A study based at the University of Southern California (USC) tracked the health of almost 23,000 people from 260 Los Angeles neighbourhoods and found huge variations while suggesting the overall picture was far bleaker than previously suspected.

Due to the large scope of the study and sheer number of people interviewed and examined, the researchers were able to go deeper than predecessors and rule out many other factors which may have affected health and draw a detailed picture of the harm done by particulate pollution.

Their conclusion was that the death toll from fine particles could be up to three times greater than previously thought.

The epidemiologists examined links between particle pollution and mortality within more than 260 Los Angeles neighbourhoods.

Experts may be significantly underestimating air pollution’s role in causing early death, according to a team of American and Canadian researchers, who studied two decades’ worth of data on residents of the Los Angeles metro area.

For each increase of 10 micrograms per cubic metre of fine particles in a neighbourhood’s air the risk of death rose by 11 to 17 percent, said Michael Jerrett, associate professor of preventive medicine in the Keck School of Medicine of USC and the paper’s lead author.

Fine particle levels can differ by about 20 µg/m3 from the cleanest parts of Los Angeles to the most polluted, leading to huge differences in life expectancy.

“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 vast number of participants allowed scientists to control for dozens of factors that influence health outcome, such as smoking, diet and education.

When considering air pollution, the epidemiologists specifically looked at levels of particulate matter, a mixture of airborne microscopic solids and liquid droplets including acid, organic chemicals, metals, dust and allergens.

Microscopic particles less than 2.5 micrometres (PM2.5) in diameter pose the greatest problems to health because they can penetrate deep into the lungs and sometimes even enter the bloodstream.

Particulates are often found in smoke, vehicle exhaust, industrial emissions and haze, driven by the burning of fossil fuels.

Scientists also tracked ozone pollution, but found no link between ozone levels and mortality.

Researchers also linked pollution to diabetes, recording more than a twofold increased risk of death from the condition in highly polluted areas, but due to the small numbers of diabetes-related deaths overall they accept these findings are less reliable than those relating to heart disease.

“People who are diabetic may be more susceptible to day-to-day fluctuations in air pollution,” said Dr Jerrett.

“They may experience a state of greater inflammation – related to insulin resistance – that makes their lungs more receptive to receiving harmful particles.”

Researchers now plan to conduct a similar study in New York to try to duplicate findings.

“These findings should give us some pause to think about what we need to do as a society,” Jerrett said.

“Restrictions on tailpipe emissions have gotten tighter, but there are more trucks and cars on the roads and people are driving farther.

“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.”

By Sam Bond

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