A vast body of epidemiological studies have linked an increased dietary intake of antioxidants from fruits and vegetables to reduced risks of a range of disease, including cancer, cardiovascular disease and diabetes.
However, when such antioxidants have been extracted and put into supplements the results, according to the randomised clinical trials (RCTs), do not always produce the same benefits, and may even be harmful.
This is the conclusion of Dr Lisa Melton from the London-based registered charity, the Novartis Foundation, who wrote the article for the New Scientist. The article is available online and will be included in the weekly print copy to be published August 5, which sells an average of 165 000 copies around the world.
Summaries of the article have also appeared in mainstream publications around the world, including the UK's Daily Mail and Scotsman newspapers.
Increased risk of lung cancer
While the results of some RCTs have been disappointing, the claim that antioxidant supplements "do little or nothing" will undoubtedly be met with dismay by the supplements industry and dedicated consumers alike.
The article in the New Scientist highlights the link between beta-carotene and an apparent increased risk of lung cancer in smokers. “[This result] was a shock,” Dr Barry Halliwell from the National University of Singapore was quoted as saying in the New Scientist article.
"It not only did no good, but had the potential to do harm."
Vitamin E also controversial
Vitamin E has a similar story, said Melton, and noted that only one study – the Cambridge Heart Antioxidant Study (CHAOS) – has reported positive effects of vitamin E for heart health (a 77 percent reduction in heart attack risk).
“Other trials designed to test whether vitamin E supplements could prevent cancers, such as the ATBC study in Finland, also came in negative,” wrote Dr Melton.
In fact, the Alpha-Tocopherol, Beta-Carotene Cancer Prevention (ATBC) study (1998), did report a positive benefit for prostate cancer in smokers who received 50mcg of vitamin E.
An article about disappointing results for vitamin E would not be complete without a mention of the controversial meta-analysis that reported an increased risk of all-cause mortality for people with high vitamin E intake.
Angelo Azzi from Tufts University is however quoted as saying: “[The meta-analysis] is flawed. We re-analysed the data and there is no change in mortality.”
Nutrients pulled out of context
The article also quotes Dr Andrew Shao from the supplement industry trade association, the Council for Responsible Nutrition: “He says that pulling a nutrient out of context and testing it in a clinical trial is not appropriate,” wrote Dr Melton.
It appears however that it was not only the nutrients being used out of context. Dr Shao told NutraIngredients-USA.com that, aside from being quoted out of context, “I never said that testing antioxidants in clinical trials is inappropriate.
"What I said is that the current drug-based (or evidence-based, whichever you prefer) approach used in randomised clinical trials (RCTs) may not be the best approach to assess the health benefits of antioxidants (or other nutrients for that matter), and that researchers need to rethink how to design and execute such trials.”
“Contrary to what this article surmises, I do think more clinical trials are needed for antioxidants, but it is critical that they are designed and conducted to truly test the question(s) of interest, with the results interpreted and communicated appropriately.
“I don't have the answer for exactly how such studies should be designed, but the current approach needs to be revised.”
Antioxidants have benefits
Dr Halliwell is quoted as saying that he does believe that antioxidants do play a part in the health benefits reported from observational studies. Theses studies show that people eating a diet rich in such compounds have lower risks of heart disease, cancer and diabetes.
Halliwell argues that antioxidants in the diet are protected from rapid digestion being bound into the fibrous material of the fruit and vegetables.
“Supplements may not replicate this effect because they are digested too quickly,” reported the article.
Dr Shao offered an alternative explanation concerning the disappointing results from the RCTs that was not mentioned in the New Scientist article. He told NutraIngredients-USA.com that “the majority of large-scale, high-profile RCTs (including those mentioned in this piece) tend to be conducted in diseased populations.”
“However, these trials do not test the question of whether, for example, vitamin E supplementation can reduce the risk of a heart attack in the general healthy population. Instead, they are testing the question of whether vitamin E and statins and beta-blockers and diuretics etc. can reduce the risk of a second heart attack in very sick patients. These are two very different questions, but unfortunately that message is lost when the results and conclusions are communicated to the public,” said Dr Shao.
Dr Melton however said that the main conclusion to be communicated is becoming clear: “Whatever is behind the health benefits of a diet rich in fruits and vegetables, you cannot reproduce it by taking purified extracts or vitamin supplements.” - (Decision News Media, August 2006)
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