Effects of early‐life exposure to dust mite allergen and endotoxin on the development of asthma and wheezing: The Japan Environment and Children's Study

BACKGROUND: The effects of early‐life exposure to house dust mite allergen and endotoxin on the development of asthma are unclear in the literature. We investigated the association of early‐life exposure (0–36 months old) to house dust mite allergen and endotoxin with asthma incidence. METHODS: In this novel, large‐scale, nationwide birth cohort study, 5017 participants were randomly selected from those who met the eligibility criteria. House dust was vacuum‐sampled from the children's mattresses within homes and assayed for the presence of dust mite allergen (Der 1) and endotoxin. The participants were classified into four quartiles (Q1–Q4) according to exposure levels. We defined the incidence of asthma and wheezing using questionnaires at 12, 24, and 36 months old. Odds ratios (ORs) of the incidence of asthma and wheezing by age in Der 1 and endotoxin exposure level were estimated using logistic regression. RESULTS: The cumulative incidence rates of asthma and wheezing during 0–36 months were 10.4% and 38.1%, respectively. Significant ORs were observed in asthma onset during 12–24 months old, asthma onset during 24–36 months old, and wheezing onset during 0–12 months old in the Q4 Der 1 group. In the Q4 endotoxin group, significant positive associations between endotoxin exposure and asthma (OR 2.00, 95% confidence interval [CI]: 1.03–3.85) and wheezing (OR 1.78, 95% CI: 1.01–3.12) onset during 24–36 months old were found. CONCLUSIONS: Our results indicated that high levels of early‐life exposure to Der 1 and endotoxin in mattresses may be involved in the development of asthma.