A recent paper linking the use of oral contraceptives by women to higher rates of prostate cancer in men has received some media attention. Two urologic oncologists from the University of Toronto in Canada published this hypothesis in an open access journal, BMJ Open. The full text is available here.
The paper’s plausibility is based on some previous work suggesting the exposure to estrogen might increase the risk of prostate cancer.
The study was done using retrospective data from various sources. Information on contraceptive use and prostate cancer was obtained for countries with all levels of economic development on all continents. The main finding was that oral contraceptive use was associated with both the incidence of and mortality from prostate cancer, while all other types of contraception showed no such association.
A fair amount of statistical manipulation was used to generate the results. When one first reads the paper, it is almost believable until one reaches the section postulating the mechanism by which this association could possibly be real. The means by which oral contraceptive use could affect prostate cancer rates is posited as increased levels of so-called endocrine disruptive compounds (in this instance, estrogens) in drinking water secondary to excretion by women.
To their credit, the authors themselves admit that the paper has some serious limitations.
Obviously, more developed countries would have higher rates of cancer screening and detection. Rates of prostate specific antigen (PSA) testing were not available. The authors felt that their method of controlling for gross domestic product obviated the need to have actual PSA screening data.
The authors further concede that there are no available data on the levels of endocrine disruptive compounds in the drinking water of a single country.
As a mere general surgeon with no ecologic or public health credibility but having seen the vast reservoirs of drinking water in my area, I find it difficult to believe that there could be significant levels of endocrine disruptive compounds in the public water supply. And what about the fact that in many highly developed countries, people drink bottled water presumably free of endocrine disruptive compounds?
An [assumed] editorial summary of the paper states “This study is an ecological study and thus has significant limitations with respect to causal inference.” Translation: There is absolutely no proof that oral contraceptive use in women causes higher rates of prostate cancer in men.
Bottom line: I’m not going to stop drinking water. Are you?