Residential green space types, allergy symptoms and mental health in a cohort of tree pollen allergy patients

Background: Exposure to green space has been associated with positive mental and physical health outcomes. Nevertheless, green space can also act as a source of aeroallergens and exacerbate allergic disease and related mental distress. We examined impacts of exposure to residential green space on respiratory health and well-being in a cohort of adults sensitized to tree pollen allergens. Methods: In a panel of 157 tree pollen allergy patients in Belgium we analyzed average allergy symptom scores, average mood scores, distress (GHQ-12) and perceived stress (PSS). Generalized linear models were used to investigate associations between health outcomes and garden cover, grassland cover, forest cover and density of trees of the allergenic Alnus, Betula and Corylus genera in forests within a 1, 2 and 5 km distance from the residence. Models were adjusted for sex, age, BMI, allergy medication use, chronic respiratory disease, smoking behavior, education level, physical activity and perceived presence of allergenic trees. Results: We observed inverse associations between residential garden cover within 1 km distance and perceived stress (PSS) (unadjusted beta = -0.020; 95% CI [-0.031; -0.008]) and between forest cover within 1 km and distress (GHQ-12) (-0.048 [-0.085; -0.011]). Higher densities of allergenic trees in forests within 2 km distance were associated with higher PSS (0.003 [0.000 - 0.006]) and GHQ-12 scores (0.020 [0.014; 0.027]). Residential green space variables within 1 km distance were associated with higher symptom scores: garden cover beta = 0.013 [0.007; 0.018], grassland cover beta = 0.020 [0.014; 0.026], forest cover beta = 0.016 [0.010; 0.021], density of allergenic trees in forests beta = 0.005 [0.001; 0.009]. The parameter estimates became smaller at larger scales and remained significant in the fully adjusted models. Conclusion: Green space is associated with more symptoms but lower distress and allergenic trees in forests are associated with higher distress Residential green space has mixed health effects in tree pollen allergy patients.