Exposure to endocrine-disrupting chemicals (EDCs) in the first trimester of pregnancy may affect intellectual functioning in childhood, according to study results published in Environment International. This relationship between prenatal EDC exposure and IQ was found only among boys.
It is known that EDCs may affect neurodevelopment and behavior in children, but most research thus far has studied single chemicals in isolation, which does not accurately represent the potential harms of co-exposures that humans are vulnerable to in reality.
Using weighted quantile sum regression, researchers assessed the effect of prenatal exposure to 26 EDCs on cognitive function, hypothesizing that greater overall exposure to a mixture of EDCs would be correlated with lower IQ scores in childhood.
Mother-child pairs (N=718) were selected from the Swedish Environmental Longitudinal Mother and Child, Asthma and Allergy study for inclusion in the analysis. Maternal blood and urine samples were collected at first prenatal visit (median 10 weeks pregnancy) and measured for a total of 54 analytes, including phenols, plasticizers, perfluoroalkyl substances, and persistent chlorinated compounds. After exclusions and summations, 26 chemicals were analyzed. In a multivariable linear model, the overall effect of the mixture of EDCs was expressed by a unidirectional weighted quantile sum index.
The Wechsler Intelligence Scale for Children, 4th edition full-scale IQ was used to evaluate cognitive function in children at age 7 years. Maternal IQ was also measured and adjusted for in statistical models.
The researchers found that for each interquartile range change in EDC weighted quantile sum index, IQ at age 7 years declined by 2.2 points (95% CI, -3.4 to -1.0 points) among all children, 3.6 points (95% CI, -5.3 to -2.0 points) in boys, and 1.8 points (95% CI, -3.5 to 0.0 points) in girls.
To evaluate the generalizability of their findings, the researchers conducted repeated holdout validation, a machine learning method that combines cross-validation and bootstrap resampling.
They found that the inverse association between EDC exposure and IQ followed a similar pattern in this validation analysis (decline of 0.8 IQ points among all children, 1.9 IQ points in boys, and no decline for girls for each interquartile range change in EDC weighted quantile sum index), but overall the association was attenuated.
Of all 26 chemicals, bisphenol F had the greatest relative impact on neurodevelopment in boys. This newer bisphenol formulation is used as an alternative to bisphenol A (BPA) but may not be any safer, according to these findings. BPA was also identified as a chemical of concern among boys, as were short-lived pesticides, plasticizers, and perfluoroalkyl substances.
“We identified mostly short-lived pollutants as chemicals of concern,” wrote the investigators, “suggesting that interventions to abate current exposure among pregnant women or women trying to become pregnant may mitigate the potentially harmful neurodevelopment impacts of prenatal EDC exposure.”
“Further evaluation of EDC influences on specific domains of cognitive functioning may illuminate underlying biological mechanisms, leading to more specific preventive interventions for mothers and children,” they concluded.
Tanner EM, Hallerbäck MU, Wikström A, et al. Early prenatal exposure to suspected endocrine disruptor mixtures is associated with lower IQ at age seven [published online October 24, 2019]. Environ Int. doi:10.1016/j.envint.2019.105185