Results of an HEI Systematic Review on the Health Effects of Long-term Exposure to Traffic-Related Air Pollution

Abstract

BACKGROUND AND AIM: After a broad search, the HEI Panel on the Health Effects of Long–Term Exposure to Traffic–Related Air Pollution (TRAP) identified 1100 studies relevant for further screening, 352 of which met the inclusion criteria and are considered in the systematic review. Respiratory effects in children (N=117) and birth outcomes (N=86) were the most common outcomes published in the literature. Slightly fewer studies investigated cardiometabolic effects (N=57), respiratory effects in adults (N=50), and mortality (N=48). METHODS: The systematic review is undergoing independent peer-review and publication is aimed for late 2021. RESULTS:The Panel’s initial findings were for a moderate to high level of confidence in an association between exposure to TRAP with term low birth weight. They also reported a moderate or high level of confidence in an association between exposure to TRAP and asthma onset in children and adults, and occurrence of acute respiratory infections in children. Furthermore, they found moderate evidence for an association between exposure to TRAP and ischemic heart disease, stroke, and diabetes mellitus. The overall confidence in an association between TRAP exposure and mortality was high for all-cause, circulatory, ischemic heart disease mortality; moderate to high for lung cancer mortality; and moderate for respiratory mortality. For the other health outcomes assessed, the confidence was very low or low for an association with TRAP, and the evaluation was often limited by the small numbers of studies. CONCLUSIONS:In light of the large number of people exposed to TRAP – both in and beyond the near–road environment, the Panel concluded that the moderate to high confidence in an association between long-term exposure to TRAP and various adverse health effects indicates that exposures to TRAP are an important public health concern and deserve continued targeted policy and broader public focus. KEYWORDS: traffic-related air pollution, systematic review, birth outcomes, cardiometabolic effects, respiratory effects, mortality