Relation between asthma and sleep disordered breathing in children: is the association causal?

Over the last few decades, asthma and sleep disordered breathing (SDB) in children have experienced similar increases in prevalence, and have both been shown to have airway inflammation, leading investigators to postulate an association between asthma and SDB. However, whether this relationship is causal or not needs to be proven. In this manuscript, we use the most widely accepted epidemiologic criteria for causality, the Bradford Hill criteria, to test step-by-step whether the relation between asthma and SBD in children is causal or not. We found studies supporting 8 of the 9 criteria (strength, consistency, specificity, biological gradient, coherence and biological plausibility, experiment, and analogy) for association between asthma and SDB. However, we did not find any study showing temporality or directionality between asthma and SDB. Therefore, establishing a causal association between asthma and SDB is not yet possible.