Mothers' exposure to phthalates linked to un-masculine play in young boys

A pilot study led by Dr Shanna Swan, professor of obstetrics and gynecology and director of the of the University of Rochester Medical Center in New York found that young boys whose mother's urine when they were in the womb contained higher levels of two phthalates, common chemicals present in PVC used in food packaging and storing, were less likely to engage in play fighting and play with masculine toys such as trucks.

Phthalates are a family of organic chemicals, made from oil, used to make plastics such as polyvinyl chloride (PVC) softer and more flexible, They have been around for about 50 years and are the most commonly used plasticisers in the world present in vinyl and plastic tubing, household products, and personal care products such as soaps and lotions. They are considered controversial because more and more studies are linking them with genital defects, metabolic abnormalities, and reduced testosterone in babies and adults.

In the US, a federal law passed in 2008 banned 6 phthalates from being used to make children's items such as teethers, soft books, bath toys, dolls and plastic figures.

Dr Swan and her team have previously shown that phthalate exposure during pregnancy might affect the development of genitals of both male rodents and baby boys, and scientists call this cluster of genital alterations the ‘phthalate syndrome’.  Recent studies have highlighted particular concerns about human exposure to di(2-ethylhexyl) phthalate (DEHP), and dibutyl phthalate (DBP) via the food chain. DEHP and DBP are used primarily in the manufacture of PVC and exposure can occur when food is processed, packaged, stored, or heated. Researchers are concerned because phthalates are anti-androgens and have the potential to alter the development of the masculine brain, which depends on the presence of the androgen testosterone.

Since 1998 Swan, has been leading the federally funded, multi-center Study for Future Families (SFF), which is collecting a large database of information to help scientists investigate toxins.

For this study, Swan and colleagues used data from a subset of SFF mothers who gave birth between 2000 and 2003 and who around the 28th week of pregnancy gave urine samples that were analysed for phthalate metabolites by the US Centers for Disease Control and Prevention (CDC). These mothers were asked to complete a standard research questionnaire, called the Preschool Activities Inventory (PSAI), for their 145 children aged from 3.5 to 6.5 years.

The PSAI differentiates play behavior within and between the sexes, and past studies have shown it reflects the endocrine-disrupting properties of other toxins, such as PCBs and dioxins, highlighting types of toys children choose (eg trucks versus dolls), activities (eg rough-and-tumble play), and child characteristics.

The results showed that:
Higher levels of metabolites of two phthalates, DEHP and DBP, were linked to less male-typical behavior in boys.No other phthalate metabolites measured in their mother's urine linked to the less-masculine behavior.Girls' play behavior was not linked with phthalate levels in their mothers' urine.

This was only a pilot study, but the implications are profound as not only are they consistent with prior findings that link phthalates to altered male genital development, but they also are compatible with current knowledge about how hormones mould sex differences in the brain, and thus behaviour.

The researchers suggest that phthalates may lower fetal testosterone production during a critical window of development, somewhere between weeks 8 and 24 of gestation, when the testes begin to function, and this affects brain sexual differentiation.

With previous studies suggesting that hormone disrupters like phthalates can impair genital development and hormones in the body, and this study linking play-behaviour with fetal phthalate exposure, there is now a need for research that explores more deeply how these chemicals potentially disrupt the sexual development of the brain.

International Journal of Andrology

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First Published in November 2009


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