Early life exposure to phthalates and the development of childhood asthma among Canadian children

BACKGROUND: Studies have demonstrated an association between phthalate exposure and childhood asthma, although results have been inconsistent. No epidemiological studies have examined exposure during the first year of life. OBJECTIVE: To investigate the association between phthalate exposures in the home environment during the first year of life, and subsequent development of childhood asthma and related symptoms. METHODS: This study used a case-cohort design including 436 randomly selected children and all additional cases of asthma at 5 years (n_total = 129) and recurrent wheeze between 2 and 5 years (n_total = 332) within the CHILD Cohort Study, a general population Canadian birth cohort of 3455 children. Phthalate exposure was assessed using house dust samples collected during a standardized home visit when children were 3-4 months of age. All children were assessed by specialist clinicians for asthma and allergy at 1, 3 and 5 years. Logistic regression was used to assess the association between exposure to five phthalates and asthma diagnosis at 5 years, and recurrent wheeze between 2 and 5 years, with further stratification by wheeze subtypes (late onset, persistent, transient) based on the timing of onset and persistence of wheeze symptoms. RESULTS: Di(2-ethylhexyl) phthalate (DEHP) had the highest concentration in dust (median_subcohort = 217 μg/g), followed by benzyl butyl phthalate (BzBP) (20 μg/g). A nearly four-fold increase in risk of developing asthma was associated with the highest concentration quartile of DEHP (OR = 3.92, 95% CI: 1.87-8.24) including a positive dose-response relationship. A two-fold increase in risk of recurrent wheeze was observed across all quartiles compared to the lowest quartile of DEHP concentrations. Compared to other wheeze subtypes, stronger associations for DEHP were observed with the late onset wheezing subtype, while stronger associations for di-iso-butyl phthalate (DiBP) and BzBP were observed with the transient subtype. DISCUSSION: DEHP exposure at 3-4 months, at concentrations lower than other studies that reported an association, were associated with increased risks of asthma and recurrent wheeze among children at 5 years. These findings suggest the need to assess whether more stringent regulations are required to protect children's health, which can be informed by future work exploring the main sources of DEHP exposure.