Friday, January 10, 2014

What is the Risk of a Stroke from Long Term Exposure to Particulate Matter ?

Fine Particulate Air Pollution and the Progression of Carotid Intima-Medial Thickness: A Prospective Cohort Study from the Multi-Ethnic Study of Atherosclerosis and Air Pollution (9 page pdf, Sara D. Adar, Lianne Sheppard, Sverre Vedal, Joseph F. Polak, Paul D. Sampson, Ana V. Diez Roux, Matthew Budoff, David R. Jacobs, Jr., R. Graham Barr, Karol Watson, Joel D. Kaufman, PLOS Medecine, Apr. 23, 2013)

Also discussed here: Air Pollution as a Heart Threat (Deborah Blum, New York Times Poison Pen blog, Nov. 15, 20)

And here: Evolution of Air Pollution Monitoring in Ottawa (Natty Urquizo, 60 slides PowerPoint, Upwind-Downwind Conference, Hamilton, Feb. 23, 2012)

Today we review research into the health impact of long term (10 years) exposure to particulate matter and how this affects the thickening of arterial walls [intima-medial thickness]and heart disease through atherosclerosis. Results indicate that an increase of PM 2.5 mg/m3 is associated with a 2% relative increase in strokes and is evident at the neighbourhood level. This is significant because it expands the impact of PM from the known impact of short term exposure to long term. It also suggests that neighbourhoods located near higher levels of PM (such as proximity to vehicle emissions from traffic) would have higher mortality. Studies (such as from the City of Ottawa) show that many urban areas have more than 50% of vulnerable populations living within 50 m of busy roads and are at and strokesproximity to roads ottawa  

Key Quotes:  

“The Multi-Ethnic Study of Atherosclerosis and Air Pollution (MESA Air) was designed to investigate associations between long term PM2.5 exposures and the progression of atherosclerosis over a10-y follow-up period using information from the large population-based MESA cohort who were without pre-existing cardiovascular disease at baseline”

“increased exposure to pollutants, after other factors are factored out, can be directly linked to narrowing of blood vessels and to a steady thickening of artery walls"

“In a large prospective cohort study of adults without pre-existing cardiovascular disease, we found evidence that individuals with higher long-term residential concentrations of PM2.5 experience a faster rate of IMT [intima-medial thickness] progression as compared to other people within the same metropolitan area.”

“higher long-term PM2.5 exposures may be associated with an acceleration of vascular pathologies over time. As such, they may help explain why epidemiological studies have repeatedly found much larger associations between mortality and chronic air pollution exposures than can be explained by short-term triggering of cardiovascular events alone.”

 “participants living in parts of town with 2.5 mg/m3 higher concentrations of PM2.5 would have a 2% relative increase risk in stroke as compared to persons in a less polluted part of the metropolitan area.”

“these results for IMT in the first three exams of a large, multi-center, population-based cohort study support the hypothesis that PM2.5 may be associated with the progression of atherosclerosis, even at levels below existing regulatory standards. Such a pathway would lend further support to reported associations between air pollution and the incidence of clinical cardiovascular disease.”
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