Residential greenness and atopic dermatitis in Japanese children: Findings from the TMM BirThree cohort study

BACKGROUND: Atopic dermatitis (AD) is a chronic inflammatory skin disease that primarily develops during childhood. Residential greenness has been reported to be associated with AD onset. However, findings are inconsistent and may not apply to Japanese settings because vegetation and residential environments vary regionally. Therefore, this study aimed to examine early-life exposure to residential greenness and subsequent AD development in Japanese children. METHODS: We analyzed data from 14,932 children in the Tohoku Medical Megabank Project Birth and Three-Generation Cohort Study. The exposure was residential greenness during the first 6 months of life, quantified using the normalized difference vegetation index (NDVI) within 250-, 500-, and 1000-m buffers around each birth postal code and categorized into tertiles (low [reference], moderate, high). The outcome was AD incidence between 6 months and 5 years of age, assessed via maternal reporting. Adjusted risk ratios (RRs) and 95% confidence intervals (CIs) were estimated using modified Poisson regression. Analyses were stratified by urbanization levels, child's sex, and parental history of allergic diseases. RESULTS: A significant protective association was observed among children in the high NDVI tertile within the 250-m buffer (adjusted RR: 0.80, 95% CI: 0.67-0.95), whereas the moderate tertile was not significant (adjusted RR: 0.94, 95% CI: 0.83-1.06). A similar pattern was observed at 500 m. Stratification showed similar associations across urbanization levels, which were stronger in boys and observed only among children without parental allergic history. CONCLUSION: Early-life exposure to residential greenness was associated with a decreased risk of AD in Japanese children.