The combination of air pollution, dense urban development and limited green spaces increases the risk of asthma in both children and adults. This is shown by a new study conducted as part of a major EU collaboration led by researchers from Karolinska Institutet.
The study covers nearly 350,000 people of different ages, from 14 cohorts in seven European countries. Information on home addresses of each individual made it possible to link data on various environmental risks in the urban environment to individual people. The environmental exposures included were air pollution, outdoor temperatures, and the level of urban density. The assessment was partly based on satellite images showing grey, green, or blue areas, i.e., where there were buildings, green spaces, or water.
"Previous studies have typically calculated the risk of one environmental factor at a time. We have combined several environmental factors and described how they together affect the risk of developing asthma. This provides a better picture of environmental risks, as life in a city usually involves exposure to several environmental risk factors at the same time," says first author Zhebin Yu, researcher and assistant professor at the Institute of Environmental Medicine at Karolinska Institutet.
During the study period, nearly 7,500 of the study participants developed asthma as children or adults. The researchers found that 11.6 per cent of asthma cases could be explained by the combination of environmental factors. Or, to put it another way, in a favourable environment, approximately one in ten people with asthma would not have developed the disease. The combination of air pollution, lack of green spaces, and dense urban development was most relevant for the development of asthma.
"This is useful for politicians and others involved in urban planning. The method makes it possible to identify risk areas in existing urban areas, but it can also be used when planning future urban environments," says Erik Melén, professor at the Department of Clinical Research and Education, Södersjukhuset, and last author of the study.
The next step for the researchers is to examine blood samples from some of the study participants. The aim is to identify their metabolome, i.e., a composite picture of the body's metabolism and breakdown products. The purpose is to understand how external environmental factors affect the body, which could provide a better understanding of how asthma develops.
The study was conducted in collaboration between various research groups within the framework of the EU project EXPANSE. The researchers involved in the project are also investigating how the risk of other diseases such as stroke, heart attack, COPD and diabetes, is affected by individual exposomes, i.e., the total exposure to many environmental factors.
The study was funded by the EU's Horizon 2020 programme (EXPANSE, No 874627), the Swedish Research Council, Forte (the Swedish Research Council for Health, Working Life and Welfare), the Swedish Heart-Lung Foundation and Region Stockholm, among others.
