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Vegetation diversity protects against childhood asthma: results from a large New Zealand birth cohort

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We assessed the association between the natural environment and asthma in 49,956 New Zealand children born in 1998 and followed up until 2016 using routinely collected data. Children who lived in greener areas, as measured by the normalized difference vegetation index, were less likely to be asthmatic: a 1 s.d. increase in normalized difference vegetation index was associated with a 6.0% (95% CI 1.9–9.9%) lower risk of asthma. Vegetation diversity was also protective: a 1 s.d. increase in the number of natural land-cover types in a child’s residential meshblock was associated with a 6.7% (95% CI 1.5–11.5%) lower risk. However, not all land-cover types were protective. A 1 s.d. increase in the area covered by gorse (Ulex europaeus) or exotic conifers, both non-native, low-biodiversity land-cover types, was associated with a 3.2% (95% CI 0.0–6.0%) and 4.2% (95% CI 0.9–7.5%) increased risk of asthma, respectively. The results suggest that exposure to greenness and vegetation diversity may be protective of asthma.
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Articles
https://doi.org/10.1038/s41477-018-0151-8
© 2018 Macmillan Publishers Limited, part of Springer Nature. All rights reserved. © 2018 Macmillan Publishers Limited, part of Springer Nature. All rights reserved.
1Center for Public Health Research, Massey University, Wellington, New Zealand. 2USDA Forest Service, PNW Research Station, Portland, OR, USA.
3National Institute of Water and Atmospheric Research, Auckland, New Zealand. *e-mail: gdonovan@fs.fed.us
Since the pioneering work of Roger Ulrich1—who found that
patients with a view of a natural scene recovered more quickly
from surgery—research has shown that exposure to the natural
environment is associated with a wide range of beneficial health out-
comes, including lower mortality2,3, higher birth weight26, reduced
risk of cardiovascular disease7 and improved mental health8,9.
However, most studies have used a cross-sectional study design that
measured the natural environment and health outcomes at the same
point in time. This is a major limitation, as the health consequences
of environmental exposures often do not manifest immediately10,
and timing of exposure across the life course may strongly affect
the outcome, with the first few years of life believed to be particu-
larly critical11. In addition, past studies have relied heavily on a sin-
gle measure of overall greenness called the normalized difference
vegetation index (NDVI), which is typically derived from satellite
imagery. However, markedly different landscapes can have similar
NDVI values, so the use of NDVI has limited researchers’ capacity
to determine which aspects of the natural environment provide the
greatest public-health benefits.
Several recent studies suggest that exposure to the natural envi-
ronment may be protective of asthma, although the evidence is
mixed12. Asthma is a chronic health condition that affects 334 mil-
lion people worldwide and its prevalence is increasing13. Although
asthma treatment has improved, it is not effective for all asthmat-
ics, and there is no cure. In addition, there are limited public-health
interventions that can reduce asthma risk, and these interventions
are often difficult to implement. Therefore, there is considerable
interest in understanding how exposure to the natural environment
may protect against asthma and in identifying what specific aspects
of the natural environment afford the most protection.
An ecological study in 42 health catchment areas in New York
City14 showed that areas with more street trees within 1 square kilo-
metre had lower rates of asthma among 4–5 year olds, but there
was no relationship between tree density and hospitalizations for
asthma. A follow-up study15, using individual-level data from 549
African American and Dominican children, who lived in socially
deprived neighbourhoods in New York City, found that tree cover
was not protective of asthma. Furthermore, more trees within 250 m
of the prenatal address was a risk factor for allergic sensitization.
In a 10-year follow-up study of a large (n = 65,000) birth cohort
in Vancouver, British Columbia16, it was found that greenness was
protective of early-life asthma, but not of school-age asthma. The
authors measured greenness using NDVI. The results held after
controlling for air pollution and proximity to major roads. A study17
on greenness (measured using NDVI) and asthma rates in 14 met-
ropolitan statistical areas in Texas found no association, although
this may be an artefact of the ecological study design and small
sample size.
A study18 in 3,178 9–12 year olds in Sabadell, Spain, found no
relationship between greenness around a child’s residential address
(NDVI in buffers of 100 m to 1,000 m) and asthma. However, chil-
dren who lived closer to a park were at greater risk, which the
authors speculate may be because parks in Catalonia have more
non-native species than other green areas.
A recent cross-sectional study19 in Australia, not focused exclu-
sively on asthma, examined the relationship between the natural
environment and rates of hospital admission for respiratory disease
in local government areas. They found that multiple measures of the
natural environment were protective of a respiratory disease.
