The review pooled 19 observational studies of ambient particulate matter and venous thromboembolism covering over 4.5 million participants, harmonising estimates to increments of 10 micrograms per cubic metre. Overall long-term associations were not significant for PM2.5 (HR 1.42, 95% CI 0.88-2.28) or PM10 (HR 1.18, 0.85-1.64), both with heterogeneity above 96%. Restricting to studies that natively reported in those units gave PM2.5 a hazard ratio of 1.07 (1.01-1.14) with no heterogeneity at all, and short-term exposures showed no association.
Why it is interesting: The result turns on how exposures were harmonised rather than on the underlying data, which is a caution about how air pollution estimates are assembled.