Various antioxidants, such as vitamin C, are very popular among physically active people. It has been previously shown that vitamin C supplementation during intense exercise helps prevent colds, (1) but how it affects athletic performance itself or muscle growth is still questionable.

Much research has looked at vitamin C in combination with vitamin E, as both are an important part of our body's antioxidant system. In addition, vitamin C can help recycle vitamin E, which significantly increases its effectiveness. However, the disadvantage of studying them together is that it is difficult to determine their significance separately.

Most of the studies have looked at such unnaturally high doses of vitamin E as would be impossible to obtain from food, and often the synthetic form of dl-alpha-tocopherol acetate was investigated, which is different from the naturally occurring vitamin E. This is important because over-supplementation with vitamin E has been shown to cause adverse effects in the past, whereas supplementation with a realistic amount has generally been beneficial.

Do antioxidants improve or impair physical performance?

In the short term, intense exercise increases oxidative stress and inflammation, which can be reduced by various antioxidants. Some theorize that this can speed up recovery, which is beneficial for sports performance, but some see it the other way around.

The opposing view is that increased oxidative stress and inflammation are necessary for proper adaptation after exercise, and reducing them may impair physical performance and inhibit muscle growth in the long term.

The idea that antioxidants can inhibit post-workout development is strange, seeing as almost all natural foods contain antioxidants, and our bodies are constantly producing them. It is, therefore, almost impossible not to consume them, and their levels can only be significantly reduced by methods that are very unhealthy in other ways, such as inducing a deficiency in a micronutrient.

The effect of vitamins C and E on strength levels

A 2022 meta-analysis of pooled results from 18 randomized trials found that supplementation with vitamins C and E reduced lipid peroxidation, cortisol levels, and certain inflammatory markers but had no significant effect on muscle soreness and, more importantly, muscle strength. (2) Two 2020 meta-analyses also found that combined supplementation with vitamins C and E had no significant effect on strength. (3,4)

So, they do not improve physical performance, but they do reduce several of the deteriorative processes that can lead to serious health problems over time, so they are worth supplementing for general health maintenance. 

No athlete should fear that these vitamins will hinder their development, but neither should they be expected to improve performance significantly. They may be of minor importance: if a person is less likely to fall ill as a result of vitamin C supplementation, this will improve performance in the longer term.

Effect of the two vitamins on muscle growth

When looking at the results in aggregate, the use of vitamins C and E is not significant for muscle growth (3,4) but when looking at the studies individually, there are some interesting findings.

In a 2016 randomized trial, combined supplementation of the two vitamins reduced muscle growth in elderly individuals in combination with a resistance training program. (5) Participants supplemented 500 mg vitamin C and 117 mg vitamin E immediately before and after exercise for 12 weeks and after 3 months were assessed for strength and muscle gain. The people who did not supplement with vitamins had a 3.9% increase in lean body mass, while the other group had a weight gain of only 1.4%. These results might suggest that vitamin supplementation was harmful, but interestingly there was no difference in strength levels between the two groups.

Back in the day, Paul Jaminet, author of The Perfect Health Diet, came up with an interesting theory: supplementing with antioxidants reduced inflammation in stressed muscles, so they grew less, but given that they gained the same amount of strength, they ended up with smaller but much healthier muscles.

In two previous studies, older people have shown a marked benefit from combined vitamin supplementation in terms of muscle growth. Members of the placebo groups did not gain muscle despite resistance training, whereas those taking vitamin C and E supplements showed significant muscle growth over 6 months. (6,7)

In conclusion, supplementing with vitamin C or vitamin E will not hinder anyone's muscle growth, and, in fact, for older people - who generally have poorer antioxidant status - it can be a particularly useful supplement.

What about endurance sports?

The results are similar here: a 2020 meta-analysis of several human clinical trials found that supplementation with vitamins C and E has no effect on endurance exercise performance and does not impair adaptation. (4) Endurance capacity as measured by VO2max is also not significantly affected. (4)

Some studies have observed changes in metabolic processes that may play a role in endurance performance as a result of vitamin supplementation, but this has not yet been confirmed by studies. (8,9,10)

Summary

Albeit we may occasionally come across the theory that vitamins and certain antioxidants can hinder our development during physical exercise, no such effect has yet been proven. Even if it exists, the magnitude of the effect is so small that it is not worth bothering about.

In contrast, elderly or intensively exercising individuals may benefit from vitamin supplementation because of other health effects. Unless there is a specific reason to do so, do not supplement more than 100 IU of vitamin E per day, with about half of this amount coming from alpha-tocopherol.