Supplements Lowering Cancer Risk: Insufficient Evidence & Guidelines

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If AICR Blog readers represent the US population, almost half of you will reach for a nutritional supplement at some point today. But if you’re taking that supplement to reduce cancer risk, be aware the evidence just doesn’t support that link. And you should have more guidance from government regulators telling you that, argues a commentary published yesterday in the Journal of the National Cancer Institute.

In the commentary, the authors reviewed the evidence linking cancer risk to several popular supplements, including vitamin D, beta-carotene and folic acid.

As the authors point out, AICR is among an impressive list of health organization who have reached the same conclusion: there is not yet enough evidence to say that nutritional or phytochemical supplements prevent against cancer.

You can read the abstract of the commentary here.

But marketing by the dietary supplement industry is not well regulated, the authors say, and many in the public believe supplements may prevent cancer or are simply harmless. Both scientists and government officials need to do a better job informing the public about the evidence.

It all began, the authors note, with observations in the early 1980s linking diets high in fruits and vegetables to lower risk of some cancers. That led to isolating the compounds and that led to supplement studies.

Evidence from animal studies and observational studies suggested that supplements may lower cancer risk. But further investigations, such as randomized controlled studies (RCTs), have not confirmed these findings. And some RCTs have even shown a supplement may increase cancer risk. For example, a large trial investigating selenium, vitamin E, and prostate cancer risk – called SELECT — was stopped in 2008 due to a link with vitamin E supplements increasing risk of prostate cancer.

The commentary points out that research on supplements and cancer risk needs more study, and the studies are challenging. For example, participants in cancer prevention trials often are health conscious and may already have high levels of the particular nutrient or mineral. It’s possible that if people with low or deficient levels of the nutrient took the supplement they may see a risk reduction; those who already have high levels may increase their risk. A particular nutrient may also link to protecting one part of the body and causing harm to another.

While the research is continuing in supplements, there are evidence-based steps you can take to reduce cancer risk. Diets high in these nutrients and phytochemicals – plant based diets high in fruits vegetables and whole grain – lower the risk of many cancers. And eating a plant-based diet also will help you get to or stay a healthy weight, which also lowers the risk for seven types of cancer.

Here are the basics of what the evidence has shown on reducing cancer risk.


Author: Mya Nelson

Mya R. Nelson is at American Institute for Cancer Research, where she writes about the research in the field.

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