Neighbourhood green and blue spaces and allergic sensitization in children: A longitudinal study based on repeated measures from the Generation XXI cohort
Inês Paciência a,⁎, André Moreira a,b,c,d, Carla Moreira e, João Cavaleiro Rufo a,b, Oksana Sokhatska c, Tiago Rama c,d, Elaine Hoffimann a, Ana Cristina Santos a,b, Henrique Barros a,b, Ana Isabel Ribeiro a,b
aEPIUnit, Instituto de Saúde Pública da Universidade do Porto, Rua das Taipas 135, 4050-600 Porto, Portugal
bFaculdade de Medicina da Universidade do Porto, Al. Prof. Hernâni Monteiro, 4200-319 Porto, Portugal
cServiço de Imunologia Básica e Clínica, Departamento de Patologia, Faculdade de Medicina da Universidade do Porto, Al. Prof. Hernâni Monteiro, 4200-319 Porto, Portugal
dServiço de Imunoalergologia, Centro Hospitalar Universitário de São João, Al. Prof. Hernâni Monteiro, 4200-319 Porto, Portugal
eCmat – Centre of Mathematics School of Sciences, University of Minho, Campus de Gualtar, 4710-057 Braga, Portugal
H I G H L I G H T S
•Exposure to green space (NDVI) was as- sociated with a lower risk of allergic sensitization.
•Cumulative and late-childhood expo- sures to green space had a bigger im- pact.
•There was no association between the exposure to blue spaces and allergic sensitization.
•The provision of green spaces in urban environments may promote children health.
G R A P H I C A L A B S T R A C T
a r t i c l e i n f o a b s t r a c t
Article history:
Received 27 October 2020
Received in revised form 19 January 2021 Accepted 19 January 2021
Available online 27 January 2021 Editor: Elena Paoletti
Keywords: Allergy Childhood Environment Greenness Urban areas
Evidence on the effect of natural environments on atopy in children is limited and inconsistent, disregarding the time-varying and cumulative exposures throughout the life course. To assess critical periods of exposure as well as the effect of longitudinal trajectories of exposure to green and blue spaces on the development of allergic sen- sitization in children at the age of 10 years. A longitudinal study was conducted involving 730 children enrolled in Generation XXI, a population-based birth cohort from the Porto Metropolitan Area (Portugal). Food and aeroallergens sensitization were evaluated at 10 years of age using Phadiatop Infant, Phadiatop fx1 and fx22 ImmunoCAP (Thermo Fisher Scientific, Uppsala, Sweden). Residential Normalized Difference Vegetation Index (NDVI) and distance to the nearest blue space (sea, river) were assessed using a Geographic Information System. Latent class linear mixed models were fi tted to determine longitudinal trajectories of exposure. Associations were estimated using Cox proportional hazards regression models and expressed using hazard ratios (HR) and 95% confidence intervals (95% CI). Residing in neighbourhoods surrounded by more vegetation at 10 years, as well as lifetime exposure to a trajectory of higher levels of NDVI, were associated with a lower risk of allergic sen- sitization [HR (95% CI) = 0.095 (0.011, 0.823) and HR (95% CI) = 0.539 (0.301, 0.965), respectively]. Our findings support a role for both longitudinal, but particularly late-childhood, exposure to green spaces, in the prevention of allergic sensitization in children.
© 2021 Elsevier B.V. All rights reserved.
⁎ Corresponding author.
E-mail address: [email protected] (I. Paciência).
https://doi.org/10.1016/j.scitotenv.2021.145394 0048-9697/© 2021 Elsevier B.V. All rights reserved.
1.Introduction
In a world with rapid and growing urbanization, evidence on the health impacts resulting from environmental exposures is increas- ingly relevant. A recent meta-analysis suggests that access and expo- sure to natural environments can signifi cantly infl uence human health, including physical and mental health, as well as wellbeing (Twohig-Bennett and Jones, 2018). Also, they may decrease the effects related to environmental factors, such as air pollution, noise or climate extremes, and consequently reduce the risk of adverse health effects (James et al., 2015). A growing body of evidence sug- gests that early-life exposure to natural environments has several important health effects, namely on the modulation of the immune system and the development of chronic infl ammatory diseases (Ruokolainen et al., 2016; Jackson et al., 2017).
Different pathways have been proposed to explain the health effects of green spaces (Markevych et al., 2017). Indeed early-life exposure to green space has been inversely associated with the development of allergic manifestation in children (Ruokolainen et al., 2015). Green space may affect the composition of the human microbiota, which in turn may refl ect immunologic responses to en- vironmental diversity and protect against chronic infl ammatory dis- orders, including allergic diseases (Hanski et al., 2012). These fi ndings are consistent with the “biodiversity hypothesis” (von Hertzen et al., 2011), which proposes that people’s reduced contact with natural environments and biodiversity leads to an inappropri- ate infl ammatory response. Additionally, green spaces can act as a buffer against exposure to air pollution, by removing pollutants from the atmosphere or limiting dispersion towards sidewalks where people are often exposed to pollutant emissions (Nowak et al., 2006; Selmi et al., 2016), thereby reducing some of the envi- ronmental risks associated with urban life.
