Antioxidant and Vitamin D Supplements for Athletes: Sense or Nonsense? – Research Review

Powers S et. al. Antioxidant and Vitamin D supplements for athletes: Sense or nonsense? J Sports Sci. 2011  Aug 11. [Epub ahead of print]

The idea that dietary supplements can improve athletic performance is popular among athletes. The use of antioxidant supplements is widespread among endurance athletes because of evidence that free radicals contribute to muscle fatigue during prolonged exercise. Furthermore, interest in vitamin D supplementation is increasing in response to studies indicating that vitamin D deficiency exists in athletic populations. This review explores the rationale for supplementation with both antioxidants and vitamin D and discusses the evidence to support and deny the benefits of these dietary supplements. The issue of whether athletes should use antioxidant supplements remains highly controversial. Nonetheless, at present there is limited scientific evidence to recommend antioxidant supplements to athletes or other physically active individuals. Therefore, athletes should consult with their health care professional and/or nutritionist when considering antioxidant supplementation. The issue of whether athletes should supplement with vitamin D is also controversial. While arguments for and against vitamin D supplementation exist, additional research is required to determine whether vitamin D supplementation is beneficial to athletes. Nevertheless, based upon the growing evidence that many athletic populations are vitamin D deficient or insufficient, it is recommended that athletes monitor their serum vitamin D concentration and consult with their health care professional and/or nutritionist to determine if they would derive health benefits from vitamin D supplementation.


Supplements for athletic performance have been a part of the landscape for decades and athletes are always looking for an edge in terms of either promoting adaptations to training, recovery, or outright performance.    And while many in the field tend to think of me as anti-supplement, this really sort of misses my issue with supplements.  Because I’m not anti-supplement; rather I’m simply anti-bs.

I’m also anti-anything that takes focus away from the factors that actually do matter, namely things like training, diet, lifestyle, etc.  And the sad fact is that all too many athletes try to use supplements in place of proper training, attention to their diet, etc.  It goes to something I discussed ad nauseum in the thankfully finished Why the US Sucks at Olympic Lifting series, quick fixes are more appealing than things that take work.  And popping a pill is easier than working your nuts off in the gym or watching your diet.

And the reality is that most claims made for most supplements are about 99% bs and 1% “Well, maybe”.   Of course, that never stops athletes, who fall prey to the logic of “IF this is the next big thing, I don’t want to miss out on it.”  Of course, supplement industries pander to that very thought process; that’s how they make shocking amounts of money off of desperate athletes.

I’ve been in this field for over 2 decades and in that time I’ve seen thousands of products come and go, always with the same hype and exciting ad copy claiming that they are the solution for the woes of athletes, only to disappear months later to be replaced by the newest crop of crap.  Because over that 20 years, I can count the number of products that even came close to living up on maybe two hands.  That gives supplements about a 99.9% failure rate; in my mind it’s absurd to hold any opinion about anything new except to assume it’s crap until proven otherwise.  But I’m sort of getting off track here and really only want to focus on two specific supplements since they relate to today’s paper.

Because for about three decades, one ‘class’ of supplements that has been popular (and very often recommended) is that of anti-oxidants.  In short, these are compounds that help to scavenge or ‘deal with’ what are called reactive oxygen species (ROS) in the body. These are produced under various conditions (including exercise) and one early theory of aging and bodily damage was that the production of ROS was part of the overall breaking down of the body.  With the logical solution being to simply take these nutrients in doses ranging from reasonable to ‘Oh my god, you want me to take how much?’ levels.  I can fondly remember Colgan and his laundry list of high-dose anti-oxidants in Optimum Sports Nutrition (an excellent book so long as you ignore every word about supplements) for example.

More recently, there has been great interest in Vitamin D status, both from a general health standpoint (Vitamin D deficiency is literally being considered a current vitamin deficiency epidemic and there is actually a staggering amount of data that this is the case) and from an athletic standpoint (and data going back to the 1920’s actually suggested this very early on).  Vitamin D does about a million and one things in the body but one thing it is strongly related to is muscular function and performance; I even mentioned explicitly in the Why the US Sucks at Olympic Lifting that one advantage that Kenyan runners may have is the ability to train outdoors year round (the same holds for Jamaican sprinters) and this may maintain better Vitamin D status compared to athletes who live in harsher environments.

Which is all just a lead up to today’s paper, a relatively short review on both anti-oxidant and Vitamin D (and calcium) supplementation for athletes, looking at the role that they play in the body and arguments both for and against the use of either by athletes.


The Paper

The paper starts by looking at the role of antioxidants in the body.  As I mentioned above, ROS are produced in the body under a variety of conditions including exercise and there is at least some evidence that ROS may cause fatigue during exercise when they are produced in large quantities; this is along with potentially causing overall bodily damage through oxidative stress (also caused by things like pollution and smoking for example) and muscle damage.

