There is a significant link between use of oral contraceptives or birth control pills and the incidence of prostate cancer, said researchers who set out to investigate the suggestion that byproducts of these drugs get into the environment, for instance the water supply, and lead to an increase in low level estrogen exposure in affected populations.

David Margel, and Neil E Fleshner from the Princess Margaret Hospital at the University of Toronto in Canada, write about their findings in the 14 November online issue of BMJ Open. They conclude that their study shows a significant association between oral contraceptives and prostate cancer and that:

“It is hypothesised that the [oral contraceptive] effect may be mediated through environmental oestrogen levels; this novel concept is worth further investigation.”

Several studies have already suggested that exposure to estrogen may increase the risk of prostate cancer, so Margel and Fleshner took this a stage further: what if use of oral contraceptives could be placing enough estrogen into the environment that it increases prostate cancer risk in the exposed population?

For their ecological study they analyzed global data from the International Agency for Research on Cancer (IARC) for 2007 and the United Nations World Contraceptive Use 2007 report to correlate statistics on prostate cancer incidence and related deaths to use of contraceptives.

They analyzed the data by country and by continents, and they compared results from oral contraceptive use with all other forms of contraception, such as intra-uterine devices, condoms or vaginal barriers.

The results showed that:

  • Oral contraceptive use was significantly tied to prostate cancer incidence and related deaths in individual nations.

  • Oral contraceptive use was also linked to prostate cancer incidence in Europe.

  • There was no link between use of other forms of contraceptive and prostate cancer incidence or deaths.

  • Further analysis showed the links with oral contraceptive use did not depend on a country’s wealth.

Although the authors point out the study does not prove a cause and effect link, the findings suggest there is a need for further investigation, both to confirm them and to try and find out the chemical and biological pathways between possibles causes and effects.

In their discussion, they suggest one plausible explanation for the link between oral contraceptive use and prostate cancer is that the oral contraceptives in use today frequently contain high doses of ethinyloestradiol (an orally bio-active estrogen), that is “excreted in urine without degradation. This can then end up either in the drinking water supply or passed up the food chain”.

Written by Catharine Paddock PhD