Epidemiological studies on the infl uence of natural environments on atopy among children are limited and inconsistent (Dadvand et al., 2014; Ruokolainen et al., 2015; Fuertes et al., 2016; Cavaleiro Rufo et al., 2019; Gernes et al., 2019). These contradicting results may refl ect the differences in the defi nition of green space and in terms of the quality and/or accessibility of green spaces but also differences in the study design, ascertainment of the outcome and timing of exposure (Shin et al., 2017; Ferrante et al., 2020). Additionally, most of the previous studies assessed the effect of green space at a single point in time, disregarding the time-varying cumulative exposure, or the associations at specifi c time points over the life course. Therefore, a life-course approach can contribute simultaneously to understanding the effect of cumulative exposures to natural environments or whether there are critical periods during the life course that are particularly important for a higher risk of atopy among children (Halfon and Hochstein, 2002). Furthermore, a growing body of evidence suggests that living near blue space (seas or other water bodies) leads to positive effects on physical and mental health (White et al., 2016; Gascon et al., 2017). Blue space has been associated with lower levels of environmental hazards, including air pollutants and noise, and increased physical activity and social cohesion (Markevych et al., 2017). Considering that some of the proposed pathways (air pollution and physical activity) for the associations between blue space and health are sim- ilar to those for green space, exposure to blue space may also have a benefi cial impact on allergic sensitization in children. However, to the best of our knowledge, this potential association has not yet been explored. Our hypothesis is that exposure to residential green and blue spaces in childhood may be associated with a lower risk of allergic sensitization at 10 years of age. Therefore, this longitudinal study aims to assess critical periods of exposure to residential green and blue spaces during children’s life course on the develop- ment of allergic sensitization in children at the age of 10 years. Addi- tionally, this study also aims to assess the effect of longitudinal
trajectories of exposure to green and blue spaces on allergic sensitization.
2.Methods
2.1.Study participants
The study used data collected from the Generation XXI (G21) birth cohort, which includes 8495 mothers and 8647 new-borns delivered in 2005 and 2006 in the Porto Metropolitan Area in Northern Portugal. The initial recruitment took place between April 2005 and September 2006 at all five public maternity units, where 95% of the region’s births occur. During the hospital stay, women delivering live births with more than 23 gestational weeks were invited to participate in the G21 cohort study, and 92% of the mothers agreed. Information on demographic and socioeconomic characteristics, lifestyles, obstetric history, anthropo- metrics, and personal history of disease were collected within 72 h after delivery by a face-to-face interview using a standardized question- naire (Alves et al., 2012) (questionnaire provided in Appendix A in Suppl. Mat.). All participants were invited to be re-evaluated at four (2009/11), seven (2012/14) and 10 (2015/17) years of age. More details regarding the cohort have been previously published (Larsen et al., 2013). Ethical approval for the study was obtained from the Ethics Com- mittee of the University Hospital Center of São João (CES-01/2017) and signed informed consent was obtained from all participant’s caregivers. All phases of the study followed the Ethical Principles for Medical Re- search Involving Human Subjects expressed in the Declaration of Helsinki.
Child’s residential address was collected during routine telephone calls with the caregiver at the time of each evaluation, processed and georeferenced using ArcGIS Online World Geocoding Service and Goo- gle Earth, due to their superior positional accuracy (Ribeiro et al., 2014). Address georeferencing enables the linkage of environmental ex- posures to participants across different timepoints.
During the evaluations, participants were subjected to a physical ex- amination by trained personnel. Following an overnight fast, a venous blood sample was drawn, centrifuged at 3500 rpm for 10 min, aliquoted, analysed, or deep frozen (-80 °C) until analysis. Among the 4047 par- ticipants with blood samples collected at 10 years of age, 800 partici- pants were randomly selected and screened with Phadiatop. For the current study, a subsample of children who lived in the Porto Metropol- itan Area since birth and with data on Phadiatop test results were in- cluded for a total of 730 children.
2.2.Food and aeroallergens allergic sensitization
Serum samples collected from children at 10 years of age were tested for specific IgE antibodies using ImmunoCAP fx1 nut mix (pea- nut, hazel nut, Brazil nut, almond and coconut), fx22 nut mix (pecan nut, cashew nut, pistachio and walnut) and Phadiatop Infant (hen’s egg, cow’s milk, peanut, shrimp, cat epithelium and dander, dog dander, house dust mite, common silver birch, timothy, ragweed, and wall pel- litory) (Thermo Fisher Scientific, Uppsala, Sweden). Allergic sensitiza- tion was defi ned as a result equal to or higher than 0.35 kU/L according to the manufacturer’s instructions for at least one of the tested aeroallergens or food allergens.
