Los Angeles has done much in recent
years to curb its notorious smog problem, but new research
shows its people continue to suffer a health hangover.
This study, in the November issue
of the journal Epidemiology, finds that we had
sorely underestimated air pollution's role in causing
early death. The authors found chronic health effects
of airborne particles are two to three times greater
than previously believed.
"We have convincing evidence that
those causes of death that we might expect from inflammation,
ischemic heart disease and lung disorders, are elevated
in areas of higher pollution levels," said lead author
Michael Jerrett, associate professor of preventive medicine
at the University of Southern California.
Twenty years of health records
from 23,000 LA residents suggested that each increase
of 10 micrograms per cubic metre (xg/m3)
of fine particles in a neighbourhood's air raised all-cause
mortality among participants by 11 to 17%, and mortality
from ischemic heart disease by 25 to 39%.
The researchers followed 22,906
participants in the American Cancer Society's Cancer
Prevention Study II, which ran from 1982 to 2000, by
which time 5,856 had died. Their health outcomes were
compared to pollution measurements taken over the years
by nearly seventy monitoring devices spread around the
city, which provided a detailed picture of pollution
in each of 267 zip codes. The final analysis controlled
for individual risk factors like smoking, diet and educational
level.
NOT
JUST BLOWING SMOKE
"By looking at the effects of pollution within communities,
not only did we observe pollution's influence on overall
mortality, but we saw specific links between particulate
matter and death from ischemic heart disease, such as
heart attack, as well as lung cancers," said Dr Jerrett.
The pollutants measured were all
particles smaller than 2.5 micrometres in diameter.
These "PM2.5" particles pose the greatest health risk,
as they can easily enter the lung and in some cases
the bloodstream. Within Los Angeles, local levels can
vary by as much as 20 xg/m3,
enough to produce significant differences in mortality
according to these findings.
Car exhaust fumes are prime culprits,
Dr Jerrett says. "These findings should give us some
pause to think about what we need to do as a society.
Restrictions on tailpipe emissions have gotten tighter,
but there are more trucks and cars on the roads and
people are driving farther." He adds, "This study may
cause us to reflect on how we use our cars, what cars
we drive and whether we can do anything to make tailpipe
emissions from all vehicles less harmful to health."
OZONE
OFF THE HOOK
But despite the emphasis on cars, one automobile by-product
is exonerated. Ozone levels were also measured by the
researchers, but surprisingly, proved to have no influence
on health outcomes.
The study was supported by the
National Institute of Environmental Health Sciences,
which is also behind another study of LA pollution in
the same issue of Epidemiology. Researchers looked
at the link between pollution and asthma in 208 children
who were part of the Children's Health Study, which
has tracked children's respiratory health since 1993.
DON'T
PLAY NEAR TRAFFIC
Looking at data from 10 California cities, researchers
found that proximity to a freeway was directly correlated
to nitrogen dioxide levels, which in turn translated
to higher asthma risk. For each increase of 5.7 parts
per billion in average NO2
— about the gap between the cleanest and most polluted
areas in the study — the risk of asthma increased
by 83%. And for every 1.2 kilometres closer the students
lived to the freeway, asthma risk went up by 89%.
"These results have both scientific
and public health implications," said Dr David Schwartz,
director of the National Institute of Environmental
Health Sciences. "They strengthen an emerging body of
evidence that air pollution can cause asthma, and that
exposure to outdoor levels of nitrogen dioxide and other
traffic-related air pollutants may be a significant
risk factor for this illness."
Lead author Dr James Gauderman
echoed the sentiments of his USC colleague Dr Jerrett.
"Considering the enormous costs associated with childhood
asthma, today's public policy toward regulating pollutants
may merit some re-evaluation."
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