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Antioxidants may not be worth their salt in preventing cancer

The views expressed are those of the author and are not necessarily those of Scientific American.


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antioxidant supplement cancer prevention american association for cancer researchWASHINGTON—To decrease your risk of cancer, don’t count on antioxidant supplements, a panel of researchers said here at the annual meeting of the American Association for Cancer Research. But assessing antioxidants’ role (and that of many other dietary supplements) in preventing disease has been notoriously difficult.

Antioxidants, such as vitamin C, vitamin E, beta carotene, lycopene and selenium, have worked their way into the public imagination—and even the minds of many clinicians—as boosters of overall health with cancer-fighting powers, given their ability to absorb free radicals, which can do damage to genetic material, as well as what’s been shown in the lab.

Studies of these compounds in vitro present "a lot of reason to believe" they would help prevent cancer in vivo, said Alan Kristal, of the Fred Hutchinson Cancer Research Center in Seattle, at the April 19 panel. But human bodies are a lot more complex than isolated growth factors in petri dishes. And humans—even those in clinical trials—often don’t follow the rules. 

"Antioxidants interact not only with each other but also with other environmental factors," Kristal noted. This is problematic because, as he explained, "people who use supplements use lots of supplements, they don’t just use one." So if, as in some previous studies of several compounds, different antioxidants were shown to have a negative or positive impact on cancer risk, it is often the same individuals enumerated in tallies of each compound’s impact, rather than individual groups being isolated and given only one compound.

Even in randomized, blinded clinical trials, many subjects will still take multivitamins or other supplements on their own in case they are in the placebo group, noted both Kristal and Regina Santella, of Columbia University’s Mailman School of Public Health in New York. In one of her trials, subjects in the placebo group were taking their own vitamins because they could tell if they had been given the active or placebo "vitamin" pills just by the smell of the bottle, she said.

And many health-related study designs often have trouble enrolling and retaining people who aren’t already proactively managing their health and diet. "Factors that predict participation are going to predict not getting the disease," Kristal explained. So in a case-control study, in which a group of cancer patients’ antioxidant intake is measured against that of a "control" population, researchers might be comparing two groups who would have very different baseline health levels to begin with.

Some research has shown slight possible protective effects in various subgroups that have higher cancer risks, such as smokers. There is some evidence that vitamin E can help protect men who smoke against prostate cancer (though Kristal said the findings were "by no means convincing"). And small doses of beta carotene have looked moderately protective against lung cancers in ferrets exposed to tobacco smoke. Larger doses of the compound, however, actually appeared to promote growth of latent tumors in the animals, Santella noted. "One of the potential problems is that we’ve been using the wrong dose of these compounds," she said. But the understanding of the actual mechanisms by which these antioxidants are working remains largely unknown.

It might also be that hunches about antioxidants’ protective effects aren’t entirely off base, but that their value is best accessed by eating the whole foods they come from, such as broccoli, spinach and carrots. "Thinking that one component in a mixture is going to be the answer is probably too simplistic," Santella said. In one animal study, rats that were given tomato powder (a natural source of lycopene) were better protected against prostate cancer than those given a higher dose of the compound in isolated supplement form.

But trying to drill down on whole-foods intake in formal studies can be just as challenging as testing supplements. "Measures of dietary intake are worthless," Kristal said. Not only do people have difficulty recalling what they ate, but also a range of other factors, such as preparation and portion size, can make a big difference in the actual content of many of these compounds.

Many consumers, however, remain dedicated to antioxidants and other supplements as a way to fend off cancer. Adults in the U.S. spend upward of $9 billion a year on vitamins, pointed out New York Times health writer Tara Parker-Pope, who noted that she, personally, had been disappointed to learn through her own research what Kristal concluded at the panel discussion: "There’s really no association between antioxidants and cancer risk in the general population."

Image courtesy of iStockphoto/TampaPhoto





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  1. 1. David N'Gog 9:28 am 04/20/2010

    People want to remain in control of their destiny. They don’t want to hear "taking this pill might not help."

