• Asthma Epidemiology

In Thorax, Campbell et al1 report an association of growing up on a farm with better adult lung function. On closer investigation, this effect was confined to the FEV₁ in female participants in the study. A novel finding and a paper worth reading—but what may be harder to glean is its relevance and implication for future research.

The ‘farm-effect’ on allergic disease has been well established in numerous studies. Recent systematic reviews with meta-analyses show a strong protective effect of growing up on a farm on childhood atopy2 and a lesser effect on childhood asthma.3 In these meta-analyses, the effect estimates for the ‘farm-effect’ on asthma were much more heterogeneous than those on any atopic sensitisation.2 ,3 This may be driven by the mix of different farm exposures shown to be important.4 It has also been suggested that the increased heterogeneity in estimates of the ‘farm-effect’ on asthma is partly driven by the mix of asthma phenotypes in the respective studies.3

Indeed, the present study by Campbell et al is one of the few studies presenting results completely stratified by atopy to investigate this further. Here, the authors conclude that protective effects on atopic asthma, atopic bronchial hyper-responsiveness (BHR) and atopic nasal symptoms in comparison to non-atopic subjects without asthma, BHR and nasal symptoms, respectively, exist. On closer investigation of the presented data, these associations are fully driven by the ‘farm effect’ on atopy. No separate ‘farm-effect’ on asthma, BHR or nasal symptoms shows …