A study links air pollution, dense urban development, and a lack of green spaces to asthma risk

A combination of air pollution, densely built urban environments, and limited green spaces increases the risk of asthma in both children and adults. This conclusion comes from a recent study conducted as part of a large European Union research collaboration, led by scientists from Karolinska Institute in cooperation with the Institute of Genomics at the University of Tartu.

Previous studies have typically assessed the impact of individual environmental factors separately, but this research combined multiple factors to demonstrate how they collectively influence asthma risk. "This project is one of the first to examine how urban environmental factors interact in the development of asthma. Additionally, it offers comparisons between different national cohorts and a methodology for conducting such comparisons," said one of the study's authors, biostatistician Hanna-Maria Kukk from the Institute of Genomics.

The study included nearly 350,000 individuals of different ages from 14 European countries, allowing researchers to link environmental risks to specific individuals based on their home addresses. The analysed environmental factors included air pollution, outdoor temperature, and urban development density. Part of the assessment was based on satellite images, which enabled modelling of the proportions of built areas (grey), vegetation (green), and water bodies (blue) within people's living environments.

During the study period, around 7,500 people developed asthma, either in childhood or adulthood. According to the researchers, 11.6% of asthma cases could be attributed to a combination of environmental factors. In other words, with a more favourable living environment, roughly one in ten asthma cases might have been prevented. The most significant factors in asthma development were air pollution, the absence of green spaces, and densely populated urban areas.

System biology researcher Jaanika Kronberg noted that the Institute of Genomics team analysed Estonian Biobank participants at different time points. "Looking specifically at Estonia, we see that people in areas with moderate urbanization have a higher asthma risk compared to those in highly urbanized regions with very little green space or those in rural areas with abundant greenery," said Kronberg, adding that these high-risk areas are likely small towns or residential districts with private homes in larger cities.

Ongoing Research

This asthma study was conducted within the international EXPANSE project. Next, researchers plan to analyse blood-based biomarkers in a subset of participants to understand how environmental factors impact metabolism and disease development. "The focus of this study was asthma, but we are already investigating cardiovascular and metabolic diseases, as well as environmental links to cancer. Future research will explore the interaction between genetic and environmental risks," Kronberg explained.

One of the lead authors, Professor Erik Melén, emphasised that this kind of information is highly valuable for policymakers and urban planners, as the method allows for identifying high-risk areas within existing cities and planning healthier urban environments in new developments.

Read the full study: External exposome and incident asthma across the life course in 14 European cohorts: a prospective analysis within the EXPANSE project.