Short-term air pollution exposure ‘increases mortality risk’

A leading US has linked short-term exposure to fine particles and ozone – even at levels well below legal air pollution limits – to an increase in the number of premature deaths caused by air pollution in over 65s.

The study, from Harvard’s TH Chan School of Public Health was published last week (26 December) in the Journal of the American Medical Association (JAMA), and has led researchers to call for a review of air quality standards.

The Harvard study suggested that even short-term exposure to air pollutants can lead to increased mortality rates in over 65s

Studies have linked fine particles (PM2.5) and ozone with increased mortality rates over a long term period of exposure. This has contributed to the development of limits aiming to cut the risk of harm to human health caused by continued exposure to high levels of air pollution.

As part of the Harvard study, researchers assessed daily air pollution exposures using prediction models that provided estimates of PM2.5 and ozone for most of the US, including unmonitored areas.

This air pollution data was then linked with mortality data from the US federal health insurance programme for the over-65s – Medicare – in over 93% of all postal code areas across the US, over a 13-year period from 2000-2012.

Air pollution

During the study period, 22 million people in the study population died. Researchers found that, for each 10 µg/m3 daily increase in PM2.5 and 10 parts-per-billion (ppb) daily increase in ozone, the daily mortality rate increased by 1.05% and 0.51%, respectively.

According to the study’s authors, the public health impact could be vast if it is applied to the whole US population of seniors.

The researchers suggested that an increase of just 1 µg/m3 in daily PM2.5 exposure over the course of one summer in the US would lead to 550 extra deaths per year and 7,150 extra deaths over the course of the 13-year study period.

An increase of just 1 ppb in daily ozone over the summer would lead to 250 extra deaths per year or 3,250 extra deaths over 13 years, the study concluded.

Commenting on the findings, Francesca Dominici, professor of biostatistics, co-director of the Harvard Data Science Initiative, and senior author of the study, said: “This the most comprehensive study of short-term exposure to pollution and mortality to date. We found that the mortality rate increases almost linearly as air pollution increases. Any level of air pollution, no matter how low, is harmful to human health.”

Other Harvard Chan authors involved in the study included Lingzhen Dai, Yun Wang, Antonella Zanobetti, and Christine Choirat.

Findings of the study follow on from research published earlier in the year by Harvard Chan researchers which suggested that long-term exposure to air pollution was linked with an increased risk of premature death, even at levels below the national standards for long-term exposures.

The World Health Organisation recommends that exposure to a mean level of no more than 10 μg/m3 should be considered the safe level for human health.

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Harvard TH Chan School of Public Health