Lung cancer burden attributable to ambient particulate matter: a nationally representative population-based case-control study

Background
Particulate matter with a diameter of 2.5 micrometers or less (PM_2.5) is a known lung carcinogen, but its impact in low-pollution settings is less understood. We assessed the association between long-term PM_2.5 exposure and lung cancer risk in Northern Ireland (NI), a region with relatively low air pollution levels.

Methods
We conducted a population-based case-control study using data from the Northern Ireland Cancer Registry and the Northern Ireland Cohort for the Longitudinal Study of Ageing. The study included 917 lung cancer cases diagnosed in 2014 and 8,088 controls without lung cancer. Eight-year average PM_2.5 exposure was estimated by linking residential postcodes to 1 km² resolution pollution maps. Fully adjusted logistic regression models were used, controlling for key confounders including smoking status and deprivation index to estimate odds ratios (ORs) and their 95% confidence intervals (95% CI), and population attributable fractions (PAFs).

Results
Individuals in the highest PM_2.5 tertile (>9.6 µg/m³) had a 37% increased lung cancer risk (OR: 1.37; 95% CI: 1.12–1.68) compared to the lowest tertile (<7.4 µg/m³). The association was stronger in women (OR: 1.79; 95% CI: 1.32–2.44) and not detected in men. Exposure above 10 µg/m³ accounted for 10% of cases, approximately 137 preventable lung cancers annually.

Discussion
Even in low-pollution regions, PM_2.5 contributes to lung cancer risk, especially in women. Strengthened air quality measures are needed to reduce preventable disease.