Background: Our research has shown significant associations between exposures to prenatal butylbenzyl phthalate (BBzP) and postnatal bisphenol A (BPA) and childhood asthma and other respiratory problems. Here we evaluate whether these endocrine disruptors interact to increase the risk of asthma, wheeze and urgent care visits. Methods: We measured monobenzyl phthalate (MBzP, metabolite of BBzP) in maternal prenatal spot urine and BPA in child spot urine at ages 3, 5 and/or 7 years among N=308 inner-city mother-child pairs in New York City. History of wheeze and urgent care visits was gathered by repeat questionnaire between child ages 5-11 years. Current asthma was diagnosed by a physician using standardized criteria. Children with no history of wheeze or other asthma-related symptoms were considered non-asthmatic. Mean of ages 3-7 BPA concentrations were calculated for each child. Models controlled for specific gravity and potential confounders. Results: Among children with postnatal BPA concentrations above but not below the median, maternal prenatal logeMBzP was associated with asthma and reported wheeze (p＜0.05). Similarly, among women with prenatal MBzP above but not below the median, child postnatal logeBPA was associated with asthma and wheeze (p＜0.05). Comparing subjects with prenatal MBzP and postnatal BPA above to those with one or both below the median, the relative risk was 1.73 (95% CI 1.24, 2.41) for current asthma, 1.92 (95% CI 1.17, 3.21) for early onset persistent wheeze, and 1.73 (95% CI 1.29, 2.48) for urgent care visits. The interactions between MBzP and BPA were significant for asthma (p=0.03) and any report of wheeze between ages 5-11 years (p=0.045). Conclusion: Results suggest a significant interaction between prenatal MBzP and postnatal BPA on child asthma and wheeze, and the possibility of a 'two-hit model' where higher BBzP exposure during pregnancy may render the child more susceptible to the effects of BPA exposure in early childhood.
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