London's Ultra Low Emission Zone Linked to Improved Children's Lung Development, Lancet Public Health Study

Original publisher: The Conversation. A Lancet Public Health study followed 3,414 children over five years to test whether London's ultra low emission zone translated into health benefits. London children showed faster NO2 declines and greater FEV1 gains than a comparison group in Luton, with the gap in FEV1 essentially closed by the end of follow-up. FVC improvements lagged, suggesting different recovery dynamics. The study provides real-world evidence that cleaner air can support healthier lung growth, while noting the natural-experiment design cannot prove causation.

• ULEZ linked to faster NO2 reductions and faster FEV1 growth
• End-follow-up FEV1 gap closed, improving relative respiratory health
• FVC recovery remained incomplete, hinting at structural-lung differences
• As observational evidence, causation is plausible but not guaranteed

Context and Study Design

The Lancet Public Health study investigates whether London’s ultra low emission zone (ULEZ), introduced in 2019, translated into measurable health benefits. The researchers recruited 3,414 children aged six to nine in 2018 and followed them for five years. About 1,664 lived in central London where the ULEZ operated, while 1,750 resided in Luton, a comparable urban area without a clean air zone. The team compared baseline air pollution exposure and lung function, then tracked changes after the policy’s implementation. Lung function was assessed with non-invasive tests, including FEV1, a key measure of how much air a person can exhale in one second. Residential NO2 exposure was modeled to relate pollution to lung development. The Lancet Public Health article DOI is 10.1016/S2468-2667(26)00163-5.

Key Findings: Pollution Reduction and Lung Growth

At the start of the study, London children exhibited higher exposure to air pollutants and lower lung function than the Lutonians. Following the ULEZ introduction, London showed a substantially faster decline in NO2 levels compared with Luton. The authors report that nitrogen dioxide fell by 3.77 µg/m3 per year in London vs 1.77 µg/m3 per year in Luton. Concurrently, London children experienced a faster annual increase in FEV1, approximately 10 mL per year greater than Luton children. While the numerical gains may appear modest, they accumulate across childhood and can meaningfully influence long-term respiratory health. By the end of follow-up, the London and Luton cohorts had essentially the same average FEV1, and the proportion of clinically low FEV1 declined more in London (from 14% to 8.8%) than in Luton (from 8.9% to 6.9%).

Lung Function Details: FEV1 and FVC

In addition to FEV1, the study examined forced vital capacity (FVC), reflecting overall lung volume. At baseline, London children had about 55 mL lower FVC than their Lutonians. Over the follow-up period, London children’s FVC rose faster, narrowing the gap but not eliminating it. By the end of the study, London children still averaged roughly 25 mL lower FVC than those in Luton. The authors explain that this divergence may relate to how FVC more closely reflects structural lung growth, which could take longer to respond to cleaner air conditions compared with FEV1, a measure more sensitive to airway function fluctuations.

Interpreting the Mechanism and Implications

The authors emphasize a plausible mechanism: long-term exposure to NO2 and fine particulate matter is associated with poorer lung function and slower growth across childhood. Although all pollutants showed negative associations, NO2 had the clearest link, consistent with its close ties to road traffic emissions—the target of ULEZ. The study design positions the ULEZ as a real-world intervention rather than a randomized trial, so while causation cannot be proven, the timing of pollution reductions and lung growth patterns around the investment in cleaner air makes a causal interpretation plausible.

Limitations and Causality

The researchers are cautious about claiming that ULEZ caused the observed improvements. London and Luton are not identical, and the exposure estimates relied on residential models that do not capture non-residential exposures such as school time, commuting, or indoor environments. The COVID-19 pandemic also disrupted school follow-up, although sensitivity analyses suggested the main results remained robust. The authors acknowledge that a randomised design would be needed for definitive proof of causation, but contend that the convergence of evidence supports cleaner air as a contributor to healthier lung development in children.

Policy and Equity Implications

The broader message is that transport policy acts as health policy. Clean air zones should be designed with fairness and equity in mind, supporting low-income groups and individuals reliant on vehicles. The article notes that the heaviest pollution burden often falls on communities not primarily responsible for emissions, raising important questions about how to protect vulnerable populations in dense urban settings. The authors advocate careful evaluation of ULEZ as a public health intervention and suggest it may already be delivering benefits, reinforcing the view that reducing traffic-related pollution can support healthier lung growth in children.

Conclusion

Cleaner air from transport policy, the authors conclude, can contribute to healthier childhood lung development. While not a perfect causal study, the alignment of pollutant trends, the timing of policy implementation, and observed lung growth patterns indicate that ULEZ may be a valuable investment in public health as well as environmental policy.

Source: The Lancet Public Health, DOI 10.1016/S2468-2667(26)00163-5; original context discussed in The Conversation.