Systematic review and meta-analysis on short-term concentrations of ambient ultrafine particles and natural, cardiovascular and respiratory mortality

BACKGROUND: Ambient ultrafine particles (UFP, <100 nm) are suspected to cause adverse health effects independent from larger particle fractions. Accordingly, there is increasing interest in their health effects. This paper describes a systematic review and meta-analysis of studies investigating the association of short-term concentrations of UFP with natural, cardiovascular, and respiratory mortality. METHODS: We systematically searched for epidemiological studies published between January 2011 and December 2024 in the databases PubMed and LUDOK and added studies from before 2011 from a previous review. We assessed heterogeneity and risk of bias and performed random-effects meta-analyses when at least four estimates were available. RESULTS: increase in UFP at lag 0, which had most available estimates. Overall, associations were non-significant and close to null across most lags. We found heterogeneity in UFP monitoring and lag reporting. CONCLUSION: The number of studies on the association between short-term UFP concentrations and mortality has increased substantially in the last years. However, the current evidence does not clearly support an association between short-term concentrations of UFP and mortality. Future studies should improve and harmonize UFP monitoring to improve investigation of health effects and inform policymaking.