Prostate cancer tied to birth-control pills, but why?

(CBS/AP) Are birth control pills to blame for the high rates of prostate cancer? There's no proof, but a provocative new study showed a link between use of the Pill and the number of new cases as well as deaths from prostate cancer.

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Researchers at Princess Margaret Hospital in Toronto compared rates of prostate cancer cases and deaths in 87 countries with rates of contraceptive use - including intrauterine devices, condoms, and vaginal barrier contraceptives. But apart from the Pill, a correlation "was not found among other contraceptive methods," said lead author Dr. David Margel.

Why the connection?

Women on the Pill excrete estrogen in their urine, which gets into the environment - particularly into water. And scientific evidence suggests that low levels of estrogen may cause cancer, including prostate cancer, Margel said.

The researchers used data from the International Agency for Research on Cancer and the UN World Contraceptive Use report to assess both rates of prostate cancer and common methods of contraception.

"What we found was that in countries where the oral contraceptive was used more often, prostate cancer had a greater incidence," Margel said. But he stressed there may be many factors involved, and "this study does not establish cause and effect ... This is a very, very preliminary finding and we're not telling everybody to quit the pill." Confirming the effect of pill-based estrogen alone would take much more research.

While the amount of estrogen excreted by any individual is tiny, "when millions of women are doing it and for a long period of time, it may cause low environmental estrogen levels," Margel said.

Estrogen and estrogen-like chemicals are found in many commercial and cosmetic products, including pesticides. Studies have shown that male farmers exposed to estrogen-containing pesticides have a higher risk of prostate cancer compared with the general population.

Increasingly, compounds known as "endocrine disruptors" are being found in water, according to Fe de Leon, a researcher at the Canadian Environmental Law Association. These chemicals - such as DDT and BPA - are found in everyday objects such as plastic bottles, metal food cans, and detergents.

Society can't ignore the fact that estrogen and estrogen-mimicking substances may have a significant impact during an individual's development and could eventually lead to breast and prostate cancers, DeLeon said. "But it's very hard to make that distinction. It's hard to pinpoint which chemical's responsible for a particular health endpoint. It certainly warrants further investigation."

The study was published in BMJ Open.