Antioxidants and Cancer – Help or Harm?

Do antioxidants decrease or increase our cancer risk? An examination of the current available information.

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Aug 02, 2017
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Antioxidants and Cancer – Help or Harm?

        Popular culture seems to be full of messaging about how anti-oxidants are these wonderful elixirs that will make us healthier, age slower, and may even prevent cancer! Indeed, a visit to any pharmacy or health food store will reveal a wide array of antioxidant supplements that make dubious and somewhat fanciful claims of health benefits.  So, do anti-oxidants actually help prevent cancer? The reality, is (as always!) a bit more complicated.

       A plethora of studies have focused on many kinds of anti-oxidants, and their effects on several different kinds of cancer. Indeed, a recent search for clinical trials looking at anti-oxidants and cancer, revealed no less than 449 studies. Several large scale studies have attempted to evaluate the benefits of antioxidants for cancer prevention (please see the Table below, for a summary of some of these trials). Specific antioxidants that have been assessed include beta-carotene (a precursor to vitamin A, also what makes carrots orange), alpha-tocopherol (vitamin E), Retinol (vitamin A) and vitamin C. So far, based on these large trials, there was no significant benefit for cancer prevention, and in two trials where there was actual harm, resulting in their early termination. The first study, from the Fred Hutchinson Cancer Center, found that taking vitamin E supplements, doubled the risk of prostate cancer (SELECT trial), and was terminated early. The second study, in which participants were given carotene and retinol supplements (CARET trial), resulted in an elevated risk of lung cancer, and was also terminated early. Thus, the overall picture regarding the antioxidant supplements for cancer suggests that there is no clear benefit, as well as some evidence of actual harm.

         Factors that could be playing a role in the overall disappointing results could be that the antioxidants were consumed as purified chemicals, instead of as food, which is a much more complex mixture. Complex interactions between antioxidant supplements and food components could potentially affect outcomes. The nutritional status of the participants could also be a complicating factor. For example, if a participant is deficient in a particular antioxidant, an initial overall health benefit would likely be observed initially, including potentially cancer outcomes. Whether this initial beneficial result would continue after the antioxidant deficiency is corrected however, remains unclear. Further studies are needed to address these complex and knotty issues. There is some preliminary evidence that antioxidant supplements may be beneficial to some patients in the early stages of certain cancers, however these results remain controversial and need to be more thoroughly assessed.

       So, what is one to do? As of now, the best approach seems to be to try and get antioxidants from our diet, rather than from supplements. This means eating lots of fruits and vegetables which is probably good for our overall health anyway. Other general cancer prevention strategies include maintaining a healthy weight and of course, exercise.

 

Table – Large scale trials evaluating the role of antioxidant supplements for cancer prevention (Source of information: Antioxidant fact sheet from the National Cancer Institute (NCI), available at: https://www.cancer.gov/about-c... )

 

 

Name of Trial

Supplements provided

Results

1

Linxian General Population Nutrition Intervention Trial (China)

beta-carotene, alpha-tocopherol, selenium

Initially promising but no significant overall benefit

2

Alpha-Tocopherol/Beta-Carotene Cancer Prevention Study (ATBC) (USA)

alpha-tocopherol, beta-carotene

No significant effect

3

Carotene and Retinol Efficacy Trial (CARET) (USA)

beta-carotene, retinol

Initial increased risk for lung cancer, no significant effect for prostate cancer. Terminated early.

4

Physican’s  Health Study (PHS I) (USA)

beta-carotene

No significant effect

5

Women’s Health Study (WHS) (USA)

beta-carotene, vitamin E, aspirin

No signficant benefit or harm

6

Supplémentation en Vitamines et Minéraux Antioxydants (SU.VI.MAX) (France)

vitamin C, vitamin E, beta-carotene, selenium, zinc

Different initial results for men and women but no significant overall benefit

7

Alpha-Tocopherol Heart Outcomes Prevention Evaluation–The Ongoing Outcomes (HOPE–TOO) (USA)

alpha-tocopherol

No significant effect

8

Selenium and Vitamin E Cancer Prevention Trial (SELECT) (USA)

Selenium, vitamin E

Increased risk of prostate cancer. Terminated early

9

Physican’s  Health Study II (PHS II) (USA)

vitamin E, vitamin C

No significant effect

 

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Go to the profile of Tia Rai

Tia Rai

Research Assistant Professor - Scientific Writing, The Hormel Institute, University of Minnesota

PhD

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