2.3.Exposure assessment
2.3.1.Green space
Green space was assessed using the mean Normalized Difference Vegetation Index (NDVI) within 100 m, 250 m and 500 m of the child’s residence at birth, four, seven and 10 years of age. These buffer sizes were selected to cover immediate and more distant areas of exposure, and have been employed elsewhere (Dadvand et al., 2012; Eldeirawi et al., 2019). The calculation of the NDVI was
based on land surface refl ectance of visible red (VISR) and near- infrared (NIR) wavelengths, using the following equation (Eq. (1)):
2.4.3.Distance to the nearest major road, motorway or highway
The distance from children’s houses to the nearest major road, mo- torway or highway was calculated using ArcMap 10.5.1 based on a
NDVI ¼
NIR-VISR NIR þ VISR
ð1Þ
street network dataset obtained from HERE®, which was provided by courtesy of the Environmental Systems Research Institute (ESRI).
2.4.4.Neighbourhood socioeconomic deprivation
The underlying principle employed in the NDVI calculation is that chlorophyll in healthy vegetation absorb radiation in the visible red re- gion (630–690 nm) of the electromagnetic spectrum and reflect radia- tion in the near-infrared region (760–900 nm) (Weier and Herring, 2000). The values range from -1 (water) through zero (rock, sand and snow) to 1, with higher positive values indicating denser green veg- etation (i.e. photosynthetically active and healthy vegetation). As in previous investigations from the G21 cohort (Ribeiro et al., 2019; Cavaleiro Rufo et al., 2020a), only images with 5% or less cloud coverage from Landsat 5 and 8 (spatial resolution: 30 m) during the spring/sum- mer period (peak of vegetation) of the assessment years (2005/6, 2009/
11, 2012/14 and 2015/17) were used.
The average NDVI was calculated to represent exposure to residen- tial green spaces during the period of the G21 cohort evaluations. Neg- ative NDVI values were not included in the calculation. ArcMap 10.5 was used to process satellite images, and QGIS 3.8 was used to extract the av- erage NDVI within 100 m, 250 m and 500 m of the child’s residence.
2.3.2.Blue space
The Portuguese Water Atlas (from the Portuguese “Atlas da Água”) was used to assess the distance of children’s residence to the nearest blue space, including sea and rivers. The Portuguese Water Atlas was de- veloped by the National Water Resources Information System (SNIRH) under the responsibility of the Portuguese Environment Agency. The SNIRH was created in 1995 and provides information on hydrometeoro- logical variables and water quality (surface, groundwater and coastal) through the network of water resource monitoring stations in Portugal. Residential distance to blue space was calculated as the Euclidean distance from children’s residential address to the nearest river or sea during the period of the G21 cohort evaluations.
2.4.Covariates
A comprehensive set of covariates was selected based on previous studies on associations between allergic sensitization and environmen- tal factors (Nicolai et al., 2003; Baumann et al., 2011; Dadvand et al., 2014; Uphoff et al., 2015; Braubach et al., 2017; Hoffi mann et al., 2017). The following variables were considered: child’s sex, socioeco- nomic conditions measured by maternal educational level and house- hold crowding, and neighbourhood characteristics, more precisely the distance to the nearest major road, motorway or highway and neighbourhood socioeconomic deprivation (Ribeiro et al., 2018).
2.4.1.Maternal educational level
Maternal educational level was measured in years of schooling and categorized into two classes: primary (≤9 years of education, Interna- tional Standard Classifi cation of Education (ISCED) 2011 classes 0–2, corresponding to the compulsory education in Portugal in the age co- hort of the G21 cohort parents), and secondary/tertiary (>9 years, ISCED classes 3–6) (Ribeiro et al., 2020).
2.4.2.Household crowding
Household crowding corresponded to the ratio between the number of household occupants and the number of rooms, and was character- ized as <1.5 or ≥1.5 occupants per room (Fraga et al., 2020). Socioeco- nomic status has been suggested as a risk factor for allergic diseases (Uphoff et al., 2015) and disadvantaged individuals often live in neighbourhoods with reduced availability of green space (Braubach et al., 2017).
As previously described, neighbourhood socioeconomic deprivation was determined based on the weighted sum of the following standard- ized variables obtained from census data: % of non-owned households,
% of households without indoor fl ushing, % of households with ≤5 rooms, % of blue-collar (i.e., manual) occupations, % of residents with low educational level (≤6th grade), % of non-employers, % of unem- ployed individuals looking for a job and % of foreign residents (Ribeiro et al., 2018). The index was categorized into quintiles (the first quintile corresponds to least deprived and the fi fth quintile to the most de- prived). Living in close proximity to a major road and in disadvantaged neighbourhoods have been found to be associated with a lower amount of vegetation and reduced access to green space (Dadvand et al., 2015; Hoffi mann et al., 2017), as well as with a greater risk of allergy (Nicolai et al., 2003; Baumann et al., 2011).
2.5.Statistical analysis
The distribution of continuous variables was analysed for normality. Since non-Gaussian distributions were observed, non-parametric tests were performed for inferential statistics. The Mann-Whitney test was performed to analyse differences between continuous variables and the Chi-square test was used to compare proportions.
Two modelling approaches were used to assess the effect of green and blue spaces on allergic sensitization at 10 years of age: 1) cross- sectional approach; and 2) joint modelling of longitudinal and survival data using the trajectories of residential NDVI and blue space from birth to 10 years of age.
