Oestrogen-like chemicals commonly found in oral contraceptives and plastic packaging could deform the prostate gland of human embryos, suggests a new study in mice. Deformities to the prostate gland have been linked to prostate cancer and bladder disease in later life.

The finding is significant because up to 3% of women taking oral contraceptive drugs become pregnant without their knowledge, and continue exposing the fetus to the contraceptive drug many months into pregnancy.

This is because the risk of pregnancy becomes higher when the drug is not taken diligently, but many women do not realise this, says study author Frederick vom Saal of the University of Missouri in Columbia, US.

Among the 60 million women using oral contraceptives in the US and Europe, the average number of missed pills is three per month, he says. This results in up to two million women taking the pill accidentally becoming pregnant each year.

Environmental pollutant

In order to test the effect of a typical oral contraceptive on the development of the embryo, vom Saal and his team gave pregnant mice the contraceptive ethinylestradiol. The dosage was scaled down to the mouse-equivalent of one-fifth of the normal human dose and was administered for five days.

They also exposed a group of mice to low levels of a similar oestrogenic chemical, bisphenol A - a common environmental pollutant found in polycarbonate plastics and the lining of food cans.

The researchers found a subsequent increase in the number and size of prostate ducts and a narrowing of the bladder neck in male mouse fetuses exposed to these chemicals.

The effect seen was similar to the deformities caused by diethylstilbestrol - a known teratogenic and cancer-causing chemical also tested by the team. That drug caused cancer and other reproductive organ abnormalities in children born in the 1950s and 60s after it was administered to their mothers while pregnant.

The researchers argue that the effect seen in mice - which could lead to difficulties with urination as well as prostate cancer - is a direct analogue of how these drugs affect the human reproductive system.

Synthetic hormones

“These chemicals [mimic] extremely potent synthetic sex hormones, strong enough to completely control an adult women’s reproductive system,” vom Saal stated: “The developing fetus is extremely sensitive to chemical disturbance…so exposing a male baby to them is a very bad idea.”

“These interesting results add to the evidence that these chemicals can damage human embryos,” comments endocrinologist Stephen Safe at Texas A&M University in College Station, US. Though more studies are needed to confirm the mouse strain tested is a good analogue of the human reproductive system, the findings justify a careful re-evaluation of the safety of these chemicals, he says.

Journal reference: Proceedings of the National Academy of Sciences (DOI: 10.1073/pnas.0502544102)