Does vitamin C block gains from training?


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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.

So which is true? Back in 2009, a German study found that vitamins C and E did indeed block gains in insulin sensitivity — a key adaptation to exercise — in a group of sedentary volunteers. But in January 2010, a study of cyclists found no difference in fitness parameters like maximal oxygen consumption, power output, lactate threshold and so on between a placebo group and a vitamins C/E group. But then last December, a study with rats found that vitamin E did block gains in mitochondria, a key adaptation to endurance training.

Which brings us to the most recent study, published in March in the International Journal of Sports Physiology and Performance. A total of 17 recreational runners did a four-week training program consisting of four interval workouts a week (5x3min hard with 3min jog recovery — a bit of an odd program, but it succeed in significantly boosting VO2max, running economy, 10K time trial performance, etc.). Half the subjects took 1 gram of vitamin C every morning, while the other half took a placebo; the trial was double-blinded, so no one knew who was in which group. The results: no significant differences between the groups.

So where does this leave us? I’m not really sure. The paper discusses a couple of possible explanations. One is that antioxidants do block some training gains but that this study was too small to detect them. With nine subjects in one group and eight in the other, that’s certainly possible. For example, the subjects ran two  “YoYo Intermittent Recovery Tests” with slightly different parameters. In the first one, the vitamin C group improved 22% while the placebo group improved only 16%; in the second one, it was the other way around, with the placebo group improving 10% and the vitamin C group improving only 5%. This doesn’t give me a whole lot of confidence in the test-retest variability, or the ability to detect subtle differences in adaptation.

Another possibility relates to the initial fitness of the subjects. The 2009 German study used sedentary, unfit subjects, who thus would be expected to produce very high levels of ROS in response to the unfamiliar stress of exercise. In these subjects, one might expect antioxidant supplements to make a bigger difference to training adaptations. The new study, on the other hand, used subjects with higher initial aerobic fitness (“recreationally active,” not trained athletes). As the saying goes, “exercise is the most powerful antioxidant we have.” So it’s possible that fit subjects already have reasonably effective natural antioxidant defenses in place, so taking additional antioxidant supplements doesn’t make as much (or any) difference.

All of this leaves us with no firm answer — as usual, more studies are needed. My guess (thinking back to my last post about the pros and cons of training on empty) is that we’ll eventually conclude that the answer is “it depends.” Perhaps antioxidant supplements will be helpful during extremely heavy training blocks, but should be avoided as you approach competition. Or perhaps it’s the other way around: let the ROS run wild during heavy training blocks, but take antioxidants to ensure full repair as competition approaches. The latter approach fits with a Portugese study that found that antioxidants may delay muscle repair after heavy workouts, but could allow muscles to actually work harder in the heat of competition. It’s too soon to know for sure.

12 Replies to “Does vitamin C block gains from training?”

  1. I find this an interesting concept that I was introduced to a few months a go. In theory it makes sense that antioxidant could potentially decrease training adaptations that are mediated through ROS. Although the methodology is all over the place in the studies and results are inconclusive, I wonder if natural sources of antioxidants would have effects. My guess is that a healthy diet full of antioxidant rich vegetables and fruit (not requiring supplements) will not prevent training adaptations, but who knows!
    This definitely is information applicable to elite athletes where a minute increase or decrease in performance determines their fate. We don’t need another reason for the average joe to be avoiding antioxidant rich foods!

  2. Hi Alex,

    Hope you are well. Will you be coming out to Calgary again for the Scotiabank marathon?

    In a lot of the studies exercise physiology you see very positive fitness results from one-dimensional training plans on sedentary or beginner runners. (For example the plan in this article is 4 days/wk of 5 x 3 on intervals.) Are there any studies that compare the actual training plans people use? For example, a Runner’s World 10k plan vs. Brad Hudson’s approach vs. Lydiard. Alternatively, are there any studies that compare a standard training plan with the one dimensional ones so often used in studies? (Ie the Runner’s World 10k plan vs. a tempo run every other day).


  3. Would you happen to know where I can find a more detailed explanationfor the non-expert of the ‘Vitamin C blocks gains’ theory ? Somehow it doesn’t square with my -admittedly very limited- knowledge of vitamins.

    I was taught in high school that vitamin C has a typical threshold effect, below which you have deficiency diseases and above which additional amounts are secreted in your urine. Wouldn’t it be possible that a normal diet contains enough vitamin C and that most studies effectively compare two groups of athletes with enough vitamin C ?

