Nov. 16, 2009 -- Mothers exposed to high levels of chemicals known as phthalates during pregnancy may have boys who are less likely to play with trucks and other male-typical toys or to play fight, according to a new study.
Phthalates, common in the environment, are found in toys, food packaging, personal care products, nail polish, adhesives, and other products.
In the study, the researchers focused on two phthalates of concern to environmental experts, DEHP and DBP. They tested the urine of women during the 28th week of pregnancy and divided them into four groups depending on the concentration of phthalate metabolites or breakdown products. Then they assessed the play behavior of the 145 children when they reached age 3 to 6.
If mothers were in the highest concentration group, the chance that their boys had a less masculine score was five times greater than mothers in the lowest concentration group, according to study researcher Shanna Swan, PhD, professor of obstetrics and gynecology at the University of Rochester Medical Center's Center for Reproductive Epidemiology and an expert on phthalates.
''I'm not saying these boys are feminized," Swan tells WebMD. Rather, she says, ''they are less likely to play in a male-typical manner." No effect was found with the girls.
Swan and other experts suspect that exposure to the chemicals affects the level of testosterone crucial for the development not only of male reproductive organs, but also the masculine brain. ''We now suspect that the phthalate [exposure] affects the entire body, not just the reproductive tract,'' Swan says.
The study is published in the International Journal of Andrology.
Exposure to Phthalates
Swan and her colleagues tested urine samples of 74 pregnant women who gave birth to boys and 71 who gave birth to girls, looking for nine different phthalates. The women were part of The Study for Future Families, an ongoing study.
When the children were ages 3.6 to 6.4 years, Swan's team asked the mothers to answer questions about their children's play behavior. Parents described the type of toys and play their children favored, and each child was given a score reflecting masculine-typical play or feminine-typical play.
Exposure to two of the nine phthalates, DEHP and DBP, was associated with less masculine play behavior, the researchers found.
For example, Swan says, ''If the mother's MEHHP concentration [one of the phthalate metabolites] was high, in the upper quartile, the odds that her boy had a score that was less masculine [in play behavior] was five times greater than mothers whose MEHHP was in the lowest quartile."
Exposure to phthalates may lower testosterone production in the fetus during a crucial period of development, at about 8 to 24 weeks' gestation, Swan says, when the testes begin to function, and in doing so alter sexual differentiation in the brain.
The study results should be a wake-up call about the potential dangers of phthalate exposures, according to Sarah Janssen, MD, PhD, MPH, staff scientist at the Natural Resources Defense Council, who reviewed the study results for WebMD.
''This study by itself shouldn't make parents panic, but I do think we are beginning to accumulate more and more evidence that exposure to phthalates, especially during pregnancy, can be harmful for the development of baby boys," she says.
Janssen cites animal studies, finding that exposure to the chemicals can cause a wide range of male reproductive harm, including undescended testicles, birth defects of the genitals, and infertility later in life.
"What this study adds is, we know testosterone and estrogen are also very important for the development of the brain and sexual differentiation of the brain,'' she says. The new study suggests that interfering with testosterone levels during critical periods of development can affect later behavior, she says.
Advice for Moms-to-Be
Limiting exposure to the chemicals is best, say Swan and Janssen, although the chemicals are ubiquitous.
Under a federal law passed in 2008, the Consumer Product Safety Improvement Act, six phthalates are now banned from use in toys such as bath toys, dolls, and teethers. Some products carry a "No phthalates" label.
One way to avoid exposure, Janssen says, is to avoid heavily fragranced shampoos and lotions as well as air fresheners.
What's needed next, according to Janssen, is more attention on limiting exposure to the chemicals to women who are pregnant or those of childbearing age.
Swan's study was funded by the National Institutes of Health, the Environmental Protection Agency, and the State of Iowa.