Study on Multivitamin Use and Prostate Cancer Risk Creates Confusion and Fear
A study published in the May 16, 2007, Journal of the National Cancer Institute has many people concerned about the use of "multivitamins" and the incidence of prostate cancer. The researchers enrolled 295,344 men in an observational prospective study (as opposed to an interventional study), followed them for 5-6 years, and noted incidence of prostate cancer, incidence of advanced prostate cancer, and death from prostate cancer. They came to the conclusions that men reporting "excessive use of multivitamins (more than seven times per week)" were at a greater risk for developing advanced prostate cancer or dying from prostate cancer. Upon analysis of this study, it sends up a number of red flags that make us doubt the accuracy of its findings.
Red flag #1: In a questionnaire, the men were asked at baseline if, in the past 12 months, they had taken a multivitamin, which was characterized as a "stress-tab type," "therapeutic or theragran-type," or a "one-a-day-type." These "types" of vitamins were not defined, so the box the participant checked on the questionnaire was completely dependent upon their own interpretation of what "type" of multivitamin they had been taking! These multivitamins are typically tablets with numerous non-essential ingredients and contain relatively low amounts of vitamins and minerals. There were no blood tests to assess blood levels of any of the nutrients included in these "multivitamins," so it is impossible to know if any of the nutrients were absorbed. Lastly, this questionnaire was completed only at baseline, so we have no way of knowing if a participant in the study continued taking their supplements, increased the dose, changed products, or discontinued them.
Red flag #2: The researchers' inherent bias is evident in the article, in which they describe ingestion of a "multivitamin" more than seven times in a week to be "excessive."
Red flag #3: Researchers assessed iron, zinc, selenium, and folic acid intake "by asking participants whether or not they had used each of these individual supplements more than once per month in the past 12 months (yes or no)." They did NOT inquire about frequency of use or dose; however, this did not stop them from drawing conclusions about relative risk of localized prostate cancer incidence in "heavy multivitamin users who consumed a selenium, folate, or vitamin E supplement." To be fair, they did ask about vitamin E dosing and they say they did find a statistically significant increased risk in men who took over 800 IU of vitamin E daily along with a multivitamin. They did not find this increased risk in men using vitamin E alone. However, this finding is also questionable because of the points made in "Red Flag #1" above.
Red flag #4: They report increased relative risks for advanced and deadly prostate cancers in "heavy multivitamin" users, compared to "never" users. These relative risks got even larger when they split the group into those who didn't have a family history of prostate cancer and those who had a family history, with the family history group having a greater relative risk. However - and this is probably the most important point - none of these results was statistically significant! There were so few cases that there was no way to get statistical significance. However, they still reported in their abstract and in their press release that men who take a multivitamin are at increased risk! And to double the stupidity level, in an accompanying editorial in the same journal, titled "Surviving Antioxidant Supplements," the authors try to equate this research with other poorly done studies on antioxidants, even going as far as saying the current study adds to the "growing evidence that questions the beneficial value of antioxidant vitamin pills…". This study wasn't about antioxidant vitamins!
Red flag #5: Their conclusions. They concluded that men with a family history of prostate cancer were at greater risk for advanced or fatal prostate cancer if they used a multivitamin. However, those men who know they have an increased risk (because of family history) are precisely the people who would take more nutrients to try to reduce their risk. They also have themselves tested via PSA and/or digital rectal exam more often than men without a family history. They might also be more inclined to increase their daily dosage of vitamins, minerals, and herbs if they had any prostate symptoms. In fact, the authors state, "…the observed relationship between multivitamin use and advanced prostate cancer…may have been due to increased multivitamin use among men with early symptoms related to prostate cancer." Again, we have no way of knowing if indeed these people even took a multivitamin or any other supplemental vitamins or minerals continuously throughout the duration of the study.
It is unfortunate that this kind of research gets "media legs," since the questionnaire used in the study, and thus the data gathered, was so nebulous. The results are meaningless; however, they could be very difficult for the layperson to decipher because of how the article was written and the amount of misinformed media attention it got. Instead of furthering the understanding of true disease risk, studies like this tend to only create confusion and fear.
Lawson KA, Wright ME, Subar A, et al. Multivitamin use and risk of prostate cancer in the National Institutes of Health-AARP Diet and Health Study. J Natl Cancer Inst 2007;99:754-764.