And this provided the idea that providing supplemental anti-oxidants (which include but are not limited to compounds such as Vitamin A, Vitamin C, Vitamin E, beta-carotone and a host of others; the list of potential anti-oxidant compound seems to grow daily).  However, with the exception of N-Acetyl Cysteine, which appears to reduce fatigue during some types of submaximal exercise (and it’s thought that this occurs by reducing ROS fatigue in breathing muscles, believe it or not), most studies supplementing anti-oxidants have not found any impact on performance.

Even the studies on anti-oxidant supplementation on muscle damage and oxidative damage are pretty mixed, probably reflecting differences in the type, amount and intensity of exercise along with the specific anti-oxidants and doses that were supplemented.  Basically, outside of NAC and submaximal endurance performance, the data is far from conclusive.

Moving to arguments for anti-oxidant supplementation, the paper examines three potential reasons that athletes might consider anti-oxidant supplementation.  First is the known increase in ROS production during activity, coupled with the general principle that the compounds are pretty much non-toxic even at relatively high levels. This is sort of a ‘It probably won’t hurt and might help’ kind of argument.  Kind of weak.

A second argument has to do with the role of excessive ROS on muscle fatigue but, as I noted above, with the exception of NAC, most supplementation studies have shown no performance benefit of anti-oxidants so this argument pretty much fails.  The final argument that they address is the idea that many athletes have poor or insufficient diets (note that most anti-oxidants in the diet come from fruits and vegetables) and that an athlete who’s diet is poor may need supplementation.  Which is equally weak for a number of reasons I won’t go into just yet.

In terms of arguments against anti-oxidants, the paper examines a number of arguments against supplementation. First they point out that while exercise certainly does increase ROS production it’s very transient (and this does distinguish it from the pollution or smoking examples which may be generating more chronic levels).  As well, the body already has an in-built system to deal with ROS production; quite in fact it increases it’s activity with training.

That is, by exposing the body to ROS in moderate amounts, it adapts by being better able to handle further ROS production (some have even theorized that high-dose antioxidant supplementation might be harmful down the road by limiting the body’s upregulation of it’s inbuilt system).

In a related vein, there is considerable evidence and this has been accumulating for a while that the production of ROS is part of the overall adaptation to training (and the data here is more geared towards endurance athletes than strength/power athletes).  That is, the production of ROS, like inflammation and a whole host of other things that occur with training appear to be part of the overall training stimulus; blocking this with high-dose supplementation could conceivably limit the adaptations to training.

Finally is the simple fact that studies are routinely showing that individual anti-0xidant supplementation (as opposed to diets high in natural anti-oxidants; that is diets including lots of fruits and vegetables) either have no real benefit to health or may actually be harmful and increase mortality in the long-term.    The authors conclude that outside of ensuring a mixed, energy sufficient diet (which should provide adequate ‘natural’ anti-oxidants) that there is no reason for athletes to supplement with individual high-dose anti-oxidants.  I’ll come back to this when I wrap-up below.

Moving on the authors next address Vitamin D along with calcium (since it’s a bit tough to separate the two).  Vitamin D is a bit odd among the vitamins for a number of reasons, not the least of which that it can actually be produced by the body specifically in response to sun exposure.  The authors overview the metabolism of Vitamin D but I won’t repeat that here, go Wikipedia it if you must know.

Vitamin D is critical in the body for a number of reasons, not the least of which is bone health; in this vein, adequate Vitamin D status is required for optimal calcium absorption in the body.  As well, Vitamin D regulates genes all over the body, controls inflammation and immune system function; a great deal of research has focused on low Vitamin D status and colon cancer.   Of more relevance to athletes is that Vitamin D status is tied to muscular function and Vitamin D is involved in the expression of a number of genes involved in muscular function and performance; all issues relevant to athletes.

There’s actual a considerable history of evidence on the issue of Vitamin D and performance although it’s only recently that researchers have realized that Vitamin D might be playing a role.  Let me explain: back in the early part of the 20th century, it was observed that athletes often made less progress during the winter months in terms of strength or performance and that exposure to ultraviolet light improved trainability and strength gains.  We now clearly know that UVB exposure would have had one effect of increasing Vitamin D synthesis in the body and as discussed in Athletic Performance and Vitamin D, this may have been the mechanism at work.

Of more relevance, recent research is finding that almost everyone is Vitamin D deficient, all over the world. This is due to a number of factors including things like overuse of sunscreen, working indoors, poor diet, etc.  Both calcium and Vitamin D come from the diet (and many foods are fortified with both) but, as I mentioned, Vitamin D is an oddity among the vitamins in that it can be produced by the body, specifically in response to direct sun exposure.

Moving to Vitamin D status, the authors point out that determination of optimal level of Vitamin D in the body is still a bit of a controversial area.  It’s generally considered that Vitamin D levels below 50 nmol/L (or 20 ng/mL) is a sign of deficiency while levels below 80 nmol/L (32 ng/mL) is insufficient.  What level is optimal is harder to determine but a concentration of 100-250 nmol/l (or 40-100 ng/ML) is thought to be ideal.

