An international team of health experts, hygienists, pollution specialists and biostatisticians has found, via systematic review of almost 200 studies on air pollution, a strong positive association between long-term exposure to traffic pollution and an increase in death rates.
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In their paper published in the journal Environment International, the group describes how they approached their analyses and what they learned.
"The Panel used a systematic approach to conduct the review. An extensive search was conducted of literature published between 1980 and 2019.
"A new exposure framework was developed to determine whether a study was sufficiently specific to TRAP, which included studies beyond the near-roadway environment.
"We performed random-effects meta-analysis when at least three estimates were available of an association between a specific exposure and outcome.
"We evaluated confidence in the evidence using a modified Office of Health Assessment and Translation (OHAT) approach, supplemented with a broader narrative synthesis.
"Thirty-six cohort studies were included. Virtually all studies adjusted for a large number of individual and area-level covariates—including smoking, body mass index, and individual and area-level socioeconomic status—and were judged at a low or moderate risk for bias. Most studies were conducted in North America and Europe, and a few were based in Asia and Australia.
"The meta-analytic summary estimates for nitrogen dioxide, elemental carbon and fine particulate matter—pollutants with more than 10 studies—were 1.04 (95% CI 1.01, 1.06), 1.02 (1.00, 1.04) and 1.03 (1.01, 1.05) per 10, 1 and 5 µg/m3, respectively.
"Effect estimates are interpreted as the relative risk of mortality when the exposure differs with the selected increment. The confidence in the evidence for these pollutants was judged as high, because of upgrades for monotonic exposure-response and consistency across populations. The consistent findings across geographical regions, exposure assessment methods and confounder adjustment resulted in a high confidence rating using a narrative approach as well.
"The overall confidence in the evidence for a positive association between long-term exposure to TRAP and non-accidental mortality was high." ■