2.5.1.Cross-sectional approach
In the fi rst approach, Cox proportional hazards regression models were fitted to estimate crude and adjusted associations between NDVI and the shortest distance to the nearest blue space at each time point and allergic sensitization at 10 years of age (Fig. 1). The proportional hazard model assumption was examined using the test of scaled Schoenfeld residuals (Grambsch and Therneau, 1994). The results re- vealed no evidence of a violation of the proportional hazards assump- tion (p > 0.05). Both crude (Model 0) and adjusted models (Model 1) were fitted. Model 1 was adjusted for children’s sex, socioeconomic conditions measured by maternal educational level and household crowding, and neighbourhood characteristics, such as the distance to the nearest major road, motorway or highway and neighbourhood so- cioeconomic deprivation.
2.5.2.Joint modelling
In the second approach, the joint model consisted of two sub-models representing the dynamics of longitudinal data (the trajectories of resi- dential NDVI and blue space from birth to 10 years of age) and time-to- event (the survival model) (Proust-Lima et al., 2017). This approach considered the effect of dynamic NDVI and blue space trajectories on al- lergic sensitization. Latent class linear mixed models (LCLMM) were fitted to determine the trajectories of residential NDVI and blue space from birth to 10 years of age (LCLMM) (R Package lcmm) (Proust- Lima et al., 2017). The LCLMM approach, which has been previously employed in investigations on neighbourhood effects (McDonald et al., 2012; Alves et al., 2013), was used to estimate the shape of each NDVI group and distance to blue space over time. The optimal number of trajectory groups was assessed using the Bayesian Information Criteria (BIC) and the posterior probability of belonging to each latent class was also calculated (Suppl. Mat. Tables A.1, A.2, respectively)
Descriptive analysis
1st step
Distribution of continuous variables. Mann- Whitney and Chi-square tests.
Cross-sectional approach
2st step
Cox proportional hazards regression models
To estimate crude and adjusted associations between NDVI and the shortest distance to the nearest blue space at each time point and allergic sensitization at 10 years
Joint modelling
3st step
Latent class linear mixed models (LCLMM)
To estimate the shape of each trajectory group of NDVI and distance to blue spaces over time
The optimal number of trajectory groups was assessed using the Bayesian Information Criteria and the posterior probability of belonging to each latent class was also calculated
Cox proportional hazards regression models
To estimate crude and adjusted associations between the trajectories of NDVI and the shortest distance to the nearest blue space and allergic sensitization at 10 years
Fig. 1. Scheme of statistical analysis.
(Lennon et al., 2018). Then cox proportional hazards regression models were fitted to estimate crude and adjusted associations between the tra- jectories of residential NDVI and blue space and allergic sensitization at 10 years of age (Fig. 1). The proportional hazard model assumption was examined using the test of scaled Schoenfeld residuals (Grambsch and Therneau, 1994). The results revealed no evidence of a violation of the proportional hazards assumption (p > 0.05). Both crude (Model 0) and adjusted models (Model 1) were fitted. Model 1 was adjusted for children’s sex, socioeconomic conditions measured by maternal ed- ucational level and household crowding, and neighbourhood character- istics, such as the distance to the nearest major road, motorway or highway and neighbourhood socioeconomic deprivation.
All covariates were included in the model as categorical variables, except for distance to the nearest major road, motorway or highway, which was included as a continuous variable. There were no moderate or strong correlations between covariates (Suppl. Mat. Table A.3). Re- sults were expressed as the hazard ratio (HR) and the respective 95% confidence interval (95% CI). Effect modification by sex was explored by assessing the statistical signifi cance of multiplicative interactions using likelihood ratio tests by comparing models with and without in- teraction terms. The analyses revealed no significant interaction effects between environmental exposure and sex (Suppl. Mat. Table A.4). Thus, results were presented for the two sexes together. Statistical analysis was performed using R software version 3.6.2.
3.2. Associations with exposures at specific time points
The mean NDVI values within 500 m at four, seven, and 10 years of age were significantly lower among children with allergic sensitization (Table 2). Although no statistically significant differences were found, the mean distance to the nearest blue space was higher among children with allergic sensitization (Table 2). No differences were observed when considering the 100 m and 250 m buffer sizes.
Table 3 shows the crude and adjusted associations between residen- tial exposure to NDVI at specific time points and blue space and allergic sensitization. At 10 years of age, a higher exposure to green space (NDVI) within 500 m of the residence was associated with a lower risk of allergic sensitization [HR (95% CI) = 0.095 (0.011, 0.823)]. Al- though no signifi cant associations between exposure to NDVI earlier in life and allergic sensitization were found, a trend was observed be- tween higher exposure to NDVI and a lower risk of childhood allergic sensitization. No significant associations were observed between dis- tance to the nearest blue space and allergic sensitization at 10 years of age.
Table 1
Characteristics of participants (Generation XXI, n = 730).
