A team of U.S. endocrinologists recently published the results of a meta-analysis examining a possible association between bisphenol A (BPA) and childhood ADHD. BPA is used in a variety of consumer products, including plastic bottles for food and drink, epoxy resins used to line cans of food, dental sealants, and the thermal receipts issued by stores.
A review of the literature found 29 rodent studies but only three with humans. The human studies were too different from each other to be suitable for meta-analysis. One found no association between prenatal exposure and ADHD. A second found prenatal BPA exposure to be associated with teacher-reported hyperactivity in 4-year-old boys, but not girls. The third found it to be associated with hyperactivity scores in 3-year-old girls.
As the authors note, “Often, there is little human data available, particularly in the environmental toxicology/health fields, due to the time and expense of conducting epidemiological studies and the ethical barriers for human controlled trials that involve human exposure to potentially hazardous chemicals. Thus, it is important to have methods for using animal data to inform human health hazard conclusions; indeed, animal models are traditionally used to study human health.”
Twelve of the mice and rat studies, with a total of 709 rodents, were suitable for meta-analysis.
Overall these pointed to a tiny SMD effect size of 0.09, but it was not significant, with the odds of such a result being obtained by chance being almost one in four (p = 0.237). But when results from the 356 males and 353 females were looked at separately, a significant sex difference emerged. There was essentially no effect on female rodents, with an effect size of -0.07 and a 95% confidence interval of -0.27 to 0.14, widely spanning the zero mark, rendering the result statistically nonsignificant. Among male rodents, however, there was a small but statistically significant effect size (0.24), with a 95% confidence interval from 0.04 to 0.45. The odds of obtaining this outcome by chance were only one in 50 (p = .02).
This result must be viewed with caution, as rodent physiology often differs substantially from that of humans. The authors therefore conclude, “early BPA exposure is associated with a presumed hazard of hyperactivity in humans. Our conclusion is based on ‘moderate’ levels of evidence for the human and ‘high’ levels of evidence for animal literature.”
REFERENCES
Johanna R. Rochester, Ashley L. Bolden, Carol F. Kwiatkowski, “Prenatal exposure to bisphenol A and hyperactivity in children: a systematic review and meta-analysis,” Environment International, vol. 114, p. 343-356 (2018).