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What is it?

  • Vit. C is a water-soluble antioxidant vitamin that acts as an electron donor for numerous biochemical reactions in the body. Vitamin C plays important roles as a cofactor for enzymes involved in collagen hydroxylation, plus carnitine and catecholamine biosynthesis. Vit. C also aids in iron absorption. A deficiency of Vit. C is rare given relatively low recommended dietary intake (45 mg per day) and wide distribution in fresh fruit and vegetables.
    • As an antioxidant, Vit. C reacts with potentially damaging reactive oxygen species (ROS) and reactive nitrogen species (RNS) and has beenshown to protect plasma lipids against oxidative damage.1 Vit. C also strengthens the cellular antioxidant network by helping to maintain Vit. E and glutathione levels.2-4
    • Vit. C is very labile and thus content in food varies according to season, transport, shelf life and storage time, cooking practices and chlorination of water. Cutting, bruising, heating and exposure to copper, iron or mildly alkaline conditions can destroy ascorbate. It can also be leached into water during cooking.5
  • Vit. C may enhance immune function through effects on epithelial barriers, white blood cells and inflammatory mediators.6 Through enhancement of immune cell function, Vit. C may be able to prevent and treat respiratory and systemic infections.6 Vit. C supplements are promoted to reduce the duration and severity of colds, although the evidence supporting this is mixed:
    • Vit. C supplementation (200-2000 mg per day) has been found to reduce the duration of the common cold by 8% and reduce the severity of cold symptoms.7 Neither acute nor chronic Vit. C supplementation influences the incidence of upper respiratory tract infections.
    • Some studies in military personnel and school boarders have found a reduction in incidence of pneumonia by 80-100% with Vit. C supplementation8, although findings of these studies cannot be extrapolated to other groups.
  • Vit. C may have benefits for athletes undertaking intense exercise. During exercise, our muscles produce increased amounts of ROS and RNS. Excess ROS and RNS can promote damage to proteins, lipids, and DNA, and potentially impair physical performance, recovery, and immune function. Vit. C supplements may act to neutralize some of the damaging effects of exercise-induced ROS and RNS, although studies report mixed findings on exercise-related outcomes:
    • A systematic review found that regular Vit. C supplementation (250-1000 mg per day) reduced the risk of the common cold by over 50% in athletes such as marathon runners and skiers who are exposed to short periods of extreme physical stress.7
    • Some evidence from randomized controlled trials indicate Vit. C supplementation (500-2000 mg per day) can prevent exercise-induced bronchoconstriction.9
    • Studies of effects of Vit. C supplementation on muscle function following a bout of intense fatiguing exercise have yielded mixed findings10-15, drawing into question its use for recovery of muscle function.
    • There is compelling evidence to suggest chronic ingestion of single high dose antioxidants such as Vit. C (1000 mg per day for 8 weeks) can impede training adaptations16, yet when the same amount of Vit C is ingested via while food sources, performance may actually improve.17 Collectively this supports a food first approach to achieving Vit. C and other antioxidant nutrient needs, except in unique circumstances

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