Take lots of dietary supplements? You may have increased cancer risk, says new meta-study.

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Dr. Tim Byers, who is the director for cancer prevention and control at the University of Colorado Cancer Center, conducted a meta-analysis of 12 trials involving more than 300,000 people, over 12 years -- and found that high doses of certain vitamin supplements were linked to increased odds that a person would develop certain kinds of cancer.

The summary of his paper, released this week: “While dietary supplements may be advertised to promote health, new research shows a link between consumption of over-the-counter supplements and increased cancer risk, if the supplements are taken in excess of the recommended dietary amount.”

"We are not sure why this is happening at the molecular level but evidence shows that people who take more dietary supplements than needed tend to have a higher risk of developing cancer," wrote Byers in the study findings.

"This is not to say that people need to be afraid of taking vitamins and minerals," says Byers. "If taken at the correct dosage, multivitamins can be good for you. But there is no substitute for good, nutritional food."

Dr. Tim Byers.


Dr. Tim Byers.

From a CBS News report:

Byers began his investigation on the association between supplements and cancer risk 20 years ago. He and many other researchers observed that people who ate more fruits and vegetables cut their risk for cancer. Byers and his colleagues wondered if taking supplements that provide the same vitamins and minerals as fruits and vegetables could offer similar protection.

But his findings suggested just the opposite -- rather than warding off cancer, taking lots of supplements may raise a person's risk. Byers presented his research Monday at the annual meeting of the American Association for Cancer Research, in Philadelphia.

Through his analysis, Byers found that people who took high doses beta carotene supplements had an increased risk for lung cancer. Selenium supplements were associated with skin cancer. Men who took vitamin E had an elevated risk for prostate cancer. Folic acid, a B vitamin, taken in excess could lead to an increased risk for colon cancer.

Previous studies on this same topic have shown that taking lots of supplements has no measurable effect on cancer risk:

An analysis of 24 studies and two trials published in the Annals of Internal Medicine in 2013 looked at the role of vitamin supplements for the prevention of chronic diseases. That study involved more than 350,000 people and it found little evidence that vitamin and mineral supplementation impacted the risk for a number of chronic health conditions, including cancer.

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