Significant reductions in air pollution over the past decade have improved life expectancy across various US counties, report researchers, although they stress that optimum air quality levels have not yet been reached.
"Despite the fact that the US population as a whole is exposed to much lower levels of air pollution than 30 years ago - because of great strides made to reduce people's exposure - it appears that further reductions in air pollution levels would continue to benefit public health," said lead author Andrew Correia (Harvard School of Public Health, Boston, Massachusetts, USA) in a press statement.
The researchers collected data on average yearly levels of fine particulate matter (PM2.5) measured in 545 US counties between 2000 and 2007 and calculated the mean life expectancy change associated with levels of air pollution in these areas, after adjusting for potential confounders such as smoking prevalence and socioeconomic status.
They estimated that a decrease in PM2.5 of 10 µg/m3 was linked to a mean increase in life expectancy of 0.35 years, with a stronger association seen in counties that were more urban and densely populated.
Women also seemed to benefit more from lower levels of air pollution, gaining 0.59 years for every 10 µg/m3 drop in PM2.5 compared with only 0.08 years for men.
Over the 2000 to 2007 period, the average life expectancy increased by 0.84 years and the mean PM2.5 level decreased by 1.56 µg/m3.
"Although PM2.5 reductions presumably account for some of the improvements in life expectancy over this period, it is only one of many contributing factors," explain Correia and colleagues in Epidemiology.
Previous studies have shown that reductions in the level of air pollution lower cardiovascular and pulmonary disease and mortality. Levels of PM2.5 have dropped significantly since 1980, but the rate of decline has slowed considerably since 2000.
The results from this study show that even the smaller decreases that have occurred since then have still had a beneficial effect on public health and could continue to do so, the researchers reason.
"Since the 1970s, enactment of increasingly stringent air quality controls has led to improvements in ambient air quality in the United States at costs that the US Environmental Protection Agency has estimated as high as [US]$ 25 billion per year. However, the extent to which more recent regulatory actions have benefited public health remains in question. This study provides strong and compelling evidence that continuing to reduce ambient levels of PM2.5 prolongs life," concluded senior co-author Francesca Dominici, also from the Harvard School of Public Health.
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