Residential greenness and allergic respiratory diseases in children and adolescents – A systematic review and meta-analysis

Background The aetiology of allergic respiratory disease in children is not yet fully understood. Environmental factors are believed to play a major part. The amount of green vegetation surrounding the home (residential greenness) has been recently identified as a potentially important exposure Objectives Our goal was to provide a systematic review and quantitative summary of the evidence regarding the relationship between residential greenness and allergic respiratory diseases in children. Methods Peer-reviewed literature published prior to 1 March 2017 was systematically searched using nine electronic databases. Meta-analyses were conducted if at least three studies published risk estimates for the same outcome and exposure measures. Results We included 11 articles across broad outcomes of asthma and allergic rhinitis. Reported effects were inconsistent with varying measures to define residential greenness. Only limited meta-analysis could be conducted, with the pooled odds ratios for asthma (OR 1.01 95%CI 0.93, 1.09; I² 68.1%) and allergic rhinitis (OR 0.99 95%CI 0.87, 1.12; I² 72.9%) being significantly heterogeneous. Conclusions Inconsistencies between the studies were too large to accurately assess the association between residential greenness and allergic respiratory disease. A standardised global measure of greenness which accounts for seasonal variation at a specific relevant buffer size is needed to create a more cohesive body of evidence and for future examination of the effect of residential greenness on allergic respiratory diseases.