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

The CHERISH study is a randomized mixed factorial protocol designed to assess the acute effects of short-term air pollution exposure on lung function and airway inflammation in 330 primary school-aged children exercising in London school playgrounds.

The Gist

🌬️ The Big Idea: The "Polluted Playground" Experiment

Imagine a school playground as a giant, open-air living room where kids run, jump, and play. Usually, we think of this as a healthy place to be. But in London, some of these "living rooms" are filled with invisible, harmful smoke from traffic (air pollution), much like a room filled with cigarette smoke.

The CHERISH study wants to answer a specific question: What happens to a child's lungs and immune system when they run around in this smoky room compared to when they just sit quietly in it?

While we know air pollution is bad, we don't fully understand how exercise changes the game. When you run, you breathe faster and deeper, like switching from a straw to a firehose. This means you might be swallowing a much bigger dose of the pollution than someone sitting still. This study is the first to test this theory directly in London school playgrounds.

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🎭 The Setup: A "Time-Travel" Game for Kids

The researchers are recruiting 330 children (aged 8 to 11) from 10 different schools in East and Central London. They are using a clever "crossover" design, which works like this:

1. The Two Days: Each child visits their school playground twice, with at least two weeks in between.
2. The Switch: On one day, they do a 90-minute active sports session (led by coaches from West Ham United). On the other day, they do a 90-minute quiet science workshop (led by scientists).
3. The Random Mix: Some kids do sports first, then science. Others do science first, then sports. This ensures the results aren't just because one day was windier or hotter than the other.
4. The Control: The children act as their own control group. We are comparing Child A's lungs after running vs. Child A's lungs after sitting, rather than comparing Child A to Child B.

The Goal: To see if the "firehose breathing" during exercise in a polluted playground causes more inflammation (swelling/irritation) in the airways than sitting still does.

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📏 The Tools: How They Measure the Damage

The researchers aren't just guessing; they are using high-tech tools to take "snapshots" of the children's health at specific times:

• The Lung Check (Oscillometry): Imagine blowing into a special device that sends gentle sound waves down the throat. It measures how hard it is for air to get through the tiny tubes in the lungs. If the tubes are swollen from pollution, the air has a harder time getting through (like trying to blow through a clogged straw).
• The "Snot" Sample (Nasal Lavage): This sounds gross, but it's gentle. Researchers spray a tiny bit of salt water up the child's nose and then collect it back. This water acts like a "fishing net," catching tiny bits of the immune system's reaction (like inflammatory markers) that the pollution triggered.
• The Timing: They take these measurements before the activity, immediately after, and 24 hours later. This helps them see if the irritation happens right away or if it lingers like a hangover the next day.

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📊 The Plan: What They Expect to Find

The study is looking at two main things:

1. Lung Function: Did the airways get tighter after running in the smog?
2. Inflammation: Did the immune system sound the alarm (specifically looking for a chemical called IL-6)?

The Hypothesis: The researchers suspect that running in the polluted playground will cause a bigger "alarm" in the body than sitting in the same playground. They believe the combination of exercise + pollution is a "double trouble" scenario for children's lungs.

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🛡️ Safety and Ethics: Keeping Kids Safe

• No "Danger Zones": The study will only happen on days when the air pollution is within legal limits (though it might still be higher than the World Health Organization's ideal recommendations). They won't test kids on days with toxic smog.
• Voluntary Participation: Parents sign permission slips, and the kids give their own "yes" (assent). They can stop anytime.
• Privacy: All data is locked up tight, like a secret diary, with names replaced by numbers so no one knows who is who.
• Inclusivity: The study specifically includes children from diverse backgrounds and different economic areas, ensuring the results apply to all London kids, not just a select few.

🏁 The Bottom Line

This study is like a stress test for the lungs. By comparing running vs. sitting in the same polluted air, the researchers hope to provide the first clear evidence on whether the health benefits of exercise in school playgrounds are being cancelled out by the traffic fumes.

If they find that running in polluted air causes significant inflammation, this could change how schools, parents, and doctors advise children with asthma or sensitive lungs. It might mean we need to rethink when and where kids should play outside.

Note: This is a research protocol (a plan for a study), not a report of finished results. The study is scheduled to run from late 2025 to mid-2026.

