Can vitamin C be used to support exercise? And what happens if we take too much?

What is Vitamin C?

Vitamin C is a water-soluble antioxidant vitamin that acts in numerous biochemical reactions in the body. Vitamin C plays important roles within enzymes involved in collagen biosynthesis (required for connective tissues). Vitamin C also aids in iron absorption. A deficiency is rare given due to the high content of fruit and vegetables. The current NRV for vitamin C is 80mg and is more than achievable with 5 fruit and veg a day.

What Does Vitamin C Do in the Body?

As an antioxidant, vitamin C reacts with potentially damaging reactive oxygen species (ROS) and has been shown to protect plasma lipids (fats in the blood) against oxidative damage. It also strengthens the antioxidant network in cells by helping to maintain vitamin E levels.  Vitamin C may enhance immune function and through enhancement of immune cell function. Vitamin C supplementation may be able to prevent and treat respiratory and systemic infections.  It may therefore have benefits for athletes undertaking intense exercise which can make infection more likely.

Taking Vitamin C for Exercise

During exercise, our muscles produce increased amounts of ROS. Excess ROS can promote damage to proteins, lipids, and DNA, and potentially impair physical performance, recovery, and immune function.

Vitamin C supplements may act to neutralise some of the damaging effects of exercise-induced ROS. A scientific review found that regular vitamin 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.

Too much Vitamin C

Although super high doses are commonly consumed by the general population, a daily total dose of between 500-1000 mg supplemental vitamin C may only be safe to consume acutely (during illness) to support immune health for most athletes undertaking intense exercise.

There is compelling evidence to suggest chronic ingestion of single high dose antioxidants such as 1000 mg per day for 8 weeks can impede training adaptations, yet when the same amount of Vitamin C is ingested via whole food sources, performance may actually improve. Collectively this supports a food first approach to achieving Vitamin C intake if you can, except for a short period during illness.