Autistic spectrum disorder, attention deficit hyperactivity disorder, and allergy: Is there a link? A nationwide study

• Children with ADHD or ASD had an increased risk of allergic comorbidities.
• Children with both ADHD and ASD had the highest risk of allergic comorbidities.
• ASD children with more allergic comorbidities were associated with a greater likelihood of ADHD.

Previous studies showed that both attention deficit hyperactivity disorder (ADHD) and autistic spectrum disorder (ASD) were associated separately with a higher risk of allergic diseases. However, the comorbid effect of ADHD and ASD on the risk of allergic diseases is still unknown. Using the Taiwan National Health Insurance Research Database, 5386 children aged less than 18 years with ADHD alone, 578 with ASD alone, 458 with ADHD + ASD, and 25,688 non-ADHD/ASD age- and sex-matched (1:4) controls were enrolled in our study. The prevalence of allergic diseases, including asthma, allergic rhinitis, atopic dermatitis, and allergic conjunctivitis, was evaluated among the four groups. Logistic regression analysis showed that the ADHD + ASD group (odds ratio [OR]: 2.26, 95% confidence interval [CI]: 1.83–2.79), ADHD-alone group (OR: 1.81, 95% CI: 1.70–1.93), and ASD-alone group (OR: 1.24, 95% CI: 1.04–1.48) had an increased risk of allergic comorbidities compared to the control after adjusting age, sex, and level of urbanization. ASD children with more allergic comorbidities (≧3: OR: 2.57, 95% CI: 1.74–3.79; 2: OR: 2.00, 95% CI: 1.41–2.84; 1: OR: 1.60, 95% CI: 1.16–2.22) were associated with a greater likelihood of ADHD. Children with ADHD or ASD had an increased risk of allergic comorbidities, and those with both ADHD and ASD had the highest. These results may inspire more research to clarify the underlying mechanisms among ASD, ADHD, and allergic diseases.