Association Between Early Life Exposure to Phthalates and Organophosphate Esters and the Development of Childhood Asthma and Wheeze

Asthma is the most common chronic disease among children. Children spend most of their early life indoors, exposed to chemicals used in consumer and building products, which may present a risk to asthma development, including phthalates, used as plasticizers, and organophosphate esters (OPEs), used as flame retardants and plasticizers. Few epidemiological studies have examined early life exposure to these chemicals and the development of childhood asthma, as well as the interplay with genetics, which was examined by this dissertation using data from the Canadian CHILD Cohort Study. Using urine samples from 1,578 children collected across early life and 726 house dust samples collected at 3-4 months, I found that Canadian children have ubiquitous early life exposure to phthalates and OPEs. I found higher phthalate metabolite concentrations among children in lower income families. OPE concentrations were higher in dust collected here compared to other studies, possibly due to sampling of the child’s sleeping environment that contains sources of OPEs and phthalates. Using a case-cohort study, I examined the association between early life exposure to phthalates and OPEs, measured in house dust samples collected at 3-4 months, and the development of asthma at 5 years and recurrent wheeze between 2 to 5 years. I found a four-fold increased risk of asthma associated with the highest concentration quartile of di(2-ethyl-hexyl) phthalate (DEHP) and a two-fold increased risk of recurrent wheeze across all quartiles of DEHP compared to the lowest quartile. For OPEs, I observed a two to four-fold increased risk of asthma diagnosis across quartiles of tris(2-butoxyethyl) phosphate exposure compared to the lowest quartile. Using a Genetic Risk Score (GRS) combining multiple genetic loci, I examined whether genetics modifies the association between early life phthalate exposure and the risk of childhood asthma and recurrent wheeze. The GRS did not modify the association with childhood asthma or recurrent wheeze. These results highlight the need to reduce exposure to phthalates and OPEs during early life, especially the first year of life, and the importance of exposures among low-income populations and within the sleeping microenvironment.Ph.D