Residential greenness is associated with peripheral blood leukocyte profiles and lower odds of hospital admission in children with asthma: a retrospective observational study

Background Asthma is a common chronic respiratory disease in children and is influenced by environmental factors such as air pollution and urbanization. Often quantified using the Normalized Difference Vegetation Index (NDVI), residential greenness has emerged as a potential beneficial factor through mechanisms such as pollution reduction and immune modulation. However, its relationship with clinical severity and inflammatory responses in pediatric asthma remains unclear. Methods This retrospective observational study included 4,688 pediatric patients (< 16 years) presenting with asthma exacerbations to the emergency department of a tertiary medical center in Kaohsiung between 2007 and 2018. Residential greenness was assessed using NDVI at a 1-km resolution. Air pollutant and meteorological data were obtained from local monitoring stations. Clinical data, laboratory parameters (white blood cell count, neutrophils, lymphocytes, eosinophils), and outcomes (hospital admission, intensive care unit (ICU) admission) were collected. Multivariable and logistic regression analyses were performed adjusting for confounders, including age, sex, and environmental factors. Results Higher residential greenness was significantly associated with lower levels of air pollutants, including PM 2.5 , PM 10 , NO₂, and SO₂. Greenness was positively associated with lymphocyte counts (10/µL, β = 485.936, p = 0.029) and lymphocyte percentage (β = 5.522, p = 0.007), and negatively associated with neutrophil percentage (β = −9.179, p = 0.024), thus indicating a shift toward a less inflammatory peripheral blood leukocyte profile. Clinically, greenness was significantly associated with lower pulse rate (β = −6.05 pulse per minute, p = 0.032). Importantly, higher greenness was associated with reduced odds of hospital admission (OR = 0.578, 95%CI = 0.335–0.999, p = 0.05), with borderline associated with ICU admission (OR = 0.208, 95%CI = 0.035–1.223, p = 0.082). Conclusions Our results suggested that residential greenness was associated with differences in peripheral blood leukocyte profiles, improved physiological parameters, and reduced hospitalization risk in pediatric patients with asthma. These findings support the potential association between green environments in reducing asthma severity and improving clinical outcomes. Further studies are needed to clarify underlying biological mechanisms.