Characteristic n (%)
3.Results
At birth
Sex [female]
367 (50.3)
Maternal education
3.1.Participants ≤9 years 327 (44.8)
The study participants’ and exposure characteristics are presented in Table 1. Among the 730 participants included, 367 (50.3%) were female. Forty-four percent of the mothers had a low educational level (≤9 years), and nearly 86% of the children resided in households with a number of occupants per room lower than 1.5. The prevalence of aller- gic sensitization at 10 years of was 39.9%.
The mean [standard deviation (SD)] NDVI increased slightly with in- creasing buffer size [from 0.166 (SD: 0.075) within a 100 m buffer to 0.229 (SD: 0.073) within a 500 m buffer at birth] and overtime [from 0.166 (SD: 0.075) at birth to 0.210 (SD: 0.062) at 10 years of age within a 100 m buffer]; (Fig. 2A). The mean distance to the nearest blue space ranged from 2187.7 (1550.9) m at birth to 2225.8 (1530.5) m at 10 years of age (Fig. 2B).
>9 years
Household crowing (occupants per room)a
<1.5 ≥1.5
Neighbourhood socioeconomic deprivation Q1 (least deprived)
Q2
Q3
Q4
Q5 (most deprived)
Distance to the nearest major road, motorway, or highway (m)b
At 10 years of age Allergic sensitization
an = 707.
bMedian (25th–75th percentile).
403 (55.2) 607 (85.9)
100 (14.1) 146 (20.0)
146 (20.0) 146 (20.0) 146 (20.0) 146 (20.0) 100.2 (38.2–207.1)
291 (39.9)
Fig. 2. Distribution of mean Normalized Difference Vegetation Index (NDVI) within 100 m, 250 m and 500 m of the child's residence (A) and residential distance to the nearest blue space (m) (B) from birth to 10 years.
3.3. Associations with trajectories of exposure
Four different groups of NDVI trajectories within 500 m were identi- fied by the LCLMM, which are shown in Fig. 3A: descending NDVI (1), low stable levels of NDVI (2), ascending NDVI (3) and high stable levels of NDVI (4). Regarding the distance from children's residence to the nearest blue space, LCLMM identified three groups, which are depicted in Fig. 3B: stable levels (1), descending (2) and ascending (3) distance to blue space. Supplementary material Tables A.1 and A.2 show the opti- mal number of trajectory groups using the BIC and the posterior proba- bility of belonging to each latent class, respectively.
Table 4 presents the crude and adjusted associations between trajec- tories of exposure to green and blue spaces and allergic sensitization. Residing in neighbourhoods with high stable levels of NDVI throughout childhood was associated with a lower risk of allergic sensitization [HR
Our findings are in accordance with previous studies suggesting that exposure to the natural environment may be protective against allergic sensitization, although the evidence is inconsistent (Fuertes et al., 2016; Cavaleiro Rufo et al., 2019). Results from a study using two birth cohorts in northern and southern Germany (GINIplus and LISAplus) showed contrasting associations between NDVI and allergic diseases among children. In the rural North area, NDVI within 500 m was associ- ated with a lower risk of aeroallergen sensitization, while in the urban South area, NDVI was positively associated with allergic diseases (Fuertes et al., 2014). In a more extensive follow-up, including seven
Table 2
Normalized Difference Vegetation Index (NDVI) and distance to the nearest blue space around children's house by buffer size and allergic sensitization at the age of 10.
(95% CI) = 0.539 (0.301, 0.965)]. No significant associations were ob- served for the remaining trajectories and allergic sensitization (Table 4). Although not significant, a tendency towards a protective ef- fect was observed between descending residential distance to the nearest blue space and allergic sensitization [HR (95% CI) = 0.904 (0.462, 1.768)].
No significant associations were observed between NDVI trajectories
Characteristic
At birth NDVI
100 m
Allergic sensitization
Mean (standard deviation) p-Value No Yes
0.168 (0.077) 0.164 (0.073) 0.619
within 100 m and 250 m and allergic sensitization, despite the fact there was a decreasing trend in the risk of allergic sensitization at 10 years of age with increasing green space within 100 and 250 m of children's res-
250 m 0.208 (0.075) 0.204 (0.073) 0.483
500 m 0.232 (0.074) 0.225 (0.082) 0.206
Distance to blue spaces (m) 2150.9 (1521.2) 2234.3 (1595.6) 0.219
idences [high stable levels of NDVI: 100 m, HR (95% CI) = 0.768 (0.575, 1.028); 250 m, HR (95% CI) = 0.651 (0.384, 1.103); Suppl. Mat. Table A.5].