    Secondly, as I understand, the body has to maintain a balance between antioxidant and ROS, otherwise it would kill the messenger before the message is delivered. If vitamin C were the only antioxidant available, I can imagine that heightened ROS due to exercise and no additional Vitamin C would mean lots of signalling and could thus encourage a speedier repair. However, there are more antioxidants than vitamin C. Couldn’t it be that having low amounts of vitamin C relative to the amount of ROS simply causes a resort to other antioxidants?

    Two vital steps in the theory seem to be that more ROS in the bloodstream cause a more massive or more effective repairing response instead of mobilizing more antioxidants, and that this response itself is somehouw trainable. Is there any specific science (understandable for the layman) on that?

  4. Lots of interesting comments here — sorry it’s taken me so long to get back to them.

    @Danielle: I agree. I have no hesitation in saying everyone, including athletes, should be eating as much fruit and vegetables as they can. It’s possible that antioxidants don’t have the same (hypothesized) negative effects in fruit as they do when isolated in supplements; it’s also possible that the benefits offered by fruits and vegetables are simply much greater than any possible downside caused by antioxidants. We don’t really know, but there’s definitely no justification for cutting down on fruit and veg.

    @Jason! Long time no talk — to my great regret, I’m going to miss Calgary this year, because I need to be in Ottawa. Are you running?

    As for your question, it’s an interesting one. I can’t think of any examples of the type of study you suggest. So lots of people love, say, Jack Daniels’ training plans, and Jack Daniels has certainly done lots of research — but those two things have never been combined (to my knowledge). There’s no study comparing the Daniels approach to some other plan for a group of runners preparing for an actual race.

    I think part of the problem is that most sports science research funding is actually funneled through “health” agencies. So even when researchers are interested in performance, the grants they get have to be written in the context of effective ways to boost aerobic fitness in order to lower risk of cardiovascular disease or whatever.

    The other, deeper problem is that training is so unbelievably complex that it’s hard to make any GENERAL conclusions by comparing two groups where a whole bunch of variables are different. If you take two standard training plans, they may have different mileage, intensity, workout frequency and so on — and within the workouts themselves, the possible details of which intervals to run, how fast, and with how much rest are endless. Even if one group performs better than the other at the end of the study, we don’t know why, and whether the same would hold true for another group. Was it because one group did lots of tempo work that improved lactate clearance? Or was it simply because the other group did less mileage? Runners would be interested in the results regardless, but it wouldn’t get published in a good journal, so it would be a bad career move for the researcher.

    Instead, researchers try to hold everything constant except for one variable. That gives them insight into how the human body responds to different stimuli — but it means that the actual training used by real runners is almost entirely based on the trial and error of the last half-century, rather than any science.

    Bottom line (sorry for the long-winded answer!): I’d love to see a study like you suggest, but I think the way current sports science is structured, it’s unlikely.

  5. @RH
    Let me start with the last question, about whether the exercise->ROS->antioxidant response is trainable. This paper (“Moderate exercise is an antioxidant: upregulation of antioxidant genes by training”) was a big one:

    For a more general review of the “oxidative stress promotes health” theory, here’s a review by Michael Ristow (the guy who did the famous study where people exercising and taking antioxidants didn’t improve their insulin sensitivity as much as those just exercising):

    I, too, was taught that too little vitamin C leads to scurvy and too much is just peed out (Linus Pauling’s ideas notwithstanding). But I think it’s now pretty clear that vitamin C is one example of (as you point out) a larger class of molecules (antioxidants) that do SOMETHING (the details of which still aren’t clear) in the body. I think the experiments trying to show that large doses of vitamin C are good (for the immune system, e.g.) or bad (for training adaptations) rely on significantly increasing the overall levels of antioxidants in the body, not just the levels of vitamin C. Most of the studies, in fact, administer a cocktail of different antioxidants.

    Anyway, I’m sure this doesn’t really answer your questions, but hopefully one of those papers might have some clues (if you’d like the full-text versions, just let me know).

  6. Thanks! That does answer all my questions, namely with “it is not as simple as that!”

    I am way beyond my depth here, but as far as I can understand, it is a delicate balancing act between (among others) ROS on the one hand and both nutritional antioxidants as vitamin C and antioxidative responses produced by the body itself. Apparently relying on the antioxidative response of the body itself produces longevety and certain enzymes associated with training adaptations. As if one balancing act was not enough, you do need vitamin C for other purposes (and perhaps even more, the more you exercise).

    I´d be interested in a full text version of the first article, if it is no trouble.

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