The case against antioxidant vitamin supplements


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- Alex Hutchinson (@sweatscience)


The December issue of Sports Medicine has an enormous, detailed review of research on the effect of antioxidant (i.e. vitamin C, vitamin E, coenzymeQ10, etc.) supplements on training. To most people, this seems like a no-brainer: what could be smarter than popping a multivitamin as “insurance” in case your diet isn’t giving you all the vitamins you need? But (as I’ve blogged about before) there’s an emerging school of thought arguing that taking antioxidants can actually block some of the gains you’d otherwise get from training. Here’s how I explained the debate back in April:

The traditional theory goes like this: strenuous exercise produces “reactive oxygen species” (ROS), which cause damage to cells and DNA in the body. Taking antioxidant supplements like vitamins C and E helps to neutralize the ROS, allowing the body to recover more quickly from workouts.

The new theory, in contrast, goes like this: strenuous exercise produces ROS, which signal to the body that it needs to adapt to this new training stress by becoming stronger and more efficient. Taking antioxidant supplements neutralizes the ROS, which means the body doesn’t receive the same signals telling it to adapt, so you make smaller gains in strength and endurance from your training.

The new paper comes down firmly on the side of the latter view:

The aim of this review is to present and discuss 23 studies that have shown that antioxidant supplementation interferes with exercise training-induced adaptations. The main findings of these studies are that, in certain situations, loading the cell with high doses of antioxidants leads to a blunting of the positive effects of exercise training and interferes with important [reactive oxygen species]-mediated physiological processes, such as vasodilation and insulin signalling.

So is this definitive? Far from it. As the review notes, there have been a few studies that found beneficial effects of antioxidant supplements on exercise performance, tons that have found no effect, and a few (23, to be exact) that have found negative effects. What most of the studies have in common:

As commonly found in sports nutrition research, the vast majority do not adhere to all the accepted features of a high-quality trial (e.g. placebo-controlled, double-blind, randomized design with an intent-to-treat analysis). Indeed, most studies fail to provide sufficient detail regarding inclusion and exclusion criteria, justification of sample size, adverse events, data gathering and reporting, randomization, allocation and concealment methods, and an assessment of blinding success. The poor quality of the majority of studies in this field increases the possibility for bias and needs to be always considered when evaluating the findings.

This is a really important point to bear in mind, and not just when it comes to sports nutrition. Whatever the supplement, training method, or piece of equipment you’re talking about, there’s nearly always a crappy, poorly executed study that seems to “prove” that it works. So where does that leave us? On this topic, I’m in agreement with the authors:

We recommend that an adequate intake of vitamins and minerals through a varied and balanced diet remains the best approach to maintain the optimal antioxidant status in exercising individuals.

15 Replies to “The case against antioxidant vitamin supplements”

  1. I really enjoy reading all of the posts that you write, especially because I find that you take a very balanced approach to the science of exercise.

    My question has less to do with this specific study and more so with what this article (and many of your posts) clearly acknowledge — that it’s more common to have poorly-designed sports science/nutrition research than it is to have well-designed research. As a consequence, we get results which are of questionable value (in terms of practical application or building scientific knowledge) and which only serve to further obfuscate many key issues when interpreted by the public (often via various media outlets).

    These studies take time and money to complete. Because they involve human subjects, I assume they are reviewed by IRBs and other design review boards. Why, then, do we continue to put resources into them? And how do we get to the point where the studies being conducted provide consistently meaningful data either for researchers or athletes?

    Thank you again for your great work.


  2. Alex, this is the type of post I was hoping you would eventually make, obviously you written on antioxidants before with a similar conclusion; that one should have a varied and balanced diet.
    My step father is always advocating a supplement called Usana that promotes very very high dosages of minerals and antioxidants. I can’t seem to convince him that the anecdotal evidence that he’s ‘never’ been sick while on their product does not mean that it’s as healthy as the company proposes. As an aside, my mother and step father already eat what I would call a healthy diet, so there’s that too…
    We’ve emailed Usana only to have them discount articles that you’ve referenced citing them as biased, claiming that the authors have a vendetta against supplements, etc. It all seems pretty silly when you consider that their support for supplements is at least on the outset more biased than any reporters, they’re selling a product after all.

