Greenness exposure: beneficial but multidimensional

Many studies have shown that greenness has beneficial health effects, particularly on psychological and cardiovascular outcomes. In this narrative review, we provide a synthesis of knowledge regarding greenness exposure and respiratory health. The following outcomes were reviewed: respiratory mortality, lung cancer mortality, lung cancer incidence, respiratory hospitalisations, lung function, COPD, and asthma. We identified 174 articles through a literature search in PubMed, of which 42 were eligible for inclusion in this review. The most common marker for greenness exposure was the normalised difference vegetation index (NDVI), which was used in 29 out of 42 papers. Other markers used were tree canopy cover, landcover/land-use, plant diversity, density of tall trees and subjectively perceived greenness. We found beneficial effects of greenness in most studies regarding respiratory mortality, lung cancer incidence, respiratory hospitalisations and lung function. For lung cancer mortality, asthma and COPD, the effects of greenness were less clear cut. While many aspects of greenness are beneficial, some aspects may be harmful, and greenness may have different health effects in different population subgroups. Future studies of greenness and respiratory diseases should focus on asthma and COPD, on effects in different population subgroups and on disentangling the health effects of the various greenness dimensions.