Asthma is one of the most prevalent chronic diseases worldwide , affecting around 260 million people.
Authors
- Zhebin Yu
Postdoctoral researcher in Environmental Medical Epidemiology, Karolinska Institutet
- Erik Melen
Professor of Paediatrics, Karolinska Institutet
Researchers have long know that environmental factors, such as air pollution and lack of green spaces , are linked to respiratory diseases such as asthma. But the joint impact of these various environmental factors on a person's risk of developing asthma has, until now, remained unclear.
Our study is the first to reveal the joint impact of multiple environmental factors in urban areas, known as the urban exposome, on the risk of developing asthma . We found that air pollution, lack of green space and areas built primarily from concrete and asphalt are linked with significantly greater risk of developing the condition.
To conduct our study, we analysed data from 349,037 participants from across 14 cohorts in Europe. Participants ranged in age from birth to 70 years old.
We also linked three major external environmental factors - air pollution, the built-up environment (such as the amount of green space a person had access to or the amount of artificial light they were exposed to at night) and ambient temperature - to participants' home addresses at the beginning of the study.
Participants were then grouped based on their exposure levels to the three major environmental factors. This allowed us to examine how exposure was linked to the onset of asthma and also calculate what a person's risk of developing asthma would be if exposed to these environmental conditions.
We also accounted for factors that might have affected the results, such as a person's age, sex, ethnic background, weight, socioeconomic status and whether they smoked (or were exposed to smoke).
We found that adults living in areas with high levels of air pollution had a 13% higher risk of developing asthma compared to people living in low pollution areas. Children living in high pollution areas had an 18% greater risk of developing asthma.
Adults living in areas that lacked green space had a 15% greater risk of developing asthma, while children had a 38% greater risk.
But one of the most significant findings of our study was just how much joint exposure to these environmental factors contributed to new asthma cases in both children and adults.
We found that the most hazardous urban environments were those characterised by high levels of air pollution, limited access to green spaces and those that were built primarily from concrete and asphalt. This increased an adult's risk of asthma by 27% and a child's risk of asthma by 35%.
Even areas without high levels of air pollution, but which were built primarily from concrete and asphalt and lacked green spaces, increased asthma risk by as much as 36%.
Urban planning and asthma risk
Our findings are generally consistent with what previous studies have found on the effects of urban environments , air pollution and green space on asthma risk. However, our study is the first to look at asthma incidence in both adults and children.
It's also the first study to cover the entire life-course and illustrate how multiple aspects of the urban exposome affect asthma incidence in all age groups.
It underscores the critical role that urban environments play in shaping respiratory health. We calculated that a significant proportion of asthma cases - almost 12% - could be directly attributed to urban environments.
Exposure to a combination of air pollution, poor urban planning and extreme temperatures are a significant driver of asthma risk across a person's lifespan.
With more people moving to cities every year, it's essential that we rethink how we design and manage urban spaces to prioritise health and wellbeing. Cities can help prevent asthma and improve quality of life by introducing policies that aim to reduce air pollution, expand green spaces and design infrastructure that is more resilient to extreme temperatures.
Zhebin Yu receives funding from Swedish Research Council and Swedish Research Council for Health, Well-being and Welfare.
Erik Melen receives funding from the Swedish Research Council, the Swedish Heart-Lung Foundation and Region Stockholm. Melen has also received advisory board or lecture fees from ALK, AstraZeneca, Chiesi and Sanofi outside the present study.
