Conclusions
Our findings provide new evidence that early-life exposure to green spaces, measured as NDVI, during the spring increases the risk of developing allergic rhinitis in childhood. In contrast, during the summer, similar exposure reduces the risk of allergic rhinitis. The important bi-directional role of the season in the effects of exposure to green spaces on allergic rhinitis is likely to be explained by qualitative and quantitative changes in vegetation over the seasons. This may also explain the previous inconsistent results on the association between the exposure to green spaces and the risk of allergic rhinitis. Our finding of effect modification of the relation between green spaces and allergic rhinitis by air pollution levels suggests that provision of green spaces in urban areas can be considered as a complementary preventive measure against adverse effects of air pollution.
Table 1 Characteristics of the baseline study population (n = 2568), The Espoo Cohort Study 1983-2011