Study: Taking Too Many Vitamins Increases Cancer Risk

Millions of Americans take vitamins and supplements because they think it will make them healthier. But according to a large-scale study that was just presented at a forum at the University of Colorado Cancer Center, taking too many vitamins increases cancer risk.

Study co-author Tim Byers, MD, MPH explained his research at the American Association for Cancer Research's Annual Meeting at the university. He presented evidence that over-the-counter supplements increase cancer risk if taken in excess.

"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," Byers said in a statement released by the center.

Dietary Supplements and Cancer Prevention: Balancing Potential Benefits Against Proven Harms

The original paper, published in the Journal of the American Cancer Institute in May of 2012, was a meta-analysis of 20 years of published studies on supplements and over-the-counter vitamins.

The research team wanted to investigate the potential health benefits of vitamins and minerals after observing that people who ate more fruits and vegetables had lower rates of cancer. This observation prompted them to investigate if taking supplements and vitamins yielded the same effect. Instead, the scientists found that instead of improving health, taking too many supplements increased the risk of cancer and other fatal diseases.

Byers says in a statement, “We found that the supplements were actually not beneficial for their health. In fact, some people actually got more cancer while on the vitamins." The study authors warned against exceeding the recommended daily amount of vitamin E tablets, beta-carotene, and folic acid. Byers also stated that "there is no substitute for good, nutritional food.”

The Disconnect Between Scientific Evidence and Public Perception

The study also talked about the need for regulation in the supplement industry as a public health issue:

"There is now evidence that high doses of some supplements increase cancer risk. Despite this evidence, marketing claims by the supplement industry continue to imply anticancer benefits. Insufficient government regulation of the marketing of dietary supplement products may continue to result in unsound advice to consumers. Both the scientific community and government regulators need to provide clear guidance to the public about the use of dietary supplements to lower cancer risk."

Is It Safe to Take Vitamins and Supplements?

Matthew Lederman, MD, medical advisor to Forks Over Knives, gave his expert advice on whether people need to take supplements at all. Dr. Lederman's position is that multivitamins will not benefit most people:

"The average person shouldn't just take a multivitamin thinking that it will enhance their health. There is no proof that multivitamins have any benefit for most people, and there is scientific proof that they may cause harm. For example, vitamin A, beta-carotene, folic acid, iron, selenium, and vitamin E are all healthy when you eat them in food, but they have been shown to be dangerous when consumed in supplements. Instead of listening to the marketing claims by the supplement industry, focus on eating whole plant foods to get the essential vitamins and nutrients you need.

Sometimes I might prescribe a specific supplement for an issue that is not responding to diet and lifestyle changes, but I don't recommend multivitamins. I do recommend a B12 vitamin for people on a plant-based diet. "

Martinez, Maria Elena, Elizabeth T. Jacobs, John A. Baron, James R. Marshall, and Tim Byers. "Dietary Supplements and Cancer Prevention: Balancing Potential Benefits Against Proven Harms." Journal of the National Cancer Institute (2012): 732-39. 25 Apr. 2012. Web. 22 Apr. 2015.

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About the Author

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About the Author

Naomi Imatome-Yun

Naomi Imatome-Yun is the editor in chief for Blue Zones and the former managing editor of Forks Over Knives. She has been a food, health, and wellness editor for over 15 years, and her work appears in USA Today, Dining Out, and Art Culinaire. She is a Wall Street Journal bestselling author and was a food expert for for eight years. Find her on Twitter.
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