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