By Marji McCullough, ScD, RD
Editor's note: Dr. McCullough added the following statement 12/20/13 in response to new studies being released:
Recent findings on multivitamin supplements published after the posting of this blog deserve mention. In 2012, the results of a randomized controlled trial (RCT) of a daily multivitamin supplement were published, showing a small but statistically significant lower risk of all cancers combined in male physicians followed over 11 years. The supplement included 30 nutrients at levels similar to that found in a regular diet in the United States (≤100% recommended daily allowance (RDA)). The U.S. Preventive Services Task Force (USPSTF) recently updated their review of vitamin and mineral supplements for the primary prevention of cancer and cardiovascular disease (CVD) and found there isn't much evidence that multivitamins or supplements help prevent cancer or CVD. But they add that a small benefit from multivitamin supplements on cancer in men was found, based on this study and an earlier RCT in France. The study in France found lower rates of cancer in men, but not women. The authors speculate that this may have been due to worse nutritional status - a generally less nutritious diet in the men - but more research is needed. In the study with the male physicians mentioned above, they all were well nourished but still saw some benefit.
There are still questions to answer about multivitamins and cancer from the RCTs: why only in men? Does whether you have a nutritious diet matter, and to what degree? Are these findings able to be replicated? Longer follow-up from these trials (to see long term effects) may provide more clues. In the meantime, these studies show that lower-dose multivitamins (with ≤100% RDA) appear safe and don't raise risk of cancer or CVD. Still, the best way to get nutrients is through a healthy diet, and the cost of multivitamins can add up. People should discuss the pros and cons of supplement use with their health care professional.
Original blog, 8/16/2011
Can popping vitamin pills prevent cancer? The simple answer is no, based on what we know so far. In fact, some vitamin supplements have even shown harm. What I'm talking about mostly are pills containing individual nutrients in amounts that are greater than that found in food. Before you stop reading, thinking this is simply another "just eat your vegetables" message, let me give you a little history.
Toward the end of the last century, scientists observed that people with healthy diets, and with higher levels of certain phytochemicals ("phyto" for plant) in their bloodstream, such as beta-carotene, had lower rates of cancer. But observations don't prove cause and effect.
So, after careful evaluation of promising dietary compounds, the scientists began planning randomized, placebo controlled clinical trials ("RCTs") with tens of thousands of healthy people to see if taking supplements of individual phytochemicals could actually prevent cancer. RCTs are considered by most to be the gold standard for proving something works. Most of the supplements tested were antioxidants, which are chemical compounds that combat "free radicals" in the body that can damage DNA and possibly lead to cancer. More...