Normalised difference vegetation index and allergies among four-year-old children living in the greater Tokyo area, Japan: Findings from an Adjunct Study of the Japan Environment and Children's study

This study investigated the association between residential greenness exposure and the prevalence of allergic diseases in four-year-old children in the Greater Tokyo Area, Japan. It was an Adjunct Study of the Japan Environment and Children's Study, an ongoing nationwide birth cohort study. Participants who resided in the Greater Tokyo Area at both three and four years of age were selected and 10,846 children were included in the analysis. Residential greenness was defined as the average normalised difference vegetation index (NDVI) within a 500 m buffer of each home, derived from Landsat satellite images. Guardians reported their children's allergy status based on a doctor's diagnosis and the International Study of Asthma and Allergies in Childhood (ISAAC). Multiple logistic regression analysis examined the association between residential NDVI and allergic outcomes, adjusting for child characteristics, maternal factors, socioeconomic indicators, and indoor environmental exposures as potential confounders. The average (standard deviation) NDVI was 0.15 (0.05). For atopic dermatitis, the adjusted odds ratios (95%CI) were 0.84 (0.72-0.97) for physician diagnosis (guardian-reported) and 0.82 (0.72-0.94) for ISAAC. For asthma, the corresponding odds ratios were 1.25 (1.10-1.42) and 1.25 (1.11-1.40). No association with NDVI was observed for any other allergies. These results were consistent regardless of the buffer size. The observed negative associations between greenness and atopic dermatitis are compatible with the biodiversity hypothesis. The positive associations between greenness and childhood asthma warrant further examination, specifically regarding the quality and composition of greenness and air quality. These findings are crucial for developing effective public health guidelines.