Early childhood allergy linked with development of attention deficit hyperactivity disorder and autism spectrum disorder.

BACKGROUND: Previous studies reported controversial results regarding the association between allergic disorders and attention deficit hyperactivity disorder (ADHD)/autism spectrum disorder (ASD). The aim of this article was to investigate whether allergic disorders are associated with ADHD/ASD in a large cohort of pediatric patients. METHODS: A retrospective study using the pediatric (0-18 year) database (ICD-9-CM codes) of Clalit Health Services during the years (2000-2018). Diagnosis of all disorders was made by specialist physicians. RESULTS: A total of 117 022 consecutive non-selective allergic children diagnosed with one or more allergic disorder (asthma, rhinitis, conjunctivitis, skin, food, or drug allergy) and 116 968 non-allergic children were enrolled to our study. The mean follow-up period was 11 ± 6 years. The presence of allergic disorders in early childhood (mean age of allergic diagnosis 4.5 ± 4.3 years) in boys as well as in girls significantly increased the risk to develop ADHD (O.R 2.45, CI 2.39-2.51; p < .0001), ASD (O.R 1.17, CI 1.08-1.27; p < .0001), or both ADHD + ASD (O.R 1.5, CI 1.35-1.79; p < .0001). Children with more than one allergic comorbidity revealed a much higher risk. In a multivariable analysis (adjusted for age at study entry, number of yearly visits, and gender), the risk of allergic children to develop ADHD and ADHD + ASD, but not ASD alone, remained significantly higher. CONCLUSION: Allergic disorder in early childhood significantly increased the risk to develop ADHD, and to a less extend ASD, in later life.