Older adults are more likely to die on days when air pollution rises, even when contaminant levels are below the limit considered safe by US regulators, a new study suggests.
Researchers looked at 22mn deaths nationwide to see if there was any connection between fatalities and fluctuations in daily concentrations of ozone, an unstable form of oxygen produced when pollution reacts with sunlight, and so-called PM 2.5, tiny particles that include dust, dirt, soot and smoke.
Most of the deaths in the study occurred on days when ozone and PM 2.5 levels were below the limits set by the US Environmental Protection Agency (EPA).
Previous studies have linked air pollution to an increased risk of chronic health problems and premature death, but those studies focused on cities, said study co-author Joel Schwartz of the Harvard TH Chan School of Public Health in Boston.
The study focused on deaths from 2000 to 2012 for people in more than 39,000 ZIP codes nationwide who were insured by Medicare, the US health programme for the elderly and disabled.
Researchers compared satellite data on daily PM 2.5 and ozone levels on the days people died in specific ZIP codes to air quality levels on another day within a week or two of each fatality.
EPA standards cap 24-hour PM 2.5 at 35 micrograms per cubic meter of air (ug/m3) and 8-hour ozone at 70 parts per billion (ppb).
During all of the days examined in the study, 94% had PM 2.5 levels below 25 ug/m3, and 95% of the deaths occurred on these days, the study found.
At the same time, 91% of the days examined had ozone levels below 60 ppb, and 93% of the deaths occurred on these days.
Even when air quality still met EPA standards, each 10 ug/m3 daily increase in PM 2.5 levels was associated with an increase of 1.42 deaths per day for every million people, the researchers report in the Journal of the American Medical Association.