Short-term Air Pollution Exposure and Risk of Airway Inflammatory Response in Children (CHERISH): Protocol for a Randomised Mixed Factorial Study

Introduction

Air pollution is the largest environmental risk to human health. Children are disproportionately affected by air pollution and their exposure is amplified during physical activity. Observed concentrations of nitrogen dioxide in 1 in 4 London school playground exceeds the European limit, but the health impacts of air pollution exposure in London school playgrounds remain unexplored. Our study aims to assess and compare the acute changes in lung function and airway inflammation of primary school-aged children exercising in school playgrounds.

Methods and analysis

330 children aged 8–11 years from ten London schools will be recruited to complete 90 minutes of physical activity and 90 minutes of rest in their school playground in a randomised crossover design. Pre-, post-, and 24-hour post-exposure oscillometry measurements will be performed with airway resistance at 5 Hz (R5) the primary physiological outcome. Nasal lavage samples will be collected pre-exposure and 24-hour post-exposure for analysis of inflammatory, oxidative, and vascular biomarkers, with IL-6 as the primary biological outcome. Mixed-effects regression models will examine associations between estimated pollutant exposures, exercise and physiological responses.

Ethics and Dissemination

This study has been approved by Queen Mary Ethics of Research Committee (QME25.1220). The study will be conducted according to the principles of the Helsinki Agreement (2013). Findings will be published in a peer-reviewed journal and shared at national and international conference presentations. This study will provide the first evidence on the short-term respiratory and immunological impacts of air pollution exposure during physical activity in London school playgrounds, supporting future public health guidance, school policy, and clinical advice for children, including those with asthma.

Strengths and limitations of this study

• This study uses a randomised crossover design, allowing each child to act as their own control and reducing inter-individual variability in physiological responses.

• The study includes a large sample of 330 children from 10 London schools, providing sufficient statistical power and enabling assessment across a gradient of real-world air pollution exposures.

• Conducting the study during typical school playground activities enhances ecological validity and ensures findings are directly relevant to real-world school environments.

• As exposures occur in natural outdoor settings, air pollution levels and meteorological conditions cannot be fully controlled, which may introduce variability in exposure estimates.

• The study examines short-term physiological and immunological responses only, and therefore cannot determine the long-term health impacts of repeated exposure