The Latest Findings on Supplements and Cancer Risk
If some is good, is more always better? For cancer risk, the question has been asked and tested for numerous compounds found in foods. After all, AICR's expert report and its updates show that eating plant foods high in specific vitamins, minerals and other phytochemicals reduce risk of many cancers.
Recommendations from a panel of experts along with a major study published this month find that for healthy adults, the answer is a clear no for a few supplements, and it’s unclear for the others. At least for healthy adults with no special nutritional needs.
“These new recommendations [from the US Preventive Services Task Force] provide further evidence that vitamin and mineral supplements do not protect healthy adults against cancer.” Said AICR Director of Research Susan Higginbotham, PhD, RD, “Although it’s possible that as evidence continues to accumulate, certain supplements will be found to be helpful for specific populations, for now research indicates there is no benefit from most supplements and some can even be harmful.”
AICR recommends that people do not rely on supplements to prevent cancer but instead, get the healthful compounds from foods.
No Evidence of Benefit
The analysis of the research was conducted by U.S. Preventive Services Task Force (USPSTF), a government-appointed group of experts tasked to give recommendations on issues of public health. The task force investigated whether vitamin, mineral or multivitamin supplements prevented either cancer or cardiovascular disease.
For both diseases, USPSTF made no recommendation on almost all single dose supplements and multivitamins because there was not enough research to weigh the benefit against the harms. The evidence, they find, is inadequate.
The only two vitamin supplements they found with enough research were B-carotene and vitamin E. For these, the task force recommended against taking either supplement for cancer and cardiovascular prevention. B-carotene supplements increase the risk for lung cancer in smokers, who are at increased risk for this cancer, they concluded. And the evidence showed that vitamin E supplements provide no overall protection.
As the paper notes, many expert organizations along with AICR – including the American Heart Association - recommend that healthy people take in their nutrients by eating a variety of foods rather than supplements.
Increased Prostate Cancer Risk
Another study focused on selenium and vitamin E supplements, finding that high-doses of both increases the risk of the advanced form of prostate cancer. The increased risk from each supplement depends upon whether men start out with relatively low or high amounts of selenium in their bodies.
This study builds on the findings from a large trial that was stopped in 2008 called the Selenium and Vitamin E Cancer Prevention Trial (SELECT). SELECT started in 2001 with approximately 35,000 healthy men randomly placed into groups who either took selenium and/or vitamin E or neither supplement. The trial was stopped when it found the supplements did not offer protection and vitamin E may even increase risk of prostate cancer. The men were asked to stop taking the supplements and researchers continued to follow-up on their health.
This study used data from the 1,739 men who were diagnosed with prostate cancer, compared to a a randomly selected subgroup of approximately 3,000 men from the original study, matched by age and other factors.
For men who began the study with a high amount of selenium, taking selenium supplements increased the risk of high-grade prostate cancer by 91 percent. Among men with low selenium at the start, vitamin E supplementation increased their total risk of prostate cancer by 63 percent. It also increased risk of high-grade cancer by 111 percent. There was no increased risk of prostate cancer among men who did not take supplements.
The dose of supplements the men took was relatively high. For selenium, it was 200 mcg/day – about four times the recommended daily intake – vitamin E supplements were 400 IU/day.
There are many reasons a person may need to take supplements. Folic acid suppements are recommended for women who are or may become pregnant, for example. And these studies in general included healthy adults, over age 50 typically.
Yet for many people, food appears to be the best way to take in nutrients because there's just a lot we don't know about how high doses of otherwise healthy compounds affect our body, says Higginbotham. "But we know the compounds in every apple or other plant food act synergistically. Whole foods are powerful.”
Sources: Virginia A. Moyer, MD, MPH, on behalf of the U.S. Preventive Services Task Force. "Vitamin, Mineral, and Multivitamin Supplements for the Primary Prevention of Cardiovascular Disease and Cancer: U.S. Preventive Services Task Force Recommendation Statement." Ann Intern Med. Published online 25 February 2014.
V.A. Moyer, on behalf of the U.S. Preventive Services Task Force. "Vitamin, Mineral, and Multivitamin Supplements to Prevent Cardiovascular Disease and Cancer: Recommendations From the U.S. Preventive Services Task Force. Summaries for Patients." Ann Intern Med. Published online 25 February 2014.
Alan R. Kristal et al. "Baseline Selenium Status and Effects of Selenium and Vitamin E Supplementation on Prostate Cancer Risk." JNCI J Natl Cancer Inst (2014). First published online: February 22, 2014.