At 4 years of age NDVI
100 m 250 m
0.185 (0.073) 0.223 (0.072)
0.181 (0.073) 0.213 (0.073)
0.477
0.054
500 m 0.243 (0.070) 0.233 (0.071) 0.038
Distance to blue spaces (m) 2192.7 (1538.7) 2195.9 (1504.0) 0.230
4.Discussion
In this study, we assessed the effect of lifelong exposure to green and
At 7 years of age NDVI
100 m
0.210 (0.061)
0.203(0.061)
0.087
blue spaces surrounding the home on the development of allergic sen- sitization among children at 10 years of age, using data from a birth co- hort. Our results suggest that children with a greater exposure to green
250 m 0.237 (0.059) 0.228 (0.059) 0.052
500 m 0.243 (0.070) 0.230 (0.069) 0.009
Distance to blue spaces (m) 2180.0 (1516.6) 2232.4 (1499.7) 0.231
space (NDVI) at 10 years of age within 500 m of their residence had a lower risk of sensitization. In accordance, high stable levels of residen- tial NDVI across children's life course were associated with a lower risk of allergic sensitization. However, no significant associations were
At 10 years of age NDVI
100 m 250 m 500 m
0.213 (0.062) 0.240 (0.059) 0.254 (0.056)
0.206 (0.062) 0.232 (0.061) 0.243 (0.057)
0.163
0.055
0.006
observed between the exposure to blue space across children's life courses and allergic sensitization.
Distance to blue spaces (m) 2195.4 (1537.7) 2271.7 (1521.2) 0.191 NDVI: normalized difference vegetation index. Bold denotes significant associations.
Table 3
Associations (hazard ratios, HR, 95% confidence intervals, 95% CI) between Normalized Difference Vegetation Index (NDVI), distance to the nearest blue space and allergic sensi- tization at 10 years.
Allergic sensitization [HR (95% CI)]
of accumulation may also be important. Alternatively, there may also be time-limited critical periods during the life course in which expo- sures may affect human health (Lynch and Smith, 2005; Pearce et al., 2016). Additionally, life course approaches may provide opportunities to simultaneously understand the coevolution of individuals and neighbourhoods, and these dynamic relationships over time (Pearce,
Model 0 (n = 730)
Model 1 (n = 707)
2018). In New Zealand, children who lived in greener spaces over the life course were less likely to be asthmatic: an increase in mean lifetime
At birth 100 m
250 m 500 m
Distance to the nearest blue space (hm)
At 4 years of age 100 m
250 m 500 m
Distance to the nearest blue space (hm)
At 7 years of age 100 m
250 m 500 m
Distance to the nearest blue space (hm)
At 10 years of age 100 m
250 m 500 m
Distance to the nearest blue space (hm)
0.483 (0.100, 2.337)
0.567 (0.122, 2.648)
0.639 (0.131, 3.123)
1.001 (0.994; 1.008)
0.433 (0.084, 2.230)
0.234 (0.046, 1.183)
0.248 (0.046, 1.347)
1.000 (0.993; 1.008)
0.198 (0.028, 1.392)
0.166 (0.024, 1.151)
0.112 (0.015, 0.860)
1.002 (0.995; 1.009)
0.161 (0.025, 1.012)
0.126 (0.019, 0.814)
0.086 (0.011, 0.658)
1.003 (0.996; 1.010)
0.509 (0.095, 2.709)
0.683 (0.128, 3.632)
0.854 (0.148, 4.916)
1.003 (0.995; 1.010)
0.437 (0.073, 2.622)
0.228 (0.039, 1.351)
0.277 (0.043, 1.762)
1.001 (0.993; 1.009)
0.232 (0.029, 1.873)
0.204(0.026, 1.629)
0.141 (0.016, 1.227)
1.002 (0.995; 1.010)
0.164 (0.023, 1.192)
0.148 (0.020, 1.112)
0.095 (0.011, 0.823)
1.004 (0.996; 1.011)
NDVI and vegetation index in the children's residence was associated with a lower risk of asthma (Donovan et al., 2018). Our results suggested that the exposure effect to green space may accumulate over children's lifetime. Although we have also observed developmental periods during which the effect may be greater, our results suggested that the trajectory of accumulation may also be important. Our findings supported that both lifetime and late-childhood exposure to green space had a protective ef- fect on allergic sensitization among children at 10 years of age. Previous studies have also suggested that the protection against allergic sensitiza- tion and atopic asthma may occur throughout life, showing that immune modulation may not be fixed after the first years of life, but also that im- mune deviation may take place over the life course (Koskela et al., 2005; Douwes et al., 2007). The presence of green space in residential sur- roundings may encourage children to spend more time outdoors, offer- ing an opportunity to experience contact with nature, which may be associated with the protective effect of lifetime and late-childhood expo- sure to green spaces on allergic sensitization. This protective effect was observed for a buffer of 500 m from children's homes, but the effect dis- appeared when considering 100 and 250 m radius, suggesting that rele- vant exposures occur mainly in green spaces in extended residential neighbourhoods rather than in closer proximity to home. A larger buffer size may be more likely to also include commuting spaces and environ- ments where children spend their time, and might better reflect the po- tential effect of children's exposure to green space (Reid et al., 2018). Additionally, a smaller buffer size may capture the exposure to green spaces immediately surrounding children's homes, while a larger buffer size may capture an average walkable area (James et al., 2015).
No associations were found between distance from children's resi- dence to blue space and allergic sensitization at age 10. Previous results from 9 European cohorts also reported that blue space was not associ- ated with allergic and respiratory outcomes (Parmes et al., 2020).
