as well as the severity of its symptoms. Up to ~50% reduction of the incidence of URTI’s has been seen in those who exercise heavily, when oxidative stress increases, while supplementing with Vitamin C.  

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The best dietary sources of Vitamin C include, but are not limited to, citrus fruits, tomatoes, potatoes, red and green peppers, kiwifruit, broccoli, strawberries, brussels sprouts, and cantaloupe/rockmelon. The recommended daily intake (RDI in Australia) is 45mg daily for the general population.

Vitamin C in foods and in supplementation form is safe at intakes up to 1,800 mg/day for children, depending on age, and up to 2,000 mg/day for adults. Chronic megadoses (<1g) can have a cellular blunting effect on training adaptations that athletes strive to gain for performance improvements.

The potential benefit of Vitamin C supplementation on reducing the incidence of upper respiratory track infections during heavy training periods, or travel, needs to be weighed against the facts around regular intakes of megadoses (<1g) that can have negative performance effects.

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