Title: Atopic sensitization in childhood depends on the
type of green area around the home in infancy
Tiia Voor1,2*, Meelis Pärtel3*,
Aleksandr Peet1,2, Liisa Saare1,2,
Heikki Hyöty4,5, Mikael Knip6,7,
John Davison3, Martin Zobel3#,
Vallo Tillmann1,2#
1 Children´s Clinic of Tartu University Hospital,
Estonia
2 Institute of Clinical Medicine, University of Tartu,
Estonia
3 Institute of Ecology and Earth Sciences, University
of Tartu, Estonia
4 Faculty of Medicine and Health Technology, Tampere
University, Finland
5 Fimlab Laboratories, Pirkanmaa Hospital District,
Tampere, Finland6 Pediatric Research Center, New Children’s Hospital,
Helsinki University Hospital, Helsinki, Finland7 Research Program for Clinical and Molecular
Metabolism, Faculty of Medicine, University of Helsinki, Helsinki,
Finland
To the editor,
The prevalence of allergy has increased worldwide (1) and a green
environment is essential in developing immune responses and may protect
against allergy (2, 3). However, previous studies have not distinguished
the effects of different green area types.
Here we tested how the type and spatial scale of green area around the
infancy home are associated with atopic sensitization up to the age of 9
years.
The study group comprised 280 children from the Estonian DIABIMMUNE
project birth cohort (4) whose sera were measured for different
allergen-specific IgE (sIgE) antibodies at the ages 0.5, 1.5, 3, and 9
years. Subjects were divided into 3 groups by sIgE results. 86 children
who had at least one sIgE ≥0.7 kU/L were categorized into the group of
definite atopic sensitization (Group I); 44 children had some sIgE
between 0.35-0.69 kU/L and were classified as uncertain sensitization
(Group II); 150 children had all measured sIgE below 0.35 KU/L, and they
formed the control group (Group III). The types of surrounding green
areas during the first six months of life were obtained from digital
maps of Estonia. The land was divided into agricultural fields, forests,
grasslands and wetlands (Figure 1A).
The combination of various green area types at a radius of 1-10 km
around homes in infancy was related to signs of atopy by ordinal
regressions, and model weights were compared.
This is the first study addressing the correlation between the land-use
intensity around child homes and the development of atopic
sensitization. A model with the green areas within 8 km had the highest
protective weight (Fig. 1B). Among the various types of green areas, the
impact of forests was the largest (Fig. 1C), but the best model also
included grasslands and wetlands. Agricultural fields had an impact only
at 1-2 km scales, and their weight declined strongly at larger scales
(Table 1). We used the best model (area of forest, grasslands and
wetlands within 8 km) and examined how it predicts atopic sensitization
groups (Fig. 1D). The model predicted a decrease in Group I and an
increase in control Group III. The uncertain Group II showed a slightly
decreasing tendency. The protective effect of forests, grasslands and
wetlands against sensitization was evident for both inhaled and food
allergens.
The world is urbanizing, and the isolation of humans from biodiverse
green areas leads to reduced contact with beneficial environmental
microbes (5). Ruokalainen et al (2) showed that the greenness around
homes was negatively associated with the risk of atopy in children.
Contact with natural soil enriched microbiota enhanced immune regulation
and may reduce the risk of development of immune-mediated diseases (6).
Our results reveal considerable differences in how various green area
types might prevent atopic sensitization. The area of biodiverse land
(forests, grasslands, wetlands) showed a strong protective effect, while
the agricultural land did not. The positive effect of forests,
grasslands and wetlands became clearer with increasing spatial scale.
The relatively large distance of influence indicates that the
biodiversity of beneficial microbes might need a large area.
Our study has some limitations. First, we could not study the microbiota
of the participants and determine whether the spatial environmental
model explained microbiota composition. Secondly, we studied only atopic
sensitization and did not diagnose allergic disease. This was because
the data were collected using questionnaires completed by parents and
were of variable quality.
In conclusion, the current results indicate that biodiverse land – such
as forests, grasslands, and wetlands – around homes during infancy
elicits a strong protective effect against the development of atopy
later in childhood. At the same time, intensive croplands have only a
very weak effect.