In brief the authors investigated the association between multivitamin use and the risk of prostate cancer (localized, advanced, and fatal) in a group of 295344 men enrolled in the National Institutes of Health (NIH)-AARP Diet and Health Study.

The subjects were cancer free at enrollment in 1995 and 1996.

During 5 years of follow-up, 10241 participants were diagnosed with incident prostate cancer, including 8765 localized and 1476 advanced cancers.

In a separate mortality analysis with 6 years of follow-up, 179 cases of fatal prostate cancer were ascertained. Multivitamin use was assessed at baseline as part of a self-administered, mailed food-frequency questionnaire.

Based on that information the conclusion was reached that multivitamins have no preventative effects against prostate cancer and in fact could promote the development of aggressive forms of the disease.

Some of our readers will now wonder if they should stop taking vitamins altogether.

The Longevity Institute has analyzed this paper and found that most of the claims by its authors are poorly supported, or can be interpreted differently.

First it should be noted that information garnered by questionnaire has limitations and even the authors themselves admit that differences between the users of multivitamins and nonusers could not be assessed and may obscure the true relationship between multivitamin use and prostate
cancer.

Other limitation of the study admitted by the authors include: Small case numbers, absence of information concerning family history of prostate cancer, absence of information regarding duration of multivitamin use which may have helped to determine whether associations were limited to long-time users.

Residual confounding due to history of PSA and digital rectal examination screening may exist as this information was not available for all participants at baseline.

Because of these uncertainties, it is not surprising that regular multivitamin use was found not to be associated with the risk of early or localized prostate cancer. However that taking high levels of supplements increases prostate cancer risk does not necessarily follow from their study.

An alternative explanation of their results is that men who are aware of being at higher than average risk of prostate cancer are likely to consume larger amounts of vitamins and trace elements in an effort to reduce their risk of developing the disease.
The authors of the article actually state this much themselves:

(Quote) "The increased risk of advanced prostate cancer and prostate cancer mortality with heavy use of multivitamins among men with a positive family history of prostate cancer could be due to men with a positive family history taking additional, unspecified supplements as part of a 'prostate health' package to prevent the future development of prostate cancer...

Thus, confounding associations between individual agents that we were unable to assess and the risk of prostate cancer among men with a positive family history in our study were possible." (End quote)

Millions of Americans have been taking multivitamin- and mineral supplements as a general health maintenance measure for decades, and more recently, to reduced the cancer risk. If this had any negative effects it should have resulted in an increase of all cancer, but this did not occur.

The prostate cancer deaths, in fact, declined. by 17 % since 1994! This decline has been attributed to better diagnostic procedures, early detection and improved therapy. However, it could also be because more American men are taking supplemental selenium, an element which has been shown in a placebo-controlled study to reduce prostate cancer incidence by 63%.

One conclusion reached by the authors, however, may be justified; It concerns zinc.

They report that men taking a zinc supplement with multivitamin use at more than seven versus seven or fewer times per week exhibited an increased risk of fatal prostate cancer (RR = 4.36, 95% CI = 1.83 to 10.39), whereas no association with multivitamins was observed for men not taking a zinc supplement (RR = 1.13, 95%CI = 0.46 to 2.80; P value for test of interaction = .042).

This effect may be real because zinc is needed for tumor growth and acts as a selenium antagonist. But this is not a new observation -it was demonstrated by Schrauzer and coworkers 30 years ago.