NDVI: normalized difference vegetation index. Model 0: crude model; model 1: adjusted for sex, distance to the nearest major road, motorway or highway and neighbourhood so- cioeconomic deprivation, maternal educational level, and household crowding. Bold de- notes significant associations.
birth cohorts from three continents, the effect direction of NDVI also dif- fered by geographic location; green space was inversely associated with allergic disease in GINI/LISA North and PIAMA, but positively associated in BAMSE and GINI/LISA South (Fuertes et al., 2016). A study including 1044 children and adolescents aged between 0.5 and 20 years showed that the green space around homes was inversely associated with the risk of atopic sensitization (Ruokolainen et al., 2015). However, most studies have only measured exposure to green space at one point in time, which may not represent children's lifetime exposure and does not allow for the identification of critical windows of exposure. Our re- sults showed that lifetime and late-childhood (10 years of age) exposure to green space (NDVI) was protective against allergic sensitization, sug- gesting that the effects of cumulative environmental exposures over the life course and later in children's life may also be critical and perti- nent in understanding health effects. The life course approach, which in- corporates longitudinal data related to neighbourhoods, may provide insights into the accumulation of risk over time and also on crucial moments in the life course where several factors are particularly impor- tant for health outcomes (Pearce et al., 2016). This approach has been essential in establishing that exposure effects may accumulate over the life course and influence health later in life, suggesting that the trajectory
While evidence highlighting the effect of blue space on human health is increasing (Gascon et al., 2017), our study is the first assessing the ef- fect of exposure to blue space on allergic sensitization in children. A pre- vious meta-analysis showed that blue spaces can mitigate temperature over 2 °C during the summer (Völker et al., 2013), which may lead to a decrease in air pollution (Kalisa et al., 2018), and consequently to a lower risk of allergic sensitization (Bowatte et al., 2015). Furthermore, blue space has been associated with lower levels of environmental stressors, such as air pollutants (Markevych et al., 2017). The difference between our results and those reported by previous studies could par- tially be due to the distance from home to the nearest blue space, which may represent a lower exposure to blue space and its recreational use (Elliott et al., 2020).
Several mechanisms may be implicated in the association observed between green space and allergic sensitization. Urban green space may act as a buffer against exposure to air pollution, by removing pol- lutants from the atmosphere, and as a physical barrier that increases pollutant dispersion and in inhibiting wind flow (Nowak et al., 2006; James et al., 2017). Moreover, both respiration through leaf stomata, and wet and dry deposition on the tree surface could also remove air pollutants, including particulate matter and volatile organic compounds (Niinemets et al., 2014). Tischer et al. (2017) reported an association be- tween higher residential green space and lower levels of nitric dioxide in the Euro-Siberian region, which may explain the effect of exposure to green space on wheezing. On the other hand, green space that is usu- ally characterized by higher biodiversity, which encompasses a variety of species (animals, plants and microorganisms) (Cavaleiro Rufo et al.,
Fig. 3. Normalized Difference Vegetation Index (NDVI) trajectory within 500 m the child residence (A) and residential distance to the nearest blue space (km) trajectory groups (B) from birth to 10 years.
2020b; Ferrante et al., 2020), has been suggested to influence the devel- opment of allergic sensitization through the exposure to more diverse macro and microbiota that modulate the immune system (Hanski et al., 2012; Ruokolainen, 2017). Ruokolainen (2017) and Hanski et al. (2012) showed that forest and agricultural land use around a house af- fects the composition of the skin microbiota. Compared with healthy in- dividuals, atopic 14 to 18 year old school children had a lower diversity of gammaproteobacteria on their skin, and a lower expression of IL-10, one of the key anti-inflammatory cytokines in immunologic tolerance. Additionally, food allergy has also been associated to an insufficient ex- posure to a diverse range of environmental microbiota during early life (Lee et al., 2020). A reduced contact with natural green space may ad- versely affect the assembly and composition of children's microbiota, and thereby lead to inadequate and unbalanced stimulation of immuno- regulatory circuits (von Hertzen et al., 2011), increasing the risk of food allergies (Azad et al., 2015). These results provide support for our find- ings, which highlight the effects of exposure to natural environments on allergic sensitization, reflecting immunologic responses developed by children with cumulative and late-childhood exposures to NDVI.
The current study has several limitations. NDVI is an objective mea- sure used to assess green vegetation but does provide information on the type of vegetation, accessibility, and quality of green spaces. Infor- mation on time spent outdoors and green space around other environ- ments, such as schools, were also not available, and therefore, our study was unable to determine the burden of exposures that occur in different environments. Our sample only included 730 children living in the Porto Metropolitan Area. The children included belonged to families with higher educational levels (maternal educational level >9 years was 55.2% among included participants vs. 50.4% in those excluded,
capture an individual’s true geographic context because their activities take place outside of their local residential environment (Ribeiro, 2018).
