A landmark study of more than 3,400 children, led by Queen Mary University of London, has found that air quality improvements following the introduction of London's Ultra Low Emission Zone (ULEZ) are strongly associated with accelerated lung growth in children.
The findings suggest that improvements in air quality helped restore lung growth previously stunted by exposure to air pollution. The study, published today in The Lancet Public Health, was led by researchers from Queen Mary University of London in collaboration with Imperial College London and the Universities of Bedfordshire, Oxford, Cambridge, Edinburgh and Southern California and funded by the National Institute for Health and Care Research (NIHR).
The five-year Children's Health in London and Luton (CHILL) study set out to determine if air quality improvements following the introduction of the ULEZ, the world's largest and most ambitious clean air zone, could improve impaired lung growth of children living in London.
Working closely with schools and parents prior to the implementation of the ULEZ, the researchers recruited over 3,400 children aged 6-9 from 84 primary schools in London and Luton, with Luton acting as a comparison (control) site with a similar mix of traffic pollutants but no clean air zone.
The children's lung size and health were measured and monitored at annual school visits from 2018 to 2022 to assess the impact of air quality changes on their lung development, following the introduction of the ULEZ in London. Initial lung capacity measurements taken before the ULEZ was introduced showed that children in London had significantly smaller lungs compared to children living in Luton, a finding consistent with the team's previous work.
Looking at data collected over the five years, the team found that after the implementation of the ULEZ, London children's lungs size and health accelerated and improved to be comparable with that of children in Luton. Most importantly, they demonstrated that these improved lung growth trajectories were strongly related to air quality improvements following the implementation of the ULEZ.
The team evaluated children's lung health and development by accurately assessing their forced expiratory volume in one second (FEV1), a measurement of how much air can be forcefully exhaled from the lungs in one second following maximal inhalation, in relation to exposure to nitrogen dioxide (NO2), the pollutant most reflective of exhaust pollution.
The researchers found that within the five years after ULEZ's introduction, London children's exposure to NO2 fell twice as fast and more than twice as much compared to children in Luton.
They then demonstrated that as NO2 exposure decreased, London children's FEV1 increased by 10ml per year more than children in Luton. At the end of the five years, the FEV1 was the same across children in London and Luton, indicating that the London children's lung growth had accelerated during the five years to 'catch up' with the control group in Luton.
Over the course of the study, the team noted that the proportion of children with clinically impaired lung function fell from 14% to 9% in London, compared with a fall from 9% to 7% in Luton.
Failure to reach fully developed lungs by early adulthood increases the risk of children experiencing respiratory diseases such as asthma and COPD, cardiovascular and metabolic disease, and premature death as adults. These findings, which show that deficits in children's lung growth and health can be restored, therefore have major implications for improving the long-term health of children.
Clean air zones have been implemented in the UK, Europe, and globally. This is the first evidence that they may benefit child development and endorses their place as an important public health policy. Consideration should be given to implementing ambitious clean air zones more widely to protect and promote children's lifelong health.
Professor Chris Griffiths, Professor of Primary Care at the University of Oxford and at Queen Mary University of London, and joint senior author, said: "Traffic pollution in cities damages children's health and development. We provide the strongest evidence yet on how these harms can be prevented. Ambitious clean air zones should be considered a priority for cities globally with traffic-related air pollution".
Ian Mudway, Associate Professor in the School of Public Health at Imperial College London and joint senior author said: "Air pollution is a global issue. If we want to improve the lives of children living in high-traffic urban environments, we need bold and ambitious measures. Our data demonstrates that clean air zones can be an effective public health intervention to prevent damage to developing lungs".
Dr Helen Wood, Research Fellow at Queen Mary and lead author, said: "We already knew that the ULEZ reduced air pollution but now we know that children's lung health has improved at the same time, which is a really important finding for children and parents living in London. However, we must not be complacent - air pollution in both London and Luton – as well as other cities across the UK – remains above WHO guideline levels, so there is still work to be done."
Professor Gurch Randhawa, Professor of Public Health at the University of Bedfordshire, and joint senior author said: "The findings provide evidence of the health benefits for children living in a clean air zone. This will be of interest to Luton and Bedfordshire as they plan for future development and regeneration".
Health Minister Karin Smyth said: "This study is a powerful reminder of the impact that air quality has on children's lung health, and will help to improve our understanding of how reductions in air pollution can restore normal lung growth among children, reduce the risk of respiratory illnesses in adulthood, and support our goal to give every child the best start in life."
Professor Lucy Chappell, Chief Scientific Adviser at the Department of Health and Social Care (DHSC) and Chief Executive Officer of the NIHR, said: "This research, funded by NIHR, will provide crucial evidence on real-life interventions that deliver life-changing health benefits for children. I would like to thank the 3,400 children and their families who took part. Research can only take place with the input and support of participants, and this study is a great example of how the UK's vibrant research sector is working with communities to transform lives."
