Multivitamins And Prostate Cancer
Chester J. Zelasko, Ph.D. | May 29, 2007

Science by press conference has struck again. The headlines read, “Taking too many vitamins may increase men’s risk of dying from prostate cancer.” Needless to say, Better Life has been flooded with phone and e-mail questions about whether this study means men should stop taking their multivitamins and other supplements.

This provides a good opportunity for me to address something that happens a lot in this type of approach to health reporting by the mainstream media: the focus on relative risk versus absolute risk. This Newsletter will help you understand what the researchers really found in the study compared to what was reported by the media.

What was the study about?
The objective was to examine the health habits of retired men; this study compared men who did and did not develop prostate cancer. The U.S. National Institutes of Health (NIH) conducted the study on members of the Association for the Advancement of Retired people (AARP). Data were collected about diet, supplement use, demographics, health-related behaviors, and cancer risk factors via questionnaire between 1995 and 1997. The study included data on 295,344 men. Then these men were tracked for five years. Researchers used cancer registries from eight states to track the number of cases of prostate cancer and prostate-cancer death.

What were the results of the study as reported in the press?
The press release focused on a segment of the study that examined the subjects who used a multivitamin more than seven times per week compared to those who did not use a multivitamin at all. The number of men per 100,000 person-years of follow-up who developed advanced prostate cancer was 143.8 for the supplement users compared to 113.4 for the non-users (1). When looking at the cases of fatal prostate cancer, the number per 100,000 person-years was 18.9 for the supplement users and 11.4 in non-users. (Person-years are the number of people multiplied by the number of years they were observed. It allows researchers to standardize the results when some subjects may have been followed only two years while others were followed for all five years of the study.) The researchers then performed advanced statistical analyses to see if there were specific factors associated with the higher cancer rate. They found that men with a strong family history of prostate cancer as well as those taking additional amounts of selenium, beta-carotene, or zinc were at the highest risk.

What did the data actually reveal?
The real problem with science by press conference is that too often, perspective is lost. The following are five important factors of the study that didn’t make the news:
  • Relative risk versus absolute risk
    In this study, researchers reported the relative risk of developing prostate cancer when taking a multivitamin more than seven days per week, every day in a week, one to six times per week, and never taking a multivitamin. The same approach was used in the studies of hormone-replacement therapy and the increased risk of heart attacks in women several years ago (2). In this study, if a man took no multivitamins at all, 113 out of 100,000 person-years of follow-up developed prostate cancer compared to 144 of those who took a multivitamin more than seven days per week. As stated earlier, this is the relative risk. But let’s calculate the absolute risk. To do that, you take each total per 100,000 and divide by 100,000: 113/100,000 converted to a percentage is 0.11% while 144/100,000 is 0.14%. Either way, it’s less than one-sixth of one percent. The absolute risk is the difference between the two--about 0.03% or one-thirtieth of one percent--whether you take multivitamins excessively or not. Not quite as ominous, is it? The same approach can be used for the increased deaths from prostate cancer.

  • The lack of statistical significance
    Also lost from the press release was that the analysis for the trend of relative risk cited above was not statistically significant. When analyses of results don’t meet statistical significance, that means the differences could have occurred purely by chance and thus don’t mean anything in the real world. For better or worse, that’s the standard by which scientific results are judged by scientists and in journals like the Journal of the National Cancer Institute. It’s like whether you owe $30,000.02 on your car or $30,000.01--doesn’t really make much difference, does it?

  • The rate of prostate cancer
    Also lost was that the rate of prostate cancer in men over 50 is naturally low. Of the more than 295,000 men in the study, only a little over 10,000 men developed prostate cancer over five years. That works out to be about 3.4%. If you look just at the men who took a multivitamin more than seven days per week, the rate is 3.6%. By any standard, the rate of prostate cancer in men over 50 is low. Of course, we would like it to be zero, but just over 3% is low nonetheless.

  • Alternative explanations
    The researchers did give some alternative explanations for their results. I think the one that carries the most weight is that men who take vitamins take better care of themselves. That means they may eat a better diet, exercise, don’t smoke, and most important, go to the doctor for regular check-ups that include prostate exams. What the very small difference in cancer rates in men who used a lot of vitamins versus those who used none might indicate is that their cancer was detected earlier than cancers in the non-vitamin users. Although that might make the number of incidents higher, there’s no question it’s better to know sooner so you can consider your options.

  • Questionnaires
    The data collected from dietary questionnaires are always suspect in my opinion. In this case, the dietary recall asked about the number of servings of different foods over the past year! Can you tell me how many apples or chicken breasts you’ve eaten in the past year? When it comes to multivitamins, they listed three types: a stress tab, a Theragran type, and a one-a-day. A man could have been taking a stress tab that contained only B vitamins along with a one-a-day-type multivitamin. The three types were pooled, and that’s how it could be more than seven days per week. (I’m sure you’ve been wondering that throughout the whole paper.) I hesitate to criticize a study that was such an enormous undertaking, but because of the use of such a questionnaire, the results should show an overwhelming difference before much credence is given to them. That was not the case in this study.

The Bottom Line
The study reported no increase in cases of prostate cancer between those who didn’t use multivitamins versus those who took a multivitamin every day. If you’ve been taking a multivitamin every day, there’s no reason to change that based on this study.

But I think there are questions that this study did raise. What would be the difference between synthetic vitamins versus natural vitamins? What effect might plant concentrates with phytonutrients have if they were included in multivitamins? What about the role in prostate cancer of omega-3 fatty acids--not typically contained in multivitamins?

Based on the current research, I advise taking a high-quality multivitamin that contains plant concentrates along with a high-quality fish-oil omega-3 supplement. No press conference is required for that recommendation.

References:
  1. Lawson KA, 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--64.

  2. Risks and benefits of estrogen plus progestin in healthy postmenopausal women: principal results from the Women's Health Initiative randomized controlled trial. JAMA. 2002. 288(3):321-33.
BBBOnLine Reliability Seal © 2011 Better Life Unlimited™
A division of Better Life Institute © (BLI, Inc.)
 Contact Us  |  Privacy Policy
SecurityMetrics Credit Card Safe