BioEd Online

Pregnant women could be unwittingly exposing their unborn children to harmful amounts of the hormone oestrogen. Researchers have demonstrated that tiny quantities of this hormone, found in birth-control pills and some plastics, can cause serious deformities in male mouse fetuses.

"There should be a much higher level of concern," says Frederick vom Saal, a biologist at the University of Missouri, Columbia, who headed the study.

Oestrogenic drugs have long been known to cause problems. Since the 1990s, the work of vom Saal and others has revealed links between these drugs and sperm production, sex reversal in amphibians, early onset of puberty and a variety of behavioural changes.

Not all of the evidence is confined to lab studies. For example, many women prescribed an anti-miscarriage oestrogenic drug called diethylstilbestrol in the 1950s gave birth to babies who later developed genital abnormalities.

Vom Saal wanted to study the impact of common oestrogens on fetal development. These chemicals include bisphenol A, an artificial compound with oestrogenic properties that is used in the hard plastic lining of tin cans. When tins are exposed to high temperatures, this chemical may leach into food.

The team also looked at the oestrogenic component of birth-control pills, called ethinyl estradiol. About 3% of the 60 million women in the United States and Europe on birth control are estimated to become unintentionally pregnant while taking these drugs.

Small dose, big effect

Vom Saal and his team fed pregnant mice a daily dose of 0.1 micrograms of ethinyl estradiol per kilogram of their weight. That is about twice as much as a typical woman on the birth control pill ingests. They also gave other mice a regular bisphenol A dosage of 10 micrograms per kilogram. The US government suggests people consume a maximum of five times this amount.

The male mice born to mothers given bisphenol A had 41% more ducts in their prostate glands than the control mice, the researchers found. Both ethinyl estradiol and DES produced a 25% increase in such ducts. The researchers suggest that increased exposure to synthetic oestrogen in the womb programs the cells of the prostate gland to become hyperactive. The resulting enlargement of the gland can cause serious discomfort later in life.

"Prostate enlargement affects half of all UK men over the age of 50," notes Debbie Thompson, information manager at The Prostate Cancer Charity in London. "It can make it more difficult to urinate and it can often lead to further problems such as impotence."

The researchers say the results are somewhat surprising. Because bisphenol A is not used for its sex-hormone effects, they expected the oestrogenic impacts to be smaller. "We had expected it to be 100 times less potent than the other two, but it caused a much bigger effect," says vom Saal. Their paper appears in the Proceedings of the National Academy of Sciences¹.

Vom Saal notes that a growing body of evidence against bisphenol A has led California lawmakers to consider banning the chemical from plastics used in baby products. He hopes that others will consider similar action.