Long-term air pollution exposure increases asthma risk in children and adults

Long-term exposure to PM2.5 pollution significantly raises asthma risk for children and adults, contributing to around 30% of global asthma cases.

Study: Long-term exposure to PM2.5 has significant adverse effects on childhood and adult asthma: A global meta-analysis and health impact assessment. Image Credit: Shutterstock AI/Shutterstock.com

In a recent study published in One Earth, researchers review existing evidence on the effects of long-term exposure to air pollution in the form of fine particulate matter on the risk of developing asthma.

Global burden of asthma

Over 250 million people worldwide are currently living with asthma, with symptoms like wheezing and coughing that can severely impact an affected individual’s quality of life and, in severe cases, be life-threatening. Managing asthma requires ongoing medication and healthcare, thus creating financial strain on individuals and society.

Exposure to particulate matter 2.5 microns or less in diameter (PM_2.5) over long periods is a potential risk factor for asthma; however, previous studies on this association have shown inconsistent results. Furthermore, many of these studies have been conducted in high-income countries, thus limiting their generalizability to other regions of the world.

Additional research is needed to clarify the relationship between asthma and PM_2.5, as air pollution is a modifiable risk factor. Conclusive evidence on this association could also support the development of policies and personal actions that can reduce exposure.

Linking asthma to air pollution

In the current study, researchers performed a systematic review of long-term PM_2.5 exposure and asthma risk on 1,027 records obtained from studies involving over 25 million participants across 22 countries.

Meta- and exposure-response analyses were performed to assess the impact of PM_2.5 exposure on asthma risk. Asthma-related health burdens due to PM_2.5 exposure were calculated and compared to burdens from other diseases linked to PM_2.5, like lung cancer.

The initial review identified 3,406 studies, 41 of which examined childhood asthma and 18 on adult asthma. The included studies represented a wide global PM_2.5 exposure, with over 90% of the global population considered.

Increasing PM_2.5 concentrations by 10 µg/m³ was associated with a 21.4% increase in all types of childhood asthma and a 7.1% increase in adult asthma. Greater asthma risk was associated with exposure to PM_2.5 in early life, with this risk increasing with age. However, high variation was observed across studies, which the researchers attributed to different methods used to assess exposure and different compositions of PM_2.5.

Policy implications

The prevalence of asthma has significantly risen throughout the world since the 21^st century, particularly in low- and middle-income countries. About 4% of the global population has asthma, with 30 million new cases diagnosed each year.

In the current study, researchers found evidence of a linear relationship between PM_2.5 levels and asthma risk. In 2019, approximately one in three asthma cases globally were linked to PM_2.5 exposure.

Children are at a greater risk of developing asthma from PM_2.5 exposure, which may be due to higher age-related vulnerability. Currently, there is limited evidence of the effects of PM_2.5 exposure on asthma mortality, as most studies have focused on asthma prevalence and incidence.

Each PM_2.5 component affects asthma differently; for example, organic matter and black carbon have stronger impacts than inorganic particles. Other pollutants are often correlated with PM_2.5; however, adjusting for these pollutants does not significantly impact the association between PM_2.5 and asthma.

Overall, the study findings highlight the importance of reducing air pollution, particularly from PM_2.5, to reduce the risk of asthma in adults and children globally. Stronger air quality legislation could reduce the burden of asthma and significantly improve public health.

Strengths and limitations

Notable limitations of the current study include various methods used to measure PM_2.5, with inaccuracies that could lead to biased estimates of risk. Future studies utilizing high-resolution data could improve the accuracy of these measurements. Heterogeneity among different studies also emphasizes the need to standardize methods for measuring PM_2.5 exposure and diagnosing asthma.

Some strengths of the current study include its large and geographically diverse sample, as well as the use of strict data criteria for bias minimization and enhanced robustness of the results. Nevertheless, there remains a lack of high-quality longitudinal studies conducted in low- and middle-income countries.

Conclusions

The researchers of the current study performed a comprehensive global meta-analysis of over 25 million individuals, including data from low- and middle-income countries. Herein, long-term PM_2.5 exposure was found to significantly increase the risk of asthma for both adults and children.

Our findings highlight the urgent need for policymakers to enforce stringent legislation to continuously combat air pollution, while personal maneuvers, such as wearing masks, can also help reduce individual exposure and mitigate asthma risk.”