Urban Tree Canopy and Asthma, Wheeze, Rhinitis, and Allergic Sensitization to Tree Pollen in a New York City Birth Cohort

Article excerpt

BACKGROUND: Urban landscape elements, particularly trees, have the potential to affect airflow, air quality, and production of aeroallergens. Several large-scale urban tree planting projects have sought to promote respiratory health, yet evidence linking tree cover to human health is limited.

OBJECTIVES: We sought to investigate the association of tree canopy cover with subsequent development of childhood asthma, wheeze, rhinitis, and allergic sensitization.

METHODS: Birth cohort study data were linked to detailed geographic information systems data characterizing 2001 tree canopy coverage based on LiDAR (light detection and ranging) and multispectral imagery within 0.25 km of the prenatal address. A total of 549 Dominican or African-American children born in 1998-2006 had outcome data assessed by validated questionnaire or based on IgE antibody response to specific allergens, including a tree pollen mix.

RESULTS: Tree canopy coverage did not significantly predict outcomes at 5 years of age, but was positively associated with asthma and allergic sensitization at 7 years. Adjusted risk ratios (RRs) per standard deviation of tree canopy coverage were 1.17 for asthma (95% CI: 1.02, 1.33), 1.20 for any specific allergic sensitization (95% CI: 1.05, 1.37), and 1.43 for tree pollen allergic sensitization (95% CI: 1.19, 1.72).

CONCLUSIONS: Results did not support the hypothesized protective association of urban tree canopy coverage with asthma or allergy-related outcomes. Tree canopy cover near the prenatal address was associated with higher prevalence of allergic sensitization to tree pollen. Information was not available on sensitization to specific tree species or individual pollen exposures, and results may not be generalizable to other populations or geographic areas.

KEY WORDS: aeroallergen, allergic sensitivity, asthma, built environment, childhood disease, environmental agents, epidemiology, pollen, urban life. Environ Health Perspect 121:494-500 (2013). http://dx.doi.org/10.1289/ehp.1205513 [Online 15 January 2013]

In the United States, a disproportionate burden of severe childhood asthma affects families in poverty, racial or ethnic minorities, and innercity communities (Akinbami and Schoendorf 2002; Busse and Mitchell 2007; Grant et al. 2000; Matricardi et al. 2002). Recent evidence points to intraurban variability in exposure to air pollution (Carlsten et al. 2011; Padhi and Padhy 2008), allergens (Olmedo et al. 2011), environmental tobacco exposure (Cook and Strachan 1999; Gilliland et al. 2001; Larsson et al. 2001), lifestyles (e.g., sedentary behavior, diet, obesity) (Eder et al. 2006; Platts-Mills et al. 2006; Yang et al. 2007), and aspects of the social environment (Chen et al. 2008; Clougherty et al. 2007; Kilpellainen et al. 2002) that may affect the incidence of asthma or allergic sensitization, a key asthma risk factor (Illi et al. 2006; Porsbjerg et al. 2006; Tuchsen and Hannerz 2000).

Urban landscape elements, particularly trees, have the potential to affect air flow, air quality, and the production of aeroallergens (Bealey et al. 2007; Escobedo et al. 2008; McPherson et al. 1997; Pincus and Stern 1937; Tallis et al. 2011). Air quality and respiratory health improvements are among the anticipated economic and social benefits of the urban forest (Bloomberg 2007; Nowak 2007). Trees may cause small reductions in particulate matter and ozone concentrations (Escobedo et al. 2008; McPherson et al. 1997; Nowak et al. 2000), though evidence directly linking trees to neighborhood air quality is limited. However, one study reported that more vegetation within a 100-m or 250-m buffer around the home was associated with lower personal exposure to particulate matter [less than or equal to] 2.5 [mu]m (P[M.sub.2.5]) (Dadvand et al. 2012). Some tree species also produce allergens, which may trigger seasonal allergic rhinoconjunctivitis or asthma exacerbations in sensitized individuals (Dales et al. …