17 November 2009

Common chemical found to feminize boys' brains

by Kate Melville

Adding to earlier investigations that linked two common phthalates to abnormal male genital development, the same researchers now say that those chemicals can also alter masculine brain development, making boys less likely to play with male-typical toys and games. The University of Rochester Medical Center (URMC) study, published in the International Journal of Andrology, examined phthalate levels in mothers' urine and the playground behaviors of their preschool boys.

Anti-androgens such as phthalates - which are pervasive in plastic products - have the potential to alter masculine brain development, said lead author Shanna H. Swan, director of the URMC Center for Reproductive Epidemiology. "Our results need to be confirmed, but are intriguing on several fronts," Swan explained. "Not only are they consistent with our prior findings that link phthalates to altered male genital development, but they also are compatible with current knowledge about how hormones mold sex differences in the brain, and thus behavior."

The major source of human exposure to the two phthalates of most concern (di(2-ethylhexyl) phthalate (DEHP) and dibutyl phthalate (DBP)) is through food. These phthalates are used primarily in polyvinyl chloride (PVC), so any steps in the processing, packaging, storage or heating of food that use PVC-containing products can introduce them into the food chain. Phthalates are also found in vinyl and plastic tubing, household products, and many personal care products such as soaps and lotions. Phthalates are increasingly associated with genital defects, metabolic abnormalities and reduced testosterone in babies and adults.

In the new study, higher concentrations of metabolites of DEH and DBP were associated with less male-typical behavior in boys on a standard play questionnaire. No other phthalate metabolites measured in-utero were linked to the less-masculine behavior. Girls' play behavior was not associated with phthalate levels in their mothers, the study noted.

The current study focused on a sample of mothers who delivered children between 2000 and 2003. At that time, the mothers provided urine samples around the 28th week of pregnancy. Swan speculated that phthalates may lower fetal testosterone production during a critical window of development - within 8 to 24 weeks gestation, when the testes begin to function - thereby altering brain sexual differentiation.

To further explore this notion, the researchers reconnected with the mothers and asked them to complete a standard research questionnaire, called the Preschool Activities Inventory (PSAI), for their children aged between 3-1/2 and 6-1/2.

The PSAI is designed to discriminate play behavior within and between the sexes, and in the past has been shown to reflect the endocrine-disrupting properties of other toxins, such as PCBs and dioxins. The PSAI addressed three aspects of play: the types of toys children choose (trucks versus dolls), activities (rough-and-tumble play, for example), and child characteristics.

Swan and her team then examined the boys play-behavior scores in relation to the concentration of phthalate metabolites in their mothers' prenatal urine samples and found that higher concentrations of DEHP and DBP metabolites were associated with less masculine play behavior scores.

Swan says that "phthalate syndrome" should be more thoroughly investigated and a deeper examination of how they impact the brain is warranted. "We have more work to do, but the implications are potentially profound," she concluded.

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Source: University of Rochester Medical Center