One reason for the observed inconsistent association between
the natural environment and asthma may be that NDVI is a rela-
tively coarse measure of greenness: different plants can have similar
spectral profiles. In addition, most studies only measured greenness
at one point in time and a single measure is unlikely to accurately
represent a child’s lifetime exposure. Indeed, using a one-point-in-
time measure may result in systematic measurement error as dem-
onstrated previously by Brokamp et al.20. The authors tracked all
the residential addresses (from birth to age 7) of a cohort of 613
children in Cincinnati, OH, and showed that, across time, children
moved to less socially deprived, greener neighbourhoods, with
Vegetation diversity protects against childhood
asthma: results from a large New Zealand birth
cohort
Geoffrey H. Donovan 1,2*, Demetrios Gatziolis2, Ian Longley3 and Jeroen Douwes1
We assessed the association between the natural environment and asthma in 49,956 New Zealand children born in 1998 and
followed up until 2016 using routinely collected data. Children who lived in greener areas, as measured by the normalized
difference vegetation index, were less likely to be asthmatic: a 1 s.d. increase in normalized difference vegetation index was
associated with a 6.0% (95% CI 1.9–9.9%) lower risk of asthma. Vegetation diversity was also protective: a 1 s.d. increase in
the number of natural land-cover types in a child’s residential meshblock was associated with a 6.7% (95% CI 1.5–11.5%) lower
risk. However, not all land-cover types were protective. A 1 s.d. increase in the area covered by gorse (Ulex europaeus) or exotic
conifers, both non-native, low-biodiversity land-cover types, was associated with a 3.2% (95% CI 0.0–6.0%) and 4.2% (95%
CI 0.9–7.5%) increased risk of asthma, respectively. The results suggest that exposure to greenness and vegetation diversity
may be protective of asthma.
NATURE PLANTS | VOL 4 | JUNE 2018 | 358–364 | www.nature.com/natureplants
358
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... A recent meta-analysis reported that vegetation near homes was negatively associated with childhood asthma risk, with an odds ratio (OR) of 0.88 [14]. In more detailed analyses, farms [15,16] and natural land-cover types seemed to have a protective effect against asthma [17]. In other studies, however, grass and gardens [18] and coniferous forests [18,19] were found to be associated with more respiratory disease. ...
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Background Wheezing illnesses, especially those triggered by rhinovirus infection, cause a major disease burden, and they often precede asthma. Environmental exposures are known to affect recurrence of wheezing. We investigated the relations of population density, greenness (forested areas), and socioeconomic factors of the living surroundings to the burden of asthma in children with prior bronchiolitis. Methods Three hundred and ninety‐four children, aged 0–24 months, with doctor‐diagnosed bronchiolitis were enrolled in the MARC‐30 Finland study. We assessed the children's early‐life exposures to greenness and socioeconomic factors using time‐series of Corine Land Cover data and Statistics Finland's grid data. We compared the living surroundings data to the prescription drug purchases and special asthma reimbursement benefits until the age 8 years; asthma data were from the Social Insurance Institution of Finland. Results Children living in sparsely populated areas had lighter asthma disease burden than children living in densely populated ones, with burden measured in median bronchodilator (50DDD [defined daily dose] vs. 104DDD, p = 0.02) and inhaled corticosteroid (0DDD vs. 123DDD, p = 0.04) purchases. In the subgroup of children with rhinovirus‐induced bronchiolitis, children living in more forested areas developed asthma 10 months later than those with less forested areas ( p = 0.04). Neighborhood socioeconomic characteristics were not associated with differences in asthma burden. Conclusions Sparsely populated areas and forested environments seem to have a beneficial association with children's respiratory health. These findings warrant further studies on the protective health effects of greenness and the type of biodiversity around homes.
... In some of the studies, these inequalities are associated with inequalities (self-reported or otherwise measured) in health and wellbeing outcomes. Donovan et al. [86] assessed the association between the natural environment and asthma in a large sample of 18-year-old AoNZ children. Children who lived in greener areas (measured by the normalised difference vegetation index (NDVI)), were less likely to be asthmatic, and the NDVI was more protective when the analysis was restricted to children living in more socially deprived neighbourhoods. ...
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We have shown that viruses are associated with 80 to 85% of asthma exacerbations in school-age children in the community. We hypothesize that viral infections are also associated with severe attacks of asthma precipitating hospital admissions. To investigate this, we conducted a time-trend analysis comparing the seasonal patterns of respiratory infections and hospital admissions for asthma in adults and children. During a 1-yr study in the Southampton area of the United Kingdom, 108 school-age children monitored upper and lower respiratory symptoms and took peak expiratory flow rate (PEFR) recordings. From children reporting a symptomatic episode or a decrease in PEFR. samples were taken for detection of viruses and atypical bacteria. A total of 232 respiratory viruses and four atypical bacteria were detected. The half-monthly rates of upper respiratory infection were compared with the half-monthly rates for hospital admissions for asthma (International Classification of Diseases [ICD] code 493) for the same time period for the hospitals serving the areas from which the cohort of schoolchildren was drawn. The relationships of upper respiratory infections and hospital admissions for asthma with school attendance were studied. Strong correlations were found between the seasonal patterns of upper respiratory infections and hospital admissions for asthma (r = 0.72; p < 0.0001). This relationship was stronger for pediatric (r = 0.68; p < 0.0001) than for adult admissions (r = 0.53; p < 0.01). Upper respiratory infections and admissions for asthma were more frequent during periods of school attendance (87% of pediatric and 84% of total admissions), than during school holiday periods (p < 0.001). These relationships remained significant when allowance was made for linear trend and seasonal variation using multiple regression analysis (p < 0.01). Not surprisingly, school attendance, because it is a major factor in respiratory virus transmission, was found to be a major confounding variable in children. This study demonstrates that upper respiratory viral infections are strongly associated in time with hospital admissions for asthma in children and adults. Rhinoviruses were the major pathogen implicated, and the majority of viral infections and asthma admissions occurred during school attendance. Comments. The relationship between rhinovirus infection and hospitalization for asthma was strongest in children. Intuitively. I think we all know that "URI'S" are associated with asthmatic attacks in children, but this paper proves the point.