Release Date: February 14, 2003
BUFFALO, N.Y. -- Women's exposure to environmental contaminants that mimic the activity of human sex hormones during prenatal development can affect the masculinity and femininity of their offspring, UB researchers have found.
However, the results seem to point to a shared influence of the parents' own gender-related behavior and exposure to the contaminants, which can act as "endocrine disrupters," according to David E. Sandberg, Ph.D., UB associate professor of psychiatry and pediatrics and lead author on the research.
The study appears today (Feb. 14, 2003) in the journal Epidemiology. It supports the findings of an October study done in the Netherlands, which was the first to show a relationship between exposure to hormonally active agents in the environment and children's gender-role behavior.
The UB study reports on gender behavior of boys and girls born to male and female anglers and their spouses who eat contaminated sport fish from the Great Lakes.
Their findings show that in boys, the more fish the mother consumed, the more typically masculine the boy's behavior. Girls with one or more older siblings also showed more masculine behavior. In an interesting twist, results showed that girls who were breastfed longer showed more typically feminine behavior.
Sandberg and colleagues set out to assess the relationship between gender behavior and exposure to toxins that have potential to influence the action of natural estrogens and androgens at sensitive periods of sexual differentiation in the womb. Their study group was composed of participants in the New York State Angler Cohort Study -- men and women from 16 counties who consumed contaminated sport fish from Lake Ontario and its tributaries. Earlier research with this group showed that their PCB body burden was 2-to-4 times higher than that of the general population.
The children studied, 729 boys and 672 girls between the ages of 6 and 10, all were offspring of women in the Angler Cohort. A parent, in most cases the mother, completed a survey designed to assess the amount of typically masculine or typically feminine behavior the child exhibited.
While the increase in mother's years of eating fish from contaminated waters was associated with more masculine behavior in boys, Sandberg said this effect doesn't appear to be related to prenatal exposure, for several reasons.
"First, hormonally active toxins from the environment classified as endocrine disrupters, as is the case here, are known to interfere with androgens' masculinizing effects, rather than promoting them," he said. "Second, if these chemicals were acting as androgens (the masculinizing hormone), the girls' behavior would be masculinized as the level of contaminant exposure increased, and this was not the case." Finally, he noted, any potential masculinizing effect of these chemicals would be overwhelmed by the ample androgens produced by the fetal testis.
Instead, Sandberg and colleagues theorize that the more masculine behavior of boys whose mothers had consumed more sport fish is the consequence of the social environment, rather than toxic exposure.
"Our speculation is that anglers and their spouses who consume larger quantities of sport fish may encourage more typically masculine behavior in their sons," he said.
Sandberg went on to explain that an effect of contaminant exposure might have been observed in the girls. "Androgens normally transferred from the mother to the female fetus are believed to contribute to varying degrees of normal masculine behavior in daughters, an effect that may be disrupted by exposure to toxins in the fish.
"We drew this conclusion from the finding that female study participants with older sisters were more masculine in their behavior than were first born. Because mothers transfer large quantities of their body burden of pollutants to their offspring during pregnancy and breast-feeding, a later-born daughter would be exposed to relatively less endocrine disrupting chemicals, resulting in more masculine behavior," he noted. "In contrast, an earlier-born daughter, who would be exposured to more endocrine disruption in the womb, would be more 'feminized.'"
The social environment appeared to be no less important for the girls than for the boys, and likely was the reason for increased feminine behavior of girls who were breastfed longer, Sandberg said.
"We speculate that mothers who breastfeed are likely to be more traditional in their gender-role behavior than women who don't, and that their daughters' behaviors reflect this."
A biological influence of contaminated breast milk on gender development was unlikely, Sandberg observe, because sex hormones are thought to exert a gender-organizing effect only prenatally.
"A major limitation of our study was that we assessed only one side of the picture, the exposure side, which influences the biology of the child," Sandberg said. "We need to assess the social and family environment, as well, in an effort to tease out the relative contributions of these two sets of factors in the development of gender differences in behavior."
John E. Vena, Ph.D., John Weiner, Ph.D., Gregory P. Beeler, doctoral student, and Mya Swanson, all of the UB School of Medicine and Biomedical Sciences, and Heino F.L. Meyer-Bahlburg of Columbia University, also contributed to the study.
The research was funded in part by the National Institute of Environmental Health Sciences (National Institutes of Health), the Great Lakes Protection Fund, and the Agency for Toxic Substances and Disease Registry.