It’s worth mentioning that while there is less work on the Vitamin D status of athletes, what work exists suggests that many athletes show Vitamin D insufficiency or outright deficiency levels; depending on the study and the definition used this may be as high as 90% of the athletes tested.  This is especially true for athletes involved in indoor sports, or who train in areas with a harsh winter that limits sun exposure (while Vitamin D levels go up during summer training, they are only maintained for perhaps a month or so without supplementation or sun exposure.  Interestingly, even athletes in sunny areas, such as Qatar may be at risk for deficiency, probably due to athletes preferring to train after sundown since it’s about a billion degrees during the day.  It’s only athletes who live in temperate year round sunny climates that are likely to not be at risk for Vitamin D deficiency.

And from that standpoint alone, supplementation is probably warranted for athletes who train indoors or who live in cold weather areas where sun exposure for a great part of the year simply isn’t available (note that the use of a tanning bed would be another option so long as the duration are moderate).

Mind you, the direct data on Vitamin D and athletic performance isn’t major except for what I talked about above, a handful of studies have examined it and there does appear to be a positive correlation between Vitamin D status and things like strength and muscle force, along with decreased risk of stress fracture (important for athletes in high-impact activities).  Mind you, claims such as “The higher the Vitamin D status the better your performance” are absolutely not supported by current research; it’s likely that it’s more an issue of correcting a highly likely deficiency or insufficiency.

In terms of arguments against supplementation, the main one is the overall lack of data indicating a performance boost; mind you that keeping an athlete healthy in general terms (and Vitamin D contributes to immune system function and bone health) is just as critical here.  An injured or sick athlete isn’t training nor performing and the realities of Vitamin D deficiency should be addressed regardless of whether or not it improves performance.

The other argument against has to do with toxicity, as a fat soluble vitamin, it is possible to take too much Vitamin D.  It does take pretty stupid levels but athletes often fall into a ‘more is better’ trap.  But this is more to do with ensuring that athletes don’t do stupid things and take 5X the recommended dose than the supplement itself.  I’d note that roughly 30 minutes of direct sun exposure pretty much maxes out Vitamin D synthesis (at roughly 10,000 IU’s) in the body and this might be taken as a rough realistic maximum daily intake level.  Others have set more conservative maximum intake levels of 4000 IU’s/day; at the current time it’s not really known what level of supplementation is toxic or problematic.

Finally the authors note that there is individual difference in the absorption and utilization of Vitamin D and this could conceivably impact on how a given athlete responds to supplementation (a great deal of research suggested a problem with Vitamin D levels in obesity but that’s a different research review).  The authors recommend that, while there is little evidence that Vitamin D supplementation will improve performance (outside of correcting a deficiency), athletes should monitor their Vitamin D levels and supplement as needed.  Again I’ll give my recommendations below.


My Comments

For the most part what I wrote above doesn’t really differ to any signicant degree from what I wrote in the articles Supplements Part 1 and Supplements Part 2.  In terms of anti-oxidant supplementation, I’m really not a fan under most circumstances.  Not only do they not appear to have much if any benefit, especially taken in isolated form in high-doses, they may actually be detrimental to training adaptations.  Using them during a primary training phase could slow adaptations.  In contrast, athletes in heavy competition might consider supplementation; some studies do show decreased muscle soreness and damage and taking them during a heavy competition schedule might be worthwhile simply to keep the athlete in one piece.  That’s in addition to NAC having a potential ergogenic benefit before certain types of endurance performance.

In terms of Vitamin D, outside of those athletes who can train consistently in the sun, I think supplementation is probably mandatory.  Few athletes live in climates where outdoor sun exposure is available year round and the simple fact is that even if optimal levels occur during summer training, they only maintain about a month or so after the stimulus of regular sun exposure is removed.

Athletes who’s sports keep them indoors, or who live in areas with actual winter (where training is done indoors by choice or there is simply limited sun exposure) will find Vitamin D levels falling rapidly, potentially compromising immune system function, bone health and even trainability.  Supplementation (or going to the tanning bed a few times per week for reasonable amounts of time, perhaps 30 minutes 2-3X/week) will serve to maintain optimal Vitamin D status during those time periods.

And while it would be ideal for athletes to get regular blood work to determine levels along with their response to supplementation it’s not cheap work to do and has to be done at least twice.  For athletes that can get it done, I’d mention that it takes, on average, 100 IU of Vitamin D to raise levels by 1 ng/mL.  So an athlete with a Vitamin D level of 30 ng/mL who wants to get to 50 ng/mL would need 2000 IU’s per day.

As I noted above, 30 minutes of direct sun exposure generates 10,000 IU’s of Vitamin D and that appears to be the maximum the body will synthesize.  A daily intake of half that should be more than safe and is in keeping with other maximum daily recommendations of 4000 IU/day.  And outside of extreme deficiencies, that level should cover most folks (that is if we assume levels drop to an insufficient 20-30 ng/mL during the winter, 5000 IU/day would be expected to raise that to 70-80 ng/mL right in the middle of the optimal range).

I’d note in closing that, as a fat soluble vitamin, Vitamin D should be taken with a fat containing meal for optimal absorption, Vitamin D is also a supplement that can be taken only weekly (i.e. 35,000 IU’s all at once or what they’d get from 5000 IU’s per day for a week) for athletes who are bad about taking pills.

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