A new Harvard University study for the first time links hospitalizations for common blood, skin and kidney ailments to short-term exposure to fine particulate matter from fossil fuel combustion and wildfires.

The findings widen the population of older Americans considered especially vulnerable to threats from the air pollutant even when exposed to it over short periods.

Led by researchers at Harvard University's T.H. Chan School of Public Health, the study published Wednesday in the British medical journal BMJ found that short-term exposure to fine particulate matter led to higher levels of hospitalization for people with illnesses such as septicemia, or blood poisoning, kidney failure, urinary tract infections, skin and other tissue infections and electrolyte disorders often brought on by loss of fluids from vomiting or diarrhea.

Researchers defined "short-term" as exposure on the day of hospitalization and compared the pollution levels to the day before. The population studied was Americans over the age of 65, through a vast analysis of Medicare records for the 48 continental states.

As the amount of PM 2.5 increased between the days analyzed, so did the hospital admission rate connected to those disease groups. Further, the link between exposure to fine particulate matter and hospitalizations was still evident even when the daily air pollution levels were lower than current World Health Organization guidelines and the less-stringent U.S. regulatory standards.

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The researchers studied a microscopic pollutant known as PM 2.5, which is generated by fossil fuel combustion in power plants and vehicles and by wildfires.

The tiny particles infiltrate the lungs, contributing to heart disease and worsening respiratory conditions such as asthma over the long-term, studies have shown. A 2015 study by the World Health Organization estimated that regular exposure to outdoor PM 2.5 pollution caused 3.7 million premature deaths worldwide each year. Previous studies showed that exposure to PM 2.5 heightened the risk of hospitalization largely for cardiovascular and respiratory illnesses, diabetes and Parkinson's disease.

The new study indicates that people with diseases other than those with a clear link to heart or lung problems are also harmed by even short-term exposure to PM 2.5.

"The study shows that the health dangers and economic impacts of air pollution are significantly larger than previously understood," said Yaguang Wei, the study's lead author and a doctoral student at the Chan School.

Trump EPA Moves to Suppress Science on PM 2.5

The study's focus on a broader public vulnerability to PM 2.5 comes as the Trump administration prepares to adopt a regulation that would severely curtail the use of scientific research to support public health standards, a major step in its efforts to undo pollution rules.

Environmental Protection Agency Administrator Andrew Wheeler, a former coal industry lobbyist, has described the proposed rule as an effort to improve "transparency." But it has been widely criticized as an attempt to protect polluters by preventing policymakers from considering decades of well-established scientific research that connects air pollution to premature death.

The draft rule would prevent the use of studies based on confidential health data, which is often necessary to get a wide swath of participants and sensitive details. If it is also applied retroactively, that could lead to the regulator's rejection of a seminal 1993 Harvard study that showed the threat that air pollution, including PM 2.5, poses to human health.

That has triggered a backlash in the medical and scientific communities, which say the result would be increased harm to human health. On Tuesday, the executive editors of some of the world's