The prostate cancer trials: SELECT, PHSII

Industry reacts to selenium, vitamin trials

By Stephen Daniells

- Last updated on GMT

Related tags: Prostate cancer, Nutrition

Two high-profile clinical trials have reported that selenium and the vitamins C and E are ineffective against prostate cancer. But questions are being asked over the study design.

According to the reaction, the trials do not shut the door on the micronutrients in cancer prevention. Indeed, the reaction asks more questions about the role of nutrition in the maintenance of health and prevention of chronic diseases.

To read NutraIngredients’ report on the study findings, please click here​.

Both studies were published online ahead of the January 7th, 2009 issue of the Journal of the American Medical Association​. In an accompanying editorial, Peter Gann, MD, ScD, from the University of Illinois at Chicago, said the results were "disappointing news".​[1]

Putting the issues in the context of the bigger picture of how studies are performed, Gann said: "...single-agent interventions, even in combinations, may be an ineffective approach to primary prevention in average-risk populations.

“It may be time to give up the idea that the protective influence of diet on prostate cancer risk...can be emulated by isolated dietary molecules given alone or in combination to middle-aged and older men. ...

“On the other hand, non-pharmacological dietary prevention of prostate cancer is probably more complex and may involve certain inconvenient truths. Fortunately, no dietary change this profound is likely to be beneficial for prostate cancer alone.

“If it requires whole foods, extracts, or dietary patterns, it may be necessary to give up the reductionist need to know which molecule is most responsible and perhaps give up the notion of placebo controls as well."

"Epidemiology teaches that every statistical association has only 3 possible explanations: bias, chance, and cause. Regarding nutritional prevention of prostate cancer, first-generation phase 3 trials were too reliant on biased interpretation of prior research, second-generation trials may have been too reliant on chance, yet there is every reason to believe that the next generation will have a firmer basis for causal hypotheses."

There is no ‘I’ in team

Dr Pamela Mason, scientific advisor to the Health Supplements Information Service (HSIS) added that nutrients should not be viewed independently.

“[Vitamins and trace elements] are intended for health maintenance and for making up dietary gaps in the population. Every single officially recognised vitamin, mineral and trace element - not just two or three of them - is required to maintain health,”​ she said.

“Such studies as these two are often conducted to look at potential biochemical mechanisms for individual molecules and do not address health maintenance. All three nutrients – selenium, vitamin E and vitamin C are essential for health,”​ said Dr Mason.

“Vitamins and trace elements are not intended to be used like drugs,”​ she said.

The over simplification of nutrition

These views were echoed by Andrew Shao, PhD, vice president, scientific and regulatory affairs for the trade association the Council for Responsible Nutrition (CRN). Dr Shao said that one reason for the explaining the “apparent conflict”​ between the new studies and previous studies that found positive effects could be due to effects of nutrients in the human body being complex and influenced by many variables.

“Understanding the causality of chronic disease is equally complex. Randomised clinical trials (RCTs) may be inherently limited in their capacity to address the unique challenges presented by nutrients and dietary interventions. Nutrients appear to work best in combination with other nutrients, yet RCTs tend to examine effects of unique chemical molecules in isolation - which is how pharmaceuticals work.

“Further, in using RCTs to study nutrition questions, there is the challenge of being able to create a true control or placebo group. For example, in contrast to pharmaceuticals, it is both impossible and unethical to ensure participants in the control group are not exposed at any level to vitamins and minerals,” ​he said.

“Perhaps we need to revise our expectations that one single healthy habit will serve as a ‘magic bullet’,”​ added Dr Shao.

They just don’t work

Dr Jodie Moffat, health information officer at British charity Cancer Research UK said the SELECT and PHSII studies mean it “is even less likely than we previously thought that supplements can protect against prostate cancer”​.

“There are a lot of studies looking at whether vitamin and mineral supplements can reduce the risk of cancer but many of them, like this one, don’t support a link,”​ she said.

Sources: [1] Journal of the American Medical Association​2009, Volume 301, Issue 1, doi:10.1001/jama.2008.863“Randomized Trials of Antioxidant Supplementation for Cancer Prevention: First Bias, Now Chance: Next, Cause”​Author: P.H. Gann

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