Nitrogen dioxide exposure and lung cancer risk in non-European countries: a systematic review and meta-analysis of the decades 2014-2024

Background Lung cancer remains a leading cause of incidence and mortality worldwide, with nitrogen dioxide (NO 2 ) as a potential risk factor. While European studies have shown a positive association between NO 2 exposure and lung cancer risk, evidence from non-European regions is limited. Methodology This systematic review and meta-analysis of 11 cohort studies comprising 68,367,056 participants, identified from Google Scholar, PubMed, and Science Direct up to June 6, 2024, was performed to evaluate the impact of NO 2 on the risk of lung cancer beyond Europe. Studies were selected on the basis of predefined criteria, and the risk of bias was assessed via the Newcastle-Ottawa Scale (NOS). Hazard ratios (HRs) were standardized to 10 parts per billion (ppb) increase in NO 2 . Results The pooled HR represents the change in lung cancer risk per 10 ppb increase in NO 2 exposure. Overall, NO 2 exposure was significantly associated with increased lung cancer risk (pooled HR: 1.08, 95% CI: 1.03-1.13). Subgroup analyses revealed significant associations with lung cancer incidence (HR: 1.06, 95% CI: 1.01-1.12) and mortality (HR: 1.13, 95% CI: 1.01-1.26). Smoking-specific analyses were not statistically significant among smokers (HR = 1.06; 95% CI: 0.98-1.15) or non-smokers (HR = 0.96; 95% CI: 0.86-1.08). Regional variations included significant associations in America (HR: 1.06, 95% CI: 1.02-1.11) but not in Asia (HR: 1.22, 95% CI: 0.96-1.55). Limitations include evidence gaps between low-income countries and regional differences. Conclusion In summary, this meta-analysis suggests that NO 2 exposure is associated with an increased risk of lung cancer beyond European countries. This study highlights the need for global air quality regulations and further research into the role of NO 2 in lung cancer.