An international team of researchers has carefully examined the best current evidence and found strong evidence for an association between asthma and ADHD by combining a meta-analysis of prior data with a new analysis of the Swedish population.
The meta-analysis identified 46 datasets with a total of more than 3.3 million persons. It computed an unadjusted odds ratio (OR) of 1.7, which indicates that ADHD patients have about twice the risk of developing asthma compared with people without ADHD. Limiting the meta-analysis to studies that adjusted for confounding factors, 30 datasets with more than a third of a million participants still led to an adjusted odds ratio of 1.5 (95% CI 1.4 – 1.7). The likelihood of obtaining this result by chance in such a large sample would be less than one in ten thousand.
When the team further checked this result against the results for the Swedish population ofmore than one and a half million persons, the odds ratio was an almost identical 1.6. Adjusting for confounding factors reduced it to 1.5 (95% CI 1.41 – 1.48). That means the findings are very robust: asthma and ADHD are associated, with an odds ratio of 1.5, after adjusting for confounding factors.
What does this small but statistically very reliable association between asthma and ADHD mean? For researchers, it suggests that the two disorders may have common risk factors and that the search for these shared risk factors might lead to improved treatments. These risk factors might also be shared with two other somatic conditions for which ADHD patients are at increased risk: obesity and eczema. It is possible that common inflammatory processes account for this overlap among disorders. Clinicians should be aware that children with asthma have an increased risk for ADHD, although given the small association, systematic screening may not be warranted. But given that ADHD might interfere with asthma medication compliance, the disorder should be considered among noncompliant youth, especially those who show other evidence of inattention, poor memory or disorganization.
Samuele Cortese, Shihua Sun, Junhua Zhang, Esha Sharma, Zheng Chang, Ralf Kuja-Halkola, Catarina Almqvist, Henrik Larsson, Stephen V Faraone, “Association between attention deficit hyperactivity disorder and asthma: a systematic review and meta-analysis and a Swedish population-based study,” Lancet Psychiatry, Published online July 24, 2018.