The associations between residential greenness and allergic diseases in Chinese toddlers: A birth cohort study

Green space in the living environment has been linked to the development of allergic diseases. However, evidence regarding early-onset allergy in toddlers was limited, and the critical exposure window remained unclear. We aimed to investigate associations between residential greenness with allergic diseases in early life. This prospective birth cohort study included 522 mother-child pairs in Guangzhou, China. We quantified prenatal, postnatal, and early-life (i.e., the first 1000 days of life) residential greenness, estimated from remote satellite data using normalized difference vegetation index (NDVI), enhanced vegetation index (EVI), and tree cover. We identified physician-diagnosed allergic diseases (eczema, atopic dermatitis, urticaria, allergic rhinitis, allergic conjunctivitis, food allergy, and asthma) based on medical records at age 2 years. Generalized linear regression was conducted to examine the associations of greenness with allergic outcomes. The ranges of residential NDVI and EVI values in 500-m buffer during early life were 0.06–0.70 and 0.03–0.46, respectively. We found a 0.1 unit increase of NDVI in 500-m buffer throughout early life was associated with higher odds of any allergic diseases (prenatal: OR [odds ratio], 1.25; 95%CI, 1.02–1.53; postnatal: OR, 1.24; 95%CI, 1.02–1.52; early-life: OR, 1.25, 95%CI: 1.02–1.53) and higher odds of eczema (prenatal: OR, 1.28; 95%CI, 1.04–1.59; postnatal: OR, 1.24; 95%CI, 1.01–1.54; early-life: OR, 1.26, 95%CI: 1.02–1.56). The results were consistent when using EVI as a proxy for greenness. We only observed that prenatal exposure to the highest tertile of NDVI-500 was adversely associated with any allergic diseases (OR, 1.63; 95%CI, 1.03–2.58) and eczema (OR, 1.70; 95%CI: 1.04–2.78) compared with the lowest tertile. This study identified detrimental associations of residential greenness with allergic diseases especially eczema among toddlers, and pregnancy appears to be the critical exposure window. Our findings highlighted the importance of urban planning to develop friendly-green neighborhood to improve maternal and child health.