Dietary supplements shown to increase cancer risk

Byers.940

Tim Byers, MD, MPH, shows that taken in excess, dietary supplements can increase cancer risk

While dietary supplements may be advertised to promote health, a forum at the American Association for Cancer Research (AACR) Annual Meeting 2015 by University of Colorado Cancer Center investigator Tim Byers, MD, MPH, describes research showing that over-the-counter supplements may actually increase cancer risk if taken in excess of the recommended daily 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,” explains Byers, associate director for cancer prevention and control at the CU Cancer Center.

The line of research started 20 years ago with the observation that people who ate more fruits and vegetables tended to have less cancer. Researchers including Byers wanted to see if taking extra vitamins and minerals would reduce cancer risk even further.

“When we first tested dietary supplements in animal models we found that the results were promising,” says Byers. “Eventually we were able to move on to the human populations. We studied thousands of patients for ten years who were taking dietary supplements and placebos.”

The results were not what they expected.

“We found that the supplements were actually not beneficial for their health. In fact, some people actually got more cancer while on the vitamins,” explains Byers.

One trial exploring the effects of beta carotene supplements showed that taking more than the recommended dosage increased the risk for developing both lung cancer and heart disease by 20 percent. Folic acid, which was thought to help reduce the number of polyps in a colon, actually increased the number in another trial.

“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.”

Byers says that people can get the daily recommended doses of vitamins and minerals in their diets by eating healthy meal and that many adults who take vitamin supplements may not need them.

“At the end of the day we have discovered that taking extra vitamins and minerals do more harm than good,” says Byers.

Many recent news reports stemming from this news release present incomplete data. The data source for this article is a 2012 review published by Byers et al in the Journal of the National Cancer Institute, linked from the PubMed record here: http://www.ncbi.nlm.nih.gov/pubmed/22534785

About the author: Garth Sundem

In addition to writing for the University of Colorado Cancer Center, Garth is the author of the books The Geeks' Guide to World Domination, Brain Candy, and Geek Logik. Contact him at garth.sundem [at] ucdenver.edu.

6 comments

  1. Laura Macfarlane says:

    Hi Garth,
    Could provide references to the trials you refer to in you article? “One trial exploring the effects of beta carotene supplements showed that taking more than the recommended dosage increased the risk for developing both lung cancer and heart disease by 20 percent. Folic acid, which was thought to help reduce the number of polyps in a colon, actually increased the number in another trial.”

  2. Laura Macfarlane says:

    Hi Garth,
    Is this current blog based on a recent systematic review on dietary supplements and cancer? If so where and when is that review to be published?

    Could you also provide references to the trials you refer to in your article?

    “One trial exploring the effects of beta carotene supplements showed that taking more than the recommended dosage increased the risk for developing both lung cancer and heart disease by 20 percent. Folic acid, which was thought to help reduce the number of polyps in a colon, actually increased the number in another trial.”

  3. I would like to get scientific references that Tim Byers, MD referred to at the American Association for Cancer Research (AACR)

    • Garth Sundem says:

      Hi Louis and Laura,
      Thanks for your notes! Let’s see if I can help with references to the trials mentioned in the Byers article:

      Folic Acid: Cole BF, Baron JA, Sandler RS, et al. Folic acid for the prevention of colorectal adenomas: a randomized clinical trial. JAMA. 2007;297(21): 2351–2359.

      Beta Carotene: Omenn GS, Goodman GE, Thornquist MD, et al. Effects of a combination of beta carotene and vitamin A on lung cancer and cardiovascular disease. N Engl J Med. 1996;334(18):1150–1155.

      Vitamin E: Klein EA, Thompson IM Jr, Tangen CM, et al. Vitamin E and the risk of prostate cancer: the Selenium and Vitamin E Cancer Prevention Trial (SELECT). JAMA. 2011;306(14):1549–1556.

  4. George says:

    Interesting article. Does the same findings observed in supplements carry forward on juicing? I “juice” to supplement foods that I would normally not eat, or not eat enough of – but it is still a form of supplements. Thoughts?

  5. Kelly Redard says:

    I suspect that people that eat badly take more vitamins and that its the food they eat that causes the increased risk of cancer.