Wednesday, October 20, 1999 Published at 22:53 GMT 23:53 UK
Premature puberty for chemically-exposed mice
The mouse study should "serve as a guide for human research"
By environment correspondent Alex Kirby
US scientists claim to have found evidence that some of the reproductive and weight problems seen in western societies in recent years may be the result of exposure to a chemical used to make everyday plastics.
The researchers exposed unborn mice to bisphenol A (BPA) which is employed in the manufacture of polycarbonate plastic products such as baby bottles, tin can linings, some toys and certain types of food storage containers.
The chemical leaches out of the plastic at a rate that increases with use. In the human body, it can mimic the effects of the sex hormone oestrogen. It is one of a number of so-called endocrine disrupters that can upset the hormonal system and are causing concern among environmentalists.
The team of scientists from the University of Missouri-Columbia and North Carolina State University say the mice experienced premature puberty and an increase in body weight shortly after birth.
In their experiments the researchers used quantities of BPA typical of the levels to which humans are routinely exposed. The mice were exposed only during pregnancy, not after birth. The exposed mice weighed 20% more than normal when examined at puberty.
The conclusion of the researchers is that BPA somehow programs post-natal growth.
"We found that the largest effects happened to the babies of the pregnant mother," says Kembra Howdeshell, one of the lead researchers.
"The chemical did not affect the mother, but instead it altered the babies' growth patterns and accelerated timing of sexual maturity. Our study shows that this chemical may be a factor for contributing to trends seen in human populations over the past several decades."
The team, who have reported their work in the journal Nature, are now calling for more human research.
"We're not offering an answer concerning effects in humans with these findings; instead, the findings pose a question regarding human health," says co-researcher Professor Frederick vom Saal.
"This study should serve as a guide for human research.
"We believe that the medical community should take a long look at this study and consider looking at BPA as a possible cause for the changes in growth, sexual maturation and reproductive abnormalities that have been reported in the humans."
In both humans and animals, the team says there is significant variability in responsiveness to environmental estrogens, and that one source of this variability may be the amount of sex hormones to which the foetus is exposed.
They say their experiments show that this can be influenced by factors such as the size of the placenta and how many foetuses are in the womb.