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Can Antioxidants Prevent Cancer?

May 03 2009

You will find a lot of people taking multivitamin, Vit C, Beta carotene, & Vit E to prevent cancer.But the recent cancer prevention studies paints an entirely different story.

Why use antioxidants to prevent cancer?

Prevent Oxidative Stress: Antioxidants can neutralize free radicals or oxidative stress which may cause damage to cells and cell processes , and thereby increase the risk of cancer.

Studies: A large number of epidemiological studies have shown that a diet high in fruits, vegetables, and plants can lower risk of cancer. This same was shown in animals studies and cell culture studies that antioxidants can prevent or delay the development of cancer.

What are the major antioxidants used to prevent cancer?

The major antioxidants used in studies to prevent cancer are: Vitamin E, Vitamin C, Beta carotene, & Selenium.

And did antioxidants prevent cancer?

The results of the studies- spanning three decades of research - have been extremely disappointing to say the least.  A few of the recent large trials showed no benefit of antioxidants for cancer prevention.


Other Nutrients: Even other vitamins like folic acid, Vit b6, B12, Calcium, Vitamin D which showed tremendous hope have failed to deliver.

SELECT Study: The biggest blow to cancer prevention was the recently concluded SELECT study (Selenium and Vitamin E Cancer Prevention Trial), which is the largest cancer prevention study . Though very promising, the study failed to show any beneficial effect of selenium and Vitamin E for reducing the risk of prostrate cancers and was terminated early.

Can antioxidants increase the risk of cancer?

Surprisingly, a couple of studies of large studies have shown that antioxidants may increase the risk of cancers.

Increase in Lung Cancer: The CARET study (Beta-Carotene and Retinol Efficacy Trial) showed that beta carotene supplements in smokers increase the risk of lung cancer.  The similar results from the Alpha-Tocopherol, Beta-Carotene Cancer Prevention (ATBC) Study and the high incidence of lung cancer in the participants prompted the researchers to stop the study early.

Increase in Prostrate Cancer: In a recent study (secondary findings), the author concluded that daily supplementation with 1 mg of folic acid was associated with an increased risk of prostate cancer.

Why antioxidant studies failed to prevent cancer?

There has been a lot of explanations. Below are the major ones:

  • The epidemiological studies that showed benefits had whole foods, which usually is a complex mix of several nutrients. The antioxidant studies used specific single nutrient isolated from food.
  • The effects of specific nutrients depend on the genetic make up of the individual.
  • A deficiency of certain antioxidants or nutrient might increase cancer risk. Also an excess of the same nutrient may increase cancer risk. A good example is folate.
  • Oxidative stress & free radicals are not evil. They have a beneficial effect too.


  • The best way to get antioxidants and maybe prevent cancer is eat a lot of fruits & vegetables. The American Cancer Society recommends eating at least 5 servings of these foods every day.
  • We don’t have too much evidence to advocate high doses of single antioxidant to prevent cancer. In some cases, excess may increase the risk of cancer.

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Joe Cannon, MS, CSCS, NSCA-CPT | Wed May 06, 2009  

Finally! Someone besides myself who is talking about the other side of antioxidants that never gets out to the public! As a supplement investigator and the author of a book on dietary supplements I came to the same conclsions as Anoop - get your antiodants from fruits and veggies and leave the high potency antioxidant supplements alone!
Joe Cannon

Anoop | Sat May 09, 2009  

Hi Sara & Joe,

Thanks for the comment.

As I always say, mainstream information is not always right. And people come to conclusions too casually.

And I have nothing against antioxidants. If they show benefits, there is nothing wrong in taking them. But that’s not the case.

Also, the beta carotene study showing harm was in smokers only. So don’t just casually conclude that it should be the case with non smokers too.

Joe Cannon, MS, CSCS, NSCA-CPT | Sat May 09, 2009  

I agree completely. I believe the case for beta carotene is a symptom of a larger issue within the supplement community, i.e., the belief that research on foods translates into the same effect as when nutrients in the food are concentrated into supplements. They dont always mean the same thing. People take lycopene supplement even though the research focused on people who ate tomato and tomato sauce. Folic acid supplements (but not folate in foods) may be linked to higher colon and prostate cancers. Carrots don’t promote lung cancer as beta carotein supplements appear to. In short, there are no quick and easy fixes.

Joe Cannon | Fri June 18, 2010  

Actually new research on folic acid finds that folic acid supplements and foods that have been artificially fortified with folic acid appear to increase the risk of prostate cancer and colon cancer. This doesn’t happen when people eat foods. Remember cancer needs folic acid to grow too.

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