17 November 2009

Apparently, some chemicals make boys act like girls

In a recent study from the University of Rochester in New York, published in the International Journal of Andrology, Professor of obstetrics and gynaecology Shanna Swan found that some chemicals such as phthalates made boys who were exposed to them in utero behave as girls. Abstract
Prenatal phthalate exposure and reduced masculine play in boys

Correspondence to Shanna H. Swan, Department of Obstetrics and Gynecology, University of Rochester School of Medicine and Dentistry, 601 Elmwood Avenue, Box 668, Rochester, NY 14624, USA.
E-mail: shanna_swan@urmc.rochester.edu

Foetal exposure to antiandrogens alters androgen-sensitive development in male rodents, resulting in less male-typical behaviour. Foetal phthalate exposure is also associated with male reproductive development in humans, but neurodevelopmental outcomes have seldom been examined in relation to phthalate exposure. To assess play behaviour in relation to phthalate metabolite concentration in prenatal urine samples, we recontacted participants in the Study for Future Families whose phthalate metabolites had been measured in mid-pregnancy urine samples. Mothers completed a questionnaire including the Pre-School Activities Inventory, a validated instrument used to assess sexually dimorphic play behaviour. We examined play behaviour scores (masculine, feminine and composite) in relationship to (log10) phthalate metabolite concentrations in mother's urine separately for boys (N = 74) and girls (N = 71). Covariates (child's age, mother's age and education and parental attitude towards atypical play choices) were controlled using multivariate regression models. Concentrations of dibutyl phthalate metabolites, mono-n-butyl phthalate (MnBP) and mono-isobutyl phthalate (MiBP) and their sum, were associated with a decreased (less masculine) composite score in boys (regression coefficients −4.53,−3.61 and −4.20, p = 0.01, 0.07 and 0.04 for MnBP, MiBP and their sum respectively). Concentrations of two urinary metabolites of di(2-ethylhexyl) phthalate (DEHP), mono-(2-ethyl-5-oxohexyl) phthalate (MEOHP) and mono-(2-ethyl-5-hydroxyhexyl) phthalate (MEHHP) and the sum of these DEHP metabolites plus mono(2-ethylhexyl) phthalate were associated with a decreased masculine score (regression coefficients −3.29,−2.94 and −3.18, p = 0.02, 0.04 and 0.04) for MEHHP, MEOHP and the sum respectively. No strong associations were seen between behaviour and urinary concentrations of any other phthalate metabolites in boys, or between girls' scores and any metabolites. These data, although based on a small sample, suggest that prenatal exposure to antiandrogenic phthalates may be associated with less male-typical play behaviour in boys. Our findings suggest that these ubiquitous environmental chemicals have the potential to alter androgen-responsive brain development in humans.
Surely using type of play as a measure raises questions about judgmental assumptions about behaviour. The only scientific measure should only be of testosterone levels. Measuring behaviour such as play, based on stereotyped gender roles raises more questions about nature versus nurture.

Research findings were widely reported including by BBC, Time, etc. None of the media reports challenged the assumptions made about stereotyped behaviour.

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