This study also presents important strengths. This is the first longitu- dinal study assessing the effect of lifelong exposure to green and blue spaces on the development of allergic sensitization in children. Our study included multiple measures of exposure to green and blue spaces from birth to 10 years of age, allowing us to assess the relationship be- tween exposure and allergic sensitization at different life stages as well as their cumulative effect. Allergic sensitization was objectively de- fined using specific IgE determination, with a strict threshold of 0.35 kU/
L. Finally, sensitivity analyses were conducted to assess the impact of the selected distance buffers (100 m, 250 m and 500 m) and the associ- ation among children who moved between birth and 10 years of age.
5.Conclusions
This is the first longitudinal birth cohort study suggesting that life- long exposure to NDVI may have a protective effect on allergic sensitiza- tion among children at 10 years of age. Moreover, our results showed that 10 years of age may also be a critical and pertinent moment for the development of allergic sensitization among children exposed to
Table 4
Associations (hazard ratios, HR, 95% confidence intervals, 95% CI) between trajectories of Normalized Difference Vegetation Index (NDVI) within 500 m and of distance to the nearest blue spaces and allergic sensitization at 10 years.
Allergic sensitization [HR (95% CI)]
p = 0.013) and lived in households with fewer occupants (household crowding <1.5 was 85.9% among included participants vs. 81.8%
Model 0 (n = 730)
Model 1 (n = 707)
among those excluded, p = 0.007). Additionally, the mean (SD) dis- tance from children's residences to blue space at birth was lower among included participants than in those excluded [5421.4 (2572.0) m vs. 6782.7 (30,017.1) m, p = 0.014]. Although the differences be- tween the included and excluded children were relatively small, our sample may not fully represent the socioeconomic and environmental conditions of the initial cohort participants. Finally, in line with similarly to other studies on neighbourhood health effects, our work may be af-
NDVI Descending
Low stable levels Ascending
High stable levels Distance to blue spaces
Stable levels Descending Ascending
Reference
0.632 (0.374, 1.070) 0.704 (0.351, 1.412) 0.549 (0.310, 0.975)
Reference
0.912 (0.469, 1.772) 1.166 (0.576, 2.358)
Reference
0.627 (0.365, 1.076) 0.682 (0.331, 1.405) 0.539 (0.301, 0.965)
Reference
0.904 (0.462, 1.768) 1.234 (0.604, 2.518)
fected by the Uncertain Geographic Context Problem (UGCoP). The UGCoP occurs whenever the method to delimitate a person's neighbourhood (e.g. the use of a certain buffer size/shape) does not
Model 0: crude model; model 1: adjusted for sex, distance to the nearest major road, mo- torway or highway and neighbourhood socioeconomic deprivation, maternal educational level, and household crowding. Bold denotes significant associations.
NDVI. Our findings could have important public health and urban plan- ning implications, suggesting that the provision of green spaces in the residential neighbourhoods of metropolitan areas may be an effective strategy to promote children's health as well as prevent allergic and re- spiratory diseases.
CRediT authorship contribution statement
Inês Paciência: Methodology, Formal analysis, Investigation, Writ- ing – original draft, Writing – review & editing. André Moreira: Concep- tualization, Writing – review & editing, Supervision. Carla Moreira: Methodology, Formal analysis, Writing – review & editing. João Cavaleiro Rufo: Formal analysis, Writing – review & editing. Oksana Sokhatska: Investigation, Writing – review & editing. Tiago Rama: In- vestigation, Writing – review & editing. Elaine Hoffimann: Investiga- tion, Writing – review & editing. Ana Cristina Santos: Writing – review & editing, Supervision. Henrique Barros: Supervision, Writing – review & editing. Ana Isabel Ribeiro: Methodology, Formal analysis, Investigation, Supervision, Writing – review & editing.
Declaration of competing interest
The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influ- ence the work reported in this paper.
Acknowledgements
The authors gratefully acknowledge the families enrolled in Genera- tion XXI for their kindness, all members of the research team for their enthusiasm and perseverance and the participating hospitals and their staff for their help and support.
Funding
The EXALAR 21 project was funded by the European Regional Development Fund (FEDER), through the Competitiveness and Internationalization Operational Programme, and by national funding from the Foundation for Science and Technology (FCT) under the scope of the project PTDC/GES-AMB/30193/2017 (POCI-01-0145-FEDER- 030193, 02/SAICT/2017 - Project n° 30193). This study was also funded by FEDER through the Operational Programme Competitiveness and Internationalization and national funding from the Foundation for Science and Technology – FCT (Portuguese Ministry of Science, Technol- ogy and Higher Education) under the Unidade de Investigação em Epidemiologia - Instituto de Saúde Pública da Universidade do Porto (EPIUnit) (UIDB/04750/2020). G21 was funded by Programa Operacional de Saúde – Saúde XXI, Quadro Comunitário de Apoio III and Administração Regional de Saúde Norte (Regional Department of Ministry of Health). Ana Isabel Ribeiro was supported by National Funds through FCT, under the programme of ‘Stimulus of Scientific Employ- ment – Individual Support’ within the contract CEECIND/02386/2018. Ana Cristina Santos holds a FCT Investigator contracts IF/01060/2015.
Appendix A. Supplementary data
Supplementary data to this article can be found online at https://doi. org/10.1016/j.scitotenv.2021.145394.
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