Antioxidant Supplements May Block Some Benefits of Exercise

by | May 13, 2009
Romanesco Broccoli In A Beaker

Romanesco Broccoli in a Beaker

One of the most consistent themes of nutrition science is that vitamin supplements (pills, powders, liquids, etc.) are almost never able to mimic the beneficial effects of foods that contain the same vitamins. Now new evidence suggests that high doses of these antioxidant supplements–but not whole foods containing them–may actually block the beneficial effects of exercise on insulin sensitivity and metabolism.

Exercise has countless benefits for people of all levels of fitness. One of the most important of these is its ability to improve insulin sensitivity and increase metabolism. For this reason, exercise is considered among the most effective ways to protect against type 2 diabetes.

One of the byproducts of exercise, however, is the production of free radicals that results from the breakdown of oxygen in the muscles. These reactive oxygen molecules can damage cells and DNA, and are implicated in many chronic diseases. Since antioxidants can easily neutralize these reactive oxygen molecules, it has been assumed that antioxidants such as vitamins C and E could only benefit the body.

A new study published in the Proceedings of the National Academy of Sciences suggests that rather than help protect against oxidative damage from exercise, high doses of antioxidant supplements may actually hinder the body’s natural protection against oxidative damage and block exercise-induced metabolic benefits.

In the study, human subjects were given either placebo or 500 mg vitamin C twice per day and 400 IU vitamin E. They were then trained in both cardio and strength training workouts at the gym for 5 consecutive weekdays, 4 weeks in a row. This trial was performed on both previously trained and untrained individuals.

Metabolic rates were tested by blood sample both before the trial and after 1 and 4 weeks of training. Muscle biopsies were taken both before and after the trial for all participants. Several measures of metabolism and insulin sensitivity were measured including plasma glucose concentrations, plasma insulin concentrations, maximal oxygen uptake (VO2 max), as well as several molecular markers in muscle that are linked to insulin sensitivity and are known to promote the body’s natural defense against oxidative damage.

The researchers found that exercise improved measures of insulin sensitivity in all individuals except those given antioxidant supplements. Also, molecules that protect against oxidative damage are upregulated in response to training, but not when antioxidants are administered.

Previous studies suggest that the body’s natural defenses against oxidative damage require activation by a small amount of reactive oxygen chemicals in the body. These same chemicals have been shown to mediate insulin sensitivity in muscles, and in this study both were shown to be blocked by high antioxidant administration.

The researchers suggest that small doses of reactive oxygen molecules such as the amounts produced by exercise are necessary to induce the body’s natural defense against oxidative damage, and that this process is essential for mediating exercise-induced insulin sensitivity. If this is true it could mean that some (but not all) of the metabolic benefits of exercise could be limited by taking high doses of vitamin supplements. This may be particularly important to individuals at high risk for type 2 diabetes.

Interestingly, foods that contain high levels of these antioxidants have previously been shown to be protective against type 2 diabetes. Although the reason for this is still unknown, the authors suggest the benefit is unlikely due to the antioxidant content of the foods and may depend on other factors.

Even if we do not understand the reason vegetables and fruits are the best source of nutrition, we can still enjoy all their benefits. If you choose to continue taking vitamin supplements, it is advisable to stick to a basic multivitamin that does not contain megadoses of one particular nutrient.

Do you take vitamin supplements? Why? How much do you take?

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12 Responses to “Antioxidant Supplements May Block Some Benefits of Exercise”

  1. Sudeep says:

    Hello ,
    Its interesting how the researchers can prove one thing and after few months say it does not .I am sorry but i always question the mind of the lay man .Can you imagine one day antioxidants are good for you , other day it’s bad for you .Cannot we just enjoy food as just food as it is . Cannot we just forget all this antioxidants and stuff . Are we going to eat a hot dog if the scientist modify it and place all the good vitamins , minerals ,and nutrients that is needed .Are we going to eat it ? I am sure no …. then why are we so much sticking to this theory of nutrients which is always changing .This doubts are not raised by me but by this book “In defense of Food” by Mr Pollen …
    No for your question that you raised no i am not taking any vitamins because of this few reasons
    http://www.e-swastya.com/2009/04/5-ways-to-save-on-our-vitamins-bill.html

    Regards
    Sudeep
    Blogging for Optimum Health Care

    • Darya Pino says:

      Thanks Sudeep, I totally agree! To be fair to scientists, however, the data is not always as contradictory as it seems in public. That is more a fault of the media for exaggerating the findings than it is the fault of the scientists for reporting the data. I have no doubt that one day we will be able to explain all the seemingly contradictory advice with perfectly sound science. But for now the data tells us we cannot trust anything but eating fresh, seasonal foods.

      I advocate whole, unprocessed foods for ideal health, and I think it is important to show studies like this that argue against the perceived benefits of supplements.

  2. Ben Lee Handler says:

    As much as I enjoy your blog and the works Michael Pollan, I have to disagree with Sudeep: I would totally eat the Super Hot Dog.

