Exposure to green spaces is expected to have positive health effects, but often means higher exposure to pollens and moulds, which have been shown to increase respiratory symptoms in children in both the short and long term. On the other hand, trees can decrease air pollution levels, which are also adversely associated with respiratory symptoms.
To further our understanding of the balance between pollen and air pollution, we analyzed the association between respiratory symptoms in children aged 3-14 years and the percentage of green spaces within 500 m of their residence.
Data from 7,727 children, aged 3-14, were obtained from six population-based studies participating in the HEALS consortium. Land-cover estimates within a 500 m buffer centred on each child’s residential address were computed using the Coordination of Information on the Environment (CORINE) programme. The associations between green space coverage and respiratory symptoms (lifetime and current wheeze, lifetime and current asthma, and allergic rhinitis) were estimated for each survey using logistic regression models, adjusted for sex, age, body mass index, maternal education, exposure to passive smoking, and parental history of allergy. Finally, the pooled effects across studies were estimated using inverse-variance method meta-analyses.
In the pooled analyses, an increase of 10% in green space was significantly associated with greater risks of lifetime wheeze (OR=1.058, p=0.027), current wheeze (OR=1.131, p=0.001) and allergic rhinitis (OR=1.087, p=0.020). In secondary analyses, the presence of coniferous forests near the residence was significantly associated with increased risk of wheezing (OR=1.720, p=0.043), current wheezing (OR= 3.600, p<0.001), current asthma (OR= 1.427, p=0.005) and allergic rhinitis (OR= 3.254, p<0.001).
Preliminary results show an increased risk between some respiratory symptoms and the percentage of green space within 500 m in children aged 3 to 14 years. Further analyses will concentrate on other land features, including grey space (urban areas) and agricultural spaces at multiple radii, and on seasonality and concomitant exposure to air pollution in order to better clarify these associations.