Further Comments on Prostate Cancer/Vitamin Link

As we suspected, 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.

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.’

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.

The research is at odds with a nested study published recently in The American Journal of Clinical Nutrition that reported an increased selenium intake in combination with a daily multivitamin may reduce the risk of prostate cancer by about 40 per cent.

Most importantly, many multivitamin/minerals contain the daily recommended intake for iron (18 mg.). Men should never take supplemental iron (18 mg. or more) unless iron anemic. Excess stored iron may produce health risks, including the allowance of cancer cells to reproduce more rapidly. This is why we always recommend working with a knowledgeable health professional to look at individudal needs.

As we alluded to in an earlier blog, Dr. Goran Bjelakovic commented on this study in an editorial and was quoted in the press release that appears in this issue of Journal of the National Cancer Institute. He is not directly involved in the study. However, we are still very wary of his involvement in any study supposedly without bias.

To read the abstract (summary of the study), go to http://jnci.oxfordjournals.org/cgi/content/abstract/99/10/754