Residential trees and allergic outcomes
Other studies on trees and allergic outcomes did not observe an association with AR. 35,36 This contrasts with our analysis where this association was the strongest and the most consistent. Yet, Lovasi et al. 36 reported increased risks of asthma and allergic sensitization in 549 7-year-old residents of New York, which was partially in line with us. Both studies used tree cover extracted from aerial images. Tree cover does not capture differences between trees.
We used data from a tree registry to distinguish between allergenic and non-allergenic trees. Our results for AR and to a lesser extent for aeroallergen sensitization suggest that in Leipzig having any trees close to home has about the same negative health effect as having allergenic trees close by. This might not be the case for other study areas. Future research might show that comparisons of findings concerning trees and allergic outcomes are only valid between cities with similar tree patterns, air quality and urban climate.37
No epidemiological study so far had enough information to adequately deal with the problem that pollen loads as well as allergenic potentials may vary between tree individuals and for the same tree individuum, also across years. 38 For most allergenic tree species this phenomenon has not yet been explored let alone been understood.