A shared analysis of European populations
Beelen and colleagues analysed 22 cohorts comprising 367,251 people, with average follow-up of 13.9 years. They estimated annual outdoor pollution at residential addresses using land-use regression. The question was about long-term exposure and natural-cause mortality, not the effect of a single afternoon outside.
The PM2.5 result
Each 5 µg/m³ increase in estimated PM2.5 was associated with a hazard ratio of 1.07 for natural-cause mortality; the 95% confidence interval was 1.02–1.13. An association remained when analyses were restricted to participants below 25 or 20 µg/m³. Those historical cut-offs must not be described as current WHO guidelines.
Association and exposure uncertainty
Residential modelling cannot capture all personal exposure or changes in where people spend their time. The observational design also leaves room for residual confounding. A hazard ratio describes a comparison between groups over follow-up; it is not an absolute risk estimate for an individual.
A limit is not a guarantee of no risk
These results support taking lower exposure seriously even when a regulatory limit is met. They do not turn a current hourly concentration into a prediction of future disease. Always distinguish annual exposure, daily averages and short-term index readings when applying the finding.
Sources
Educational information; personal health questions belong with your clinician.
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