Technical Summary

Technical Summary: Protocol for the CHERISH Study

Problem Statement
Air pollution represents the largest environmental risk to human health, with children being disproportionately affected due to developing respiratory systems, higher ventilation rates relative to body mass, and increased time spent outdoors. In London, approximately one in four school playgrounds exceeds the European limit for nitrogen dioxide (NO₂). While physical activity is beneficial, it increases pollutant uptake through elevated ventilation and a shift to oral breathing. Despite evidence linking long-term exposure to reduced lung function and increased asthma risk, the short-term physiological and immunological impacts of acute air pollution exposure during physical activity versus rest in school playgrounds remain unexplored. Current literature relies heavily on adult data, which may underestimate risks for children, and no studies have directly compared the acute effects of exercise versus sedentary behavior in these specific environments.

Methodology
The CHERISH (Short-term Air Pollution Exposure and Risk of Airway Inflammatory Response in Children) study employs a randomized mixed factorial crossover design.

• Study Population: 330 children aged 8–11 years will be recruited from ten primary schools in Central and East London. Schools are purposively selected based on historical NO₂ data from the Breathe London network to ensure a gradient of traffic-related air pollution (TRAP) exposure.
• Intervention: Each participant will undergo two 90-minute exposures in their school playground, separated by a minimum two-week washout period. The order of exposure is randomized at the school level:
  1. Active Condition: A 90-minute physical education session led by coaches, maintaining moderate intensity monitored by Actigraph devices.
  2. Sedentary Condition: A 90-minute STEM workshop ("snotty science") led by outreach scientists.
• Exposure Context: Exposures occur between 10:30 AM and 1:30 PM on weekdays. Air pollution levels (NO₂, PM₂.₅, PM₁₀) are estimated using data from sensors at participating sites and historical data (October 2024–February 2025). The study acknowledges that while pollution levels generally comply with UK legal limits, they may exceed WHO health-based recommendations.
• Data Collection:
  • Physiological: Oscillometry (measuring airway resistance at 5 Hz [R5], 20 Hz [R20], and R5–20) and Fractional Exhaled Nitric Oxide (FeNO) are measured pre-exposure, immediately post-exposure, and 24 hours post-exposure.
  • Biological: Nasal lavage samples are collected pre-exposure and 24 hours post-exposure. These are analyzed for a comprehensive panel of biomarkers, including inflammatory cytokines (IL-6, IL-1β, IL-8, TNFα, IL-4, IL-5, IL-10, IL-23), oxidative stress markers (Glutathione, LOPs), vascular markers (VEGF, E-selectin), and cytotoxic markers (Granzyme A/B).
  • Primary Outcomes: The primary physiological outcome is airway resistance (R5); the primary biological outcome is IL-6.
• Statistical Analysis: Mixed-effects regression models will be used to assess associations between estimated pollutant exposures, exercise conditions, and physiological/biological responses. The models will account for repeated measures, clustering within schools, and potential confounders (age, sex, asthma status, BMI, meteorological variables).

Key Contributions and Scope
This protocol outlines a study designed to generate the first evidence on the short-term respiratory and immunological impacts of air pollution exposure during physical activity in London school playgrounds.

• Design Strengths: The use of a randomized crossover design allows each child to serve as their own control, reducing inter-individual variability. The inclusion of 330 children across 10 schools provides sufficient statistical power to detect a 5% change in R5, a clinically relevant threshold.
• Ecological Validity: By conducting interventions during typical school hours in real-world playgrounds, the study enhances the relevance of findings to daily school life.
• Public Engagement: The study includes a commitment to providing free outreach workshops for schools using real-time air quality data to empower monitoring.

Results
As this document is a study protocol published as a preprint, it does not report experimental results, statistical findings, or final conclusions regarding the health effects of air pollution. The paper details the planned methodology, sample size calculations (targeting 90.21% power), and analysis strategies rather than empirical outcomes.

Significance and Claims
The authors position the CHERISH study as a critical step in addressing an evidence gap regarding the interaction between physical activity and air pollution in children. The study claims significance in three main areas:

1. Scientific Evidence: It will provide the first direct comparison of acute health effects (lung function and airway inflammation) between active and sedentary exposures in school playgrounds.
2. Policy and Guidance: Findings are intended to support future public health guidance, school policy, and urban design strategies that promote active play while mitigating pollution risks.
3. Clinical Advice: The results aim to inform clinical advice for parents and healthcare professionals, particularly regarding children with asthma and other respiratory conditions, helping to determine whether the immediate benefits of exercise outweigh the transient risks of increased pollutant uptake in polluted environments.

The study is registered at clinicaltrials.gov (NCT07431021) and has received ethical approval from the Queen Mary Ethics of Research Committee. The authors emphasize that the study examines short-term responses only and cannot determine long-term health impacts.