  3. Where does the “timing” of taking antioxidants, Vitamin C, etc, come into play? Is there a time window before or after training to take them?

    Coach OB

  4. Enjoyed reading this post, as I find many people (athletes and non-athletes alike) are drawn in by erroneous &/or exaggerated claims made by supplement companies. Anecdotal evidence is not scientific proof. Be skeptical….if it sounds too good to be true it probably is!

  5. Thanks for the comments, folks.

    @Coach OB: I don’t know of any reasons to take antioxidants at a particular time of day. One way of interpreting the latest research is that you might want to periodize intake on a yearly/seasonal basis: avoid antioxidant supplements during heavy training periods (where the main goal is adaptation), but take them during tapering and competition periods (where recovery is the main goal).

    @Eric: Good questions, no simple answers. In terms of why “we” continue to put resources into crappy studies — well, that depends who “we” is. Companies that make supplements (or other health products) continue to fund crappy little studies in the hopes of getting “scientific evidence” that they can use to sell their products. Better to fund 10 crappy studies and eventually get one that produces the “right” result than to put all those resources into one big, properly designed study that may well conclude that their product is useless. (On a less nefarious level, it’s also much easier for these companies to put aside a bit of money for occasional small studies than it is to commit a big chunk of cash to a multi-year research project.)

    Also, many studies are produced in academia, and they’re often produced by master’s students who have barely more than a year to design a study, find participants, collect data, analyze it and publish the results. So you get all these studies with 10 subjects and one outcome measure. It’s very difficult to find the resources — money, researchers, subjects, etc. — to undertake a study that will take several years to complete.

    What’s the answer? I don’t know other than to continue to demand better, and refuse to believe hype based on inadequate evidence.

  6. I wonder if the antioxidant dynamic might depend as well on the degree of training vs over-training. I could be way off base but if training is below a certain threshold perhaps the body can adapt on its own and antioxidants would interfere to some degree with those adaptations.

    If overwhelmed beyond its ability to adapt however I wonder if antioxidants might be supportive or protective to some degree?

    This seems to me like finding the right balance between training hard enough to stimulate adaptation (but not over-training) and eating healthy to help recovery and provide some free radical protection (but not taking tons of supplements).

  7. 6 weeks ago I decided to do my own personal experiment and ceased intake of vitamin pills. I haven’t experienced any noticeable change in cycling performance since doing this (as measured with a power meter). I did, however, feel absolutely terrible for the first few days, even though my cycling performance was unaffected.

    I can think of two possible reasons for this:

    1. It may be possible to do a sufficient amount of training that even with the reduction in adaptation from consuming anti-oxidants, you are still maxing out the body’s ability to adapt. A study to investigate this would need to have multiple groups doing a range of training volumes, to see if there is a training volume above which those who aren’t consuming anti-oxidants gain no further adaptation, but those are consuming them do.

    2. Anti-oxidants may only reduce the rate of adaptation rather than the eventual total adaptation. I.e. you get there quicker without anti-oxidants, but eventually end up in the same place either way. A study to investigate this would need to have a much longer duration to see if the people consuming anti-oxidants continue to adapt when those not consuming anti-oxidants have reached a stable level of adaptation.

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  9. I am a researcher studying reactive oxygen species (ROS) and according to our labs findings, ROS is essential for the body to heal after a heavy workout. The reason why there is a spike in ROS after a workout is because the mitochondria goes into full swing, producing lots of ATP. These ROS have beneficial roles and hence taking antioxidants right after exercising would be foolish because they quench the beneficial ROS. If possible, read research papers by Micheal Ristow(who proved that antioxidants after exercise are bad -PNAS paper and Barry Halliwell who proves that antioxidants are not as beneficial as claimed).

    Taking vitamin supplements would not be recommended on a daily basis but i’d rather suggest that people take them once or twice a week and that too only if they have not had healthy food(fruits and vegetables)

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