    Consumers will continue to buy anti-oxident pills, even if they’re not as good at supplying protection as the whole-foods because they want to believe they are doing something to extend their lives.

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  2. 2. bertrand_ducharme 8:17 pm 04/20/2010

    Some of the comments given by the panel could apply to clinical trials of new prescription drugs . People participating in these trials are often students or people who do it for the money; some are ready to lie about their past medical condition and their use of medical or illegal drugs in order to get the money. It is not always possible to detect them. Many conclusions of these trials are far from being without problems.

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  3. 3. davea0511 11:57 pm 04/20/2010

    This article describes only part of the problem with assessing the value of anti-oxidants and nutritional supplements as a hedge against cancer, furthermore as much as it doesn’t justify the use of nutritional supplements neither does it justify their exclusion. "We haven’t been able to conduct a valid study" does not in any way justify the anti-supplement view promoted in this piece in any way which is nothing short of egregious.

    The bigger problem with past studies of nutritional effectiveness regarding anti-oxidant usage is the consistently poor way in which they are done … for example a recent published finding that Vit C does nothing to ameliorate pregnancy-related hypertension was based on a protocol requiring a mere 1000mg of Vitamin C, which although a magnitude larger than the hotly disputed and absurdly low RDA, is generally considered by experts in the field (namely orthomolecular medicine) at least 1/8th (or less) the amount needed in order to provide any therapeutic effect.

    Of course the rationale for using such relatively moderate doses and then calling them "high" dosages is driven by fear. Big Pharma driven fear: fear of "vitamin toxicity", fear of anything that might be perceived as quackery, fear of repudiation within professional circles. The misleading study I referenced above is a prime example … contrast it with Fred Klenner who did the most astounding studies regarding pregnancy and Vit C using therapeutic levels 60+ years ago and his seminal work has yet to be recognized or attempted to reproduce. Since then biases & fear mongering, documented at the highest levels of the ACS, has reigned supreme using dubious case studies involving guinea pigs and truly dangerous levels of beta carotene with a statistically insignificant sample size to throw doubt on the entire nutritional supplement approach.

    Of course, caution should be exercised regarding fat-soluble supplements and herbals but gee whiz … calling 1000mg of Vit C "large" and dismissing the vitamin as helpful when such a relatively low dose (compared to required therapeutic levels) – borders on malpractice imho.

    Essential oils is another dark horse often ignored and/or wrongfully disparaged.

    Don’t kid yourself. Follow the money. What do you call a cheap and readily available solution to the 2 most costliest illnesses (consuming well over 50% of the revenue in the health industry) if accepted and promoted by the same health industry? It’s called financial suicide. Biases are thus leveraged at every opportunity to control your Doctor.

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  4. 4. ironjustice 8:50 am 04/21/2010

    I notice they do not DISTINGUISH between one antioxidant ‘type’ and another. Iron chelators HAVE been shown to be EFFECTIVE against cancer. The studies are there for anyone to see. One can surmise then the ‘antioxidants’ these researchers found to be of "no use" therefore .. coincidentally .. are NOT the type of antioxidant which ARE iron chelators. I’d hate to think this was anything BUT coincidence though and not a result which was .. orchestrated.

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  5. 5. scotthenderson37 2:42 pm 05/6/2010

    the FDA and Pharmicutical companies have been partners in crime for a long time case in point the FDA back in the 1970′s told us to eat a low salt diet[ sodium being a major neurotransmitter] a couple decades later we have children being diagnosed with bipolar disorder the first drug used to treat this condition was Sodium Lithicate NaLI hmm coincidence? i think not.

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  6. 6. slikvee 5:15 pm 02/12/2011

    What "they" said! While there is no "iron-clad" proof that antioxidants actually alleviate any chance of cancer occurring, are there any really poor prognoses for the taking of large doses of antioxidant containing supplements? Why aren’t people simply encouraged to, rather than spend a fortune of supplements, include high antioxidant rich foods in every meal? It would seem the natural thing to do and certainly not very difficult. I mean, we’ve got to eat every day, right? Most people eat two or three meals a day. Why not included at least one high antioxidant food in each meal? It’s got to do more good than harm!

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