The association challenges recent findings published in the Journal of the National Cancer Institute regarding an association between multivitamin use and increased risk of prostate cancer.

In comments from Daniel Fabricant, Ph.D., vice president of scientific and regulatory affairs, the Natural Products Association today challenged findings to be published in the May 16, 2007 issue of the Journal of the National Cancer Institute regarding an association between multivitamin use and increased risk of prostate cancer.

“There are a number of reasons why we’re questioning the conclusions of this study. To begin with, this is a cohort study, which is not as reliable as the ‘gold standard,’ a randomized controlled trial. So let's first have some good data in this area before jumping to conclusions. The very nature of statistics is that any researcher with many outcome measures, as was the case in this study, will stumble upon a figure that suggests some kind of an effect where there is none, provided that numerous ways of checking the data are used, as again was the case in this study. As with many cohort studies, there are a large number of variables involved. These missing observations are filled in by the authors’ evaluation of the numbers and then the resulting bias, of which there is a great deal in this study. This is why the best studies ask one research question at a time with one clear cut outcome being measured. This is a large study that was originally intended to improve our general understanding of the relationship between diet and health. It wasn't designed to speculate on the potential for risk.

“Secondly, differences in screening practices may have also had a substantial influence on prostate cancer incidence, by permitting prostate cancer to be diagnosed in some patients before symptoms develop or before abnormalities on physical examination are detectable. Although there is no discussion of this as a variable in the study, on the National Cancer Institute’s own Web site it acknowledges the impact screening practices have in detecting prostate cancer: ‘The evidence is insufficient to determine whether screening for prostate cancer with prostate-specific antigen (PSA) or digital rectal exam (DRE) reduces mortality from prostate cancer. Screening tests are able to detect prostate cancer at an early stage, but it is not clear whether this earlier detection and consequent earlier treatment leads to any change in the natural history and outcome of the disease.’

“Lastly, considering what a strong factor family risk is for all cancers, prostate cancer may also increase in men who have a family history of breast cancer. Other potential risk factors of this nature were not accounted for in the study.”