Abstract
INTRODUCTION: Throughout the perinatal period children are exposed to complex mixtures, including indoor chemicals such as phthalates, and biological agents. However, few studies focus on interactions between early-life co-exposures to shed light on how co-exposures modify their individual effects. Therefore, our study aims to assess whether early-life exposure to pets and related biological agents, namely pet allergens and endotoxin, modifies the association between di-(2-ethylhexyl) phthalate (DEHP) and asthma and wheeze in preschoolers to gain insight into interactions. METHODS: Using data from a Canadian birth cohort study (CHILD), we conducted two complementary analyses on respiratory outcomes. First, we combined pet ownership with DEHP measurements from house dust (N = 726). Second, we focused on a subgroup of children with exposure measurements of both DEHP and biological agents in dust (N = 261). We used multivariable logistic regression models to assess whether pets and quantified biological agent levels modify associations between DEHP and asthma at 5 years and recurrent wheeze between 2 and 5 years. Interaction terms were included in the models and stratified analyses were further conducted. RESULTS: Associations between DEHP and asthma and wheeze were modified by pet ownership and related biological agents. For persistent/recurrent wheeze, the association with DEHP became larger among children with dogs at home and with higher dog allergens (p-interaction <0.1) and became smaller and insignificant when exposed to cats. Similarly, for asthma, the association with DEHP tended to be larger among children with dogs (also higher dog allergens) and among children without cats (also lower cat allergens) at home, respectively. Endotoxin levels modified the association between DEHP and persistent wheeze (p-interaction <0.1). CONCLUSIONS: Early-life exposure to pets and related biological agents may modify the associations between phthalates and asthma and wheeze in children. Heterogeneity in single exposure studies could be a result of differences in co-exposures among studies.