Short-term air pollution exposure increases heart attack risk
MedWire News: Short-term exposure to most major air pollutants, excluding ozone, increases a person's risk for myocardial infarction (MI), suggest results from a systematic review and meta-analysis.
"Since the 1990s, many epidemiological studies have demonstrated associations between air pollution levels and human health in terms of hospital admissions and overall mortality, including respiratory or cardiovascular mortality," say Hazrije Mustafić (INSERM, Paris, France) and colleagues.
"However, the association between air pollution and near-term risk of MI remains controversial," they add.
To investigate further, Mustafić and team analyzed data from 34 studies. To be included, the studies had to investigate the association between short-term (up to 7 days) exposure to air pollutants (general air pollution, ozone, carbon monoxide, nitrogen dioxide, sulfur dioxide, particulate matter [PM]10, and PM2.5) and MI or acute coronary syndrome (ACS) risk.
For each of the pollutant types, the researchers calculated the change in relative risk (RR) associated with a 10 µg/m3 increment or a 1 mg/m3 increment for carbon monoxide.
All of the air pollutants tested except ozone were associated with an increased risk for MI with increasing levels of exposure. The increases in RR for MI associated with exposure to one increment of carbon monoxide, nitrogen dioxide, sulfur dioxide, PM10, and PM2.5, were 4.8%, 1.1%, 1.0%, 0.6%, and 2.5%, respectively, all of which were statistically significant.
Depending on the pollutant, the population attributable fraction (PAF) of risk for MI associated with air pollution exposure ranged from 0.6% to 4.5%.
For ozone, the relative risk for MI was slightly increased with exposure to one increment, but not sufficiently to be statistically significant.
One potential cause of the increased risk for MI associated with air pollution could be inflammation, say the authors.
"Studies have shown that levels of inflammatory markers such as C-reactive protein are higher as a result of exposure to air pollution," they write in JAMA.
Other possibilities could be that air pollution exposure results in increased heart rate and decreased heart rate variability, or that such exposure results in increased blood viscosity and therefore increased thrombus risk.
"Although the RRs were relatively low, the PAFs were not negligible because the majority of the population is exposed to air pollution in industrialized countries," say Mustafić et al.
"Further research is needed to determine whether effective interventions that improve air quality are associated with a decreased incidence of MI," they conclude.
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By Helen Albert