New data suggest that pollution in the air may be associated with
increased risks for MI and stroke.
A review and meta-analysis of previous studies found that short-term
exposure (less than 7 days) to all major air pollutants, with the exception of
ozone, is significantly associated with an increased risk for MI. Researchers
in Paris reviewed 34 studies conducted between 1988 and 2011 that analyzed the
association between air pollutants and MI risk. Results showed that carbon
monoxide (RR=1.048; 95% CI, 1.026-1.070), nitrogen dioxide (RR=1.011; 95% CI,
1.006-1.016), sulfur dioxide (RR=1.010; 95% CI, 1.003-1.017), particulate
matter with an aerodynamic diameter of 10 mcm (PM10) or less
(RR=1.006; 95% CI, 1.002-1.009) and particulate matter with an aerodynamic
diameter of 2.5 mcm (PM2.5) or less (RR=1.025; 95% CI, 1.015-1.036)
were significantly associated with an increase in MI risk. However, ozone
pollutants (RR=1.003; 95% CI, 0.997-1.010) were not associated with an
increased risk. A subgroup analysis based on study quality showed similar
results to the overall analysis.
Gregory A. Wellenius
“Our meta-analysis is the first, to our knowledge, to evaluate the
quality and magnitude of associations between short-term exposure to major air
pollutants and the
risk of MI,” Hazrije Mustafic, MD, MPH, of the
University Paris Descartes, INSERUM Unit 970, Paris, and colleagues wrote in
the Journal of the American Medical Association. “Further research
is needed to determine whether effective interventions that improve air quality
are associated with a decreased incidence of MI.”
Pollutants and stroke risk
In other research, two studies published in Archives of Internal
Medicine report an association between air quality and risk for acute
ischemic stroke and cognitive decline in older women.
Gregory A. Wellenius, ScD, of Brown University, and colleagues
evaluated the association between changes in fine particular matter air
pollution (particulate matter <2.5 mcm/m3) levels and risk for
ischemic stroke. The study included more than 1,700 patients (mean age, 73
years) who were hospitalized at Beth Israel Deaconess Medical Center between
1999 and 2008. Risk for ischemic stroke onset and particulate matter levels in
the hours and days preceding each event were assessed. During the study period,
PM2.5 levels in the Boston area did not exceed current Environmental
Protection Agency Air Quality Index standards, the researchers noted.
On days classified as “moderate” by the EPA (particulate
matter <2.5 mcm/m3; PM2.5), risk for ischemic stroke
was 1.34 (95% CI, 1.13-1.58) compared with days classified as “good”
(particulate matter <15 mcm/m3). When researchers considered
particulate matter levels as a continuous variable, estimated OR of ischemic
stroke onset was 1.11 (95% CI, 1.03-1.20) per interquartile range increase in
particulate matter levels.
In a second study, Jennifer Weuve, MPH, ScD, of Rush University
Medical Center, and colleagues evaluated air pollution in relation to cognitive
decline in older women using a study population from the Nurses’ Health
Study Cognitive Cohort, which included more than 19,000 US women aged 70 to 81
“In this large, prospective study of older women, higher levels of
long-term exposure to both PM2.5-10 and PM2.5 were
associated with significantly faster
cognitive decline,” the researchers wrote.
Results showed a 20year decline on global cognitive function scores in
women with the highest levels of exposure to particulate matter levels. These
associations were present at levels of particulate matter exposure typical in
many areas of the United States, according to the researchers.
“Therefore, if our findings are confirmed in other research, air
pollution reduction is a potential means for reducing the future population
burden of age-related cognitive decline and, eventually, dementia,” Weuve
and colleagues concluded.
Burden of pollution on health
Inflammation, abnormal regulation of the cardiac autonomic system, and
increased blood viscosity and vasoconstrictors due to air pollution were
identified as possible mechanisms for the associations found in the study by
Mustafic and colleagues. However, the researchers acknowledged that these
associations are relatively small compared with associations of classic MI risk
factors such as smoking, hypertension or diabetes.
In an editorial published in JAMA, Robert D. Brook, MD, of
the University of Michigan, and Sanjay Rajagopalan, MD, of the Dorothy
M. Davis Heart and Lung Research Institute at Ohio State University Medical
Center, said these data should serve as a reminder that “clinical events
could be initiated by even briefer sub-daily periods of PM2.5
“With the availability of improving pollutant data, future studies
should aim to elucidate the health effects of sub-daily time windows of
exposure. If similar findings are corroborated or found for other diseases,
those who create air quality standards might need to consider the difficult
task of curbing sub-daily
particulate matter concentrations, as they did to create the
existing 8-hour ozone regulations,” Brook and Rajagopalan wrote.
In another commentary published in Archives of Internal Medicine,
Rajiv Bhatia, MD, MPH, of the San Francisco Department of Public Health,
said, “Improved control of human exposure to PM2.5 is
technically feasible but will require increased efforts to assess exposure at
the community level, more stringent and creative regulatory initiatives and
political support. Physicians, who are already responding to the human
consequences of particulate pollution, can be effective advocates for these
protections.”– by Katie Kalvaitis and Casey Murphy
For more information:
Disclosure: Drs. Bhatia, Brook, Mustafic, Rajagopalan, Wellenius
and Weuve report no relevant financial disclosures.