Green spaces have benefits but may also increase the risk of allergic disease. This study examined the association between the first occurrence of asthma and greenness exposure in children and teenagers. We conducted a 1:1 matched case-control study matched by sex, age, and the first diagnosis year with 7040 eligible subjects from a systematic sampling cohort database in Taiwan from 2001 to 2013. A normalized difference vegetation index (NDVI) value ≥0.4 was used as the criterion to determine the green space. The green cover images were then transformed to the green coverage rate in the township surrounding the residential areas of the asthma and control subjects. Conditional logistic regression analyses demonstrated that a significantly increased risk of asthma in preschool children was associated with the surrounding greenness after adjusting for urbanization level, frequency of healthcare provider visits, mean township family income, CO, NOx, and PM2.5. The risk of asthma occurrence increased significantly with increasing greenness exposure (p-trend < 0.05). Nevertheless, exposure to the highest greenness levels (81-100%) was not associated with a significantly higher risk of asthma occurrence than was exposure to the lowest values (0-20%) of greenness. This study suggests that green space design should consider more effective methods of reducing the allergy impact.
Keywords: air pollution; asthma; greenness space; preschool children.