Allergy

Residential greenness is differentially associated with childhood allergic rhinitis and aeroallergen sensitisation in 7 birth cohorts

Fuertes E, Markevych I, Bowatte G, Gruzieva O, Gehring U, Becker A, Berdel D, von Berg A, Bergström A, Brauer M, Brunekreef B, Brüske I, Carlsten C, Chan-Yeung M, Dharmage SC, Hoffmann B, Klümper C, Koppelman GH, Kozyrskyj A, Korek M, Kull I, Lodge C, Lowe A, MacIntyre E, Pershagen G, Standl M, Sugiri D, Wijga A, Heinrich J. Allergy 2016; Epub 18 April 2016

Inconsistent evidence for the effect of residential greenness on allergic outcomes

Whilst the beneficial effect of surrounding greenness has been demonstrated for several health measures, its effect on allergic outcomes is unclear.1 The role of residential greenness on the prevalence of allergic rhinitis and sensitisation was investigated in a recent analysis of individual data from seven birth cohort studies from Sweden, Australia, The Netherlands, Canada and Germany. 1

The study, published in Allergy, looked at the prevalence of allergic rhinitis and sensitisation to aeroallergens during childhood (6–8 years of age; six cohorts) and early adolescence (10–12 years of age; five cohorts). 1

The study designs and definitions differed between the studies. Allergic rhinitis was defined by either: 1

• Physician assessment
  
• Parental report of physician diagnosis
  
• Or parental report of symptoms or treatment

Sensitisation to outdoor and indoor allergens was assessed by either: 1

• Skin prick testing
  
• Or measurement of specific immunoglobulin E levels.

The mean Normalised Difference Vegetation Index (NDVI), an indicator of green biomass density, was used to measure the residential greenness in a 500 m buffer surrounding each participants’ home. 1

Interactions with nitrogen dioxide (NO2) concentrations, a rural/urban indicator and population density were also tested. 1

In total, information on NDVI and at least one outcome of interest was available for 13,016 children, with individual cohort sizes ranging from 327 to 3,339 children. 1

Study outcomes

The associations of mean NDVI in a 500 m buffer with allergic rhinitis and aeroallergen sensitisation were different in the seven birth cohorts, and the overall combined finding was non-significant. 1

Logistic regression analysis revealed several cohorts had a positive association between increased greenness in the 500 m buffer and allergic rhinitis at age 6–8: the Swedish (odds ratio [OR] 1.42, 95% confidence interval [CI] 1.13–1.79) and urban German (OR 1.69, 95% CI 1.19–2.41) cohorts.

However, the inverse relationship was found in other cohorts (rural German [OR 0.61, 95% CI 0.36–1.01] and Dutch [OR 0.67, 95% CI 0.47–0.95] cohorts). 1

For each cohort, the association with allergic sensitisation was similar to that with allergic rhinitis. 1

Studies in early adolescence yielded similar results; the Australian study (which only had data for the 10–12 year age group), showed an inverse association between greenness and allergic sensitisation (OR 0.57, 95% CI 0.34–0.96) whilst the relationship with allergic rhinitis was non-significant (OR 0.96, 95% CI 0.59–1.57). 1

Including effect modifiers such as gender, NO2 exposure, population density and an urban/rural marker did not clarify the results. 1

Conclusions

In all, there was regional variability in the direction of the association between mean NDVI in a 500 m buffer and allergic rhinitis and sensitisation. 1 This could have several explanations; for example, the use of NDVI may only have local interpretations, or there may be unknown confounding factors which are region-specific. 1

However, the authors hypothesised that the most important outcome from this study may pertain to the use of NDVI in allergic health research.1 The NDVI may be too general a measure, and does not capture sufficient information on vegetation types with respect to pollen exposure and duration of exposure.1 The authors recommended that future studies on allergic diseases and the role of the residential greenness should include more detailed data on tree and herbaceous species. 1

Report on: Residential greenness is differentially associated with childhood allergic rhinitis and aeroallergen sensitization in seven birth cohorts. Fuertes E, Markevych I, Bowatte G, Gruzieva O, Gehring U, Becker A, Berdel D, von Berg A, Bergström A, Brauer M, Brunekreef B, Brüske I, Carlsten C, Chan-Yeung M, Dharmage SC, Hoffmann B, Klümper C, Koppelman GH, Kozyrskyj A, Korek M, Kull I, Lodge C, Lowe A, MacIntyre E, Pershagen G, Standl M, Sugiri D, Wijga A, Heinrich J. Allergy 2016; Epub 18 April 2016.

Reference list

1. Fuertes E, Markevych I, Bowatte G, Gruzieva O, Gehring U, Becker A, et al. Residential greenness is differentially associated with childhood allergic rhinitis and aeroallergen sensitization in seven birth cohorts. To be published in Allergy. [Preprint] 2016.