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Are Vitamins Making you SLOW?

Antioxidants and Endurance Training


Every day endurance athletes all over the world reach for their multi-vitamins or vitamin C tablets as part of their morning routine. Even if athletes are not supplementing with vitamin tablets they get their fair share via that added to sport drinks and gels by manufactures or through their daily diet.

So, “what’s the big deal, vitamins are good for you, aren’t they?”

To fully understand the issues antioxidants present to endurance athletes we need to get to know the main players: Free Radicals and Antioxidants.

Free Radicals

Free Radicals are molecules with one or more unpaired electrons which are highly reactive to other molecules. This reactivity causes a chain reaction of Free Radical production and these Free Radicals ‘attack’ surrounding cell DNA, proteins and lipid membranes. This damage can have an acute effect on the cell processes as well as a chronic damaging effect on the cells over time. This damage plays a key role in immune function suppression and the development of diseases such as cancer, arteriosclerosis, arthritis, neurodegenerative disorders and other conditions. Due to these damaging effects of Free Radicals and the increased production during exercise it is commonly recommended that Free Radicals are minimised through antioxidant supplementation to avoid these damaging effects.


Antioxidants are produced via the body as well as being obtained through that diet. Antioxidants ‘scavenge’ Free Radicals and ‘neutralise’ them minimising the damage they can cause. Common antioxidants include vitamins A, C and E. Anti-oxidants are most readily absorbed (bio-available) when eaten in ‘whole food’ rather than through supplementation with tablets.

The big picture

Oxidative stress is simply the balance between Free Radical production and the ‘neutralisation’ of these Free Radicals via antioxidants. i.e. the more Free Radicals present the higher the oxidative stress. Exercise increases the production of Free Radicals and the longer and harder the exercise is the greater the production so endurance athletes experience a large amount of oxidative stress during their daily training.

On the surface it would appear that endurance athletes would benefit from supplementing with antioxidants as this would decrease the oxidative stress and therefore the cell damage especially that suppressing immune function. However, the intake of antioxidants may be preventing athletes gaining the desired training benefit. The basic equation that I have talked about in earlier articles of

‘Training stress + Recovery = Improved performance’

can help us better understand the sometimes confusing topic of oxidative stress and endurance training.

When an athlete performs a training session they place a ‘training stress’ on their body, following the training session their body adapts to the specific ‘training stress’ so that when it next encounters this stress again it is better able to ‘deal’ with it or in the case of endurance sport go faster for longer. Numerous studies performed on rats and humans have shown that oxidative stress is an important ‘training stress’ to stimulate the body to make more mitochondria which are the power houses of the muscles. If oxidative stress is reduced through the consumption of antioxidants then one of the main training effects that you worked so hard to get is ‘undone’.

There are yet to be studies investigating the effect the timing of anti-oxidant intake in relation to training. However, to maximise the oxidative stress related training mechanism it would seem logical to avoid anti-oxidant supplementation or foods rich in anti-oxidants immediately before, during and after training. As with the carbohydrate ‘window of opportunity’ there is likely a ‘window of sensitivity’ following exercise when the body is most sensitive negative training effects of anti-oxidants. Without any hard evidence to support this it is hard to draw conclusions; however a recommendation of ~ 2 hours is a good starting point.

Antioxidants are important for your general health, so foods high in antioxidants need to be incorporated into an athlete’s diet without hampering their training adaptations. Before the additional supplementation of any micro-nutrient (i.e. vitamins or minerals) a deficiency should be identified via a medical professional.

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Practical advice

Times to avoid antioxidants to maximise training adaptations

  • Immediately before, during and in the two hours post training

  • During endurance focused and high intensity training blocks

Times to consume antioxidants as to minimise impact on training adaptations while maintaining health

  • On days/ training phase when your focus is on technique or tactical aspects

  • On recovery days

  • During recovery weeks when the focus is on rest and recovery

  • When you are feeling overly run down, tired or ill (combined with a decrease in training duration)

  • In the lead up to races and during races

Final thought

While consuming antioxidants during or following a training session is not going to fully suppress the training adaptations of a session there will be a small decrease. Over the multiple training sessions this small difference between the optimal training stimulus and the small suppression is going to add up to a potential big difference between what is and what could have been in the long term. With this in mind reviewing your antioxidant intake could be well worth your while.


Ristow, et al. (2009). Antioxidants prevent health-promoting effects of physical exercise in humans. Proc Natl Acad Sci U S A, 26; 106, 8665–8670.

Gomez-Cabrera, et al. (2008). Oral administration of vitamin C decreases muscle mitochondrial biogenesis and hampers training-induced adaptations in endurance performance. Am J Clin Nutr, 87, 142-149.

Di Meo, S., & Venditti, P. (2001). Mitochondria in Exercise-Induced Oxidative Stress. Biol Signals Recept 10, 125-140.

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