Stop the Presses

Antioxidant Supplements: Helpful or Harmful?

Many people are interested in dietary supplements and their potential to enhance physical performance or promote health. Recently, antioxidant supplements have become popular among athletes and non-athletes alike. In a 2011 article published in the Journal of Sports Sciences, Powell et al. (1) reviewed the evidence for antioxidant supplements in athletes. Not surprisingly, as is also the case with the general population, they found that supplements are not beneficial and may even be harmful.

Whether you are a high performance athlete or a mere mortal interested in the facts on antioxidant supplements, read on…

Antioxidants are compounds that protect cells against the harmful effects of free radicals – chemically unstable molecules that attack the cell’s DNA, membranes, etc. The concern with free radicals generates from their proposed connection to a whole host of chronic diseases. For example:

  • Free radicals attack a cell’s DNA. This damaged DNA may alter cell function and promote cancer development.
  • Free radicals oxidize the “bad” LDL cholesterol. This oxidized form is much more likely to deposit on the walls of the arteries and cause them to stiffen and narrow, affecting blood flow and increasing the risk of cardiovascular disease.

While often only associated with exposure to sunlight (radiation) or chemical toxins (pollution, pesticides, etc.), free radicals are also produced in the body when it undergoes normal metabolic reactions required for survival (breathing, eating) and physical activity. 

Antioxidants neutralize free radicals and stabilize them, thus, preventing them from attacking the cells. Once an antioxidant neutralizes a free radical, however, it is chemically altered and cannot neutralize another free radical. As antioxidants are constantly being used, it is important for the body to have a continuous supply. Fortunately, the body naturally produces antioxidants and can extract them from the foods that you eat.

Fruits and vegetables contain vitamins, minerals and phytochemicals (plant-based biologically active compounds), all of which can act as antioxidants. Vitamin C, vitamin E, selenium and manganese are known vitamins and minerals with antioxidant properties. Phytochemicals number in the thousands, and many have antioxidant properties – green tea, blueberries, pomegranates, dark chocolate and red wine are just some popular foods touted for their antioxidants.

The physiological functions of antioxidants would seem to suggest that high intakes would promote health but what’s the evidence? Powers et al. (1) reviewed the literature surrounding free radical production and antioxidant supplementation in athletes. There is sound scientific evidence indicating that physical activity increases free radical production in the muscles and that athletes have higher levels of free radicals, which can contribute to muscle fatigue in longer workouts. However, a well trained athlete will also produce more antioxidants in response to exercise.

There is a paucity of evidence to suggest that common antioxidant supplements improve performance. In fact, the research to date suggests that antioxidant supplementation has a negative effect on physical performance. The hypothesis is that antioxidant supplementation may actually decrease the natural training adaptation which signals the muscles to produce more antioxidants in response to increased duration of exercise.

Although counterintuitive, evidence suggesting that antioxidant supplements may do more harm than good has also been reported in other populations. A diet high in antioxidant fruits and vegetables decreases the risk of many chronic diseases, however, the overwhelming majority of the studies do not find that taking a single antioxidant supplement, like vitamin E or vitamin C, has any benefits to health. Alarmingly, in the case of beta carotene supplementation in smokers, the majority of the trials found an increase in lung cancer and had to be prematurely terminated (2).

There are many explanations for the differing effects with antioxidant supplements and whole foods:

  • Whole foods provide a variety of phytochemicals, as well as protein, essential fatty acids, carbohydrates, vitamins, minerals, fibre and water; whereas a pill will only provide one or limited number of vitamins/phytochemicals.
  • The full range of phytochemicals available in foods remains unknown.
  • The quantities of phytochemicals found in foods remains to be determined (and therefore the dose to prescribe with a supplement is unclear). It is also possible the phytochemicals need to be taken with other phytochemicals or nutrients to be effective because of synergistic associations.
  • Not all antioxidants are the same, thus, don’t have the same benefits for the body.

No Baloney’s advice. We recommend that everyone, athletes included, avoid antioxidant supplements. Focus on consuming a balanced diet with plenty of plant-based foods rich in antioxidants and other phytochemicals for optimal health and performance. You’ll also get scores of other nutrients, save money and enjoy a delicious meal!


  1. Powers, S. Nelson, WB, Larson-Meyer, E. (2011) Antioxidant and Vitamin D supplements for athletes: Sense or nonsense? Journal of Sports Sciences 29 (S1), S47-S55.
  2. Goralczyk R. (2009) Beta-carotene and lung cancer in smokers: review of hypotheses and status of research. Nutr Cancer. 2009;61(6):767-74

7 thoughts on “Antioxidant Supplements: Helpful or Harmful?

  1. @ japarnell: after taking nutrition classes at MRU and learning important lessons about nutrition especially the subject above about antioxidants, i completely agree with what the author have stated. i agree that people need to have antioxidants in the body to fight free radicals since we are already producing it and we already take it from the foods that we ingest, taking antioxidant pills in the form of supplements does make any sense. there is a saying that “too much is not good for you as much as less is not good for you either”, having too much of some vitamins and minerals or whatever will only harm ones body and instead of helping the body do its job, it just contributes to the harm. and besides even though the people conducting some experiments found out that eating this fruit or vegetable will help decrease the risk of developing this kind of disease, it is still not clear which of the thousands of vitamins, minerals, phytochemicals contributed to it and therefore jumping to conclusion of saying taking so and so as a supplement will decrease the risk of a certain disease is not productive at all. and i just hope that people including myself will continue or even start eating healthy and making healthy choices so that we can live longer. i mean during the time of our ancestors there was no fast food, everything was fresh and cooked at home and they live a longer and healthier life compared to what is happening to our generation today. it is a sad reality that we must all grasp so that we can change our choices and live a healthy life

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