    Are fresh, seasonal foods really the *only* thing we can trust?

    • Darya Pino says:

      Thanks for your comment Ben Lee!

      Personally I eat whatever I want, but I seem to have lost the taste for almost all processed foods because I find them devoid of real flavor and lacking character. I still eat meat, cheeses, breads and desserts and enjoy them thoroughly, but they are always special (aka expensive) versions of these things, otherwise I hardly think it is worth it.

      I don’t know what they put in their hot dogs at Prather Ranch, but I can’t imagine you could stop me from eating them ;)

  3. Karin says:

    Great post Darya!

  4. Claire says:

    I’ve always wondered where fortified foods fit into this. Don’t thoughtfully fortified foods work to correct nutritional deficiencies? Also, were the people in this study deficient in vitamin E and C without the supplements? If they weren’t, this seems to say more about taking in more nutrition than you need, rather than the source. It’s fairly difficult to take in more nutrients than you need with food, but easy to do with vitamins.

    • Darya Pino says:

      Excellent points, Claire. Fortified foods are certainly useful in some situations. One good example of this is the value of folate in pregnancy to prevent neural tube defects.

      Supplements can also be effective sometimes. Vitamin D supplements are helpful against osteoporosis and MS (and maybe cancer) in locations where there is insufficient sunlight.

      Megadoses of vitamins in supplement form do not usually provide additional benefits, though increased nutrition from food can be helpful/protective. The data does seem to suggest that the source of the vitamins is important (food vs. pills or fortified foods) except for in cases of extreme deficiency. For example, the vitamin D in milk has not proven effective against osteoporosis, whereas supplements do seem to be effective. This may be because of the high protein in milk.

      Some scientists hypothesize it is because the vitamins in food work together in specific ratios whereas in pills, vitamins are usually in isolation.

      Honestly I do not think we have enough data to generalize very much, but I lean toward the side of skepticism when I hear about any new vitamin supplement or fortification.

  5. Madison says:

    Hi Darya: I take a multi daily and wanted to know if it is too much to also be taking seperate calcium and vitamin E and C? I cannot tolerate dairy so I take a seperate calcium vitamin to make sure that I am getting enough. I also workout 6 days a week mid to high intensity and I take the vitamin E and C for immunity reasons.

    • Darya Pino says:

      Hi Madison, I do not recommend any of those supplements except the multivitamin. High doses of vitamins C and E have never been shown to provide benefits and in this case they were shown to be bad. As for calcium, you should make an effort to eat plenty of leafy greens and oily fish like sardines. I too cannot tolerate dairy, but do have fortified soymilk in my cereal. I recently had my calcium tested and my level is perfect. But generally too much calcium is dangerous because it is associated with prostate cancer and autoimmune diseases.

  6. Lori Carraway says:

    Hi Darya – wanted to pass on something I noticed since testing out the supplement vs. exercise theory. I was previously taking 2,000 mg of vitamin c every day – 1,000 in the a.m. and 1,000 in the p.m. and working out 7 days a week. After reading this post, I consulted with my nutritionist about my level of vit. C supplementation and scaled it back to 1,000 mg per day. I know, according to this study that is still waaayyy too much! However, after doing that for the past few weeks I have noticed that I am more sore after doing my regular exercise routine (cycle, pilates, running) which I equate to building muscle. Maybe there is something to this?

    • Darya Pino says:

      Wow, that’s really interesting. Thanks for sharing your experience!! This particular study was done in humans (as opposed to rodents) and was pretty well-designed, so I’m not surprised you are noticing a difference. I wonder if better muscle fueling is enabling you to push a little harder and build more? Either way, kudos to you for keeping up your impressive workout routine!!

  7. Marcia says:

    Darya, I so love you for sharing your knowledge and research with us that I want to go back and read all of the blogs you wrote before I found you.

    I have Metabolic Syndrome/Insulin Resistance and was so inspired by your guest blog on MizFit about insulin receptors. I have been eating a very low carb diet for about 6 years, with lots of fruit and veges and protein in the form of chicken, fish and some beef. However, I am still about 20 kilos more than I would like to be. It certainly not easy to live a carb free diet in our culture, though I do eat a fairly ‘clean’ diet.

    I want to begin strengthening exercises and to this end I have purchased a resistance band. In the past, exercise, even walking, has proven difficult for me, as my muscles seem to be fatigued before I begin. When walking, especially up-hill or even with a slight gradient, I develop cramps on the outside of my calf muscles. After reading your blogs, I’m assuming this is because a lot of my insulin receptor’s doors are closed and the energy just cannot get to my muscles when they need it. This, not surprisingly, has led to a reluctance on my part, to exercise.

    My question is: Is there a way I can begin exercising at a level that my body can tolerate, and will not lead to me being discouraged due to muscle fatigue, that I can build on, and finally open all those doors, that I’m sure have been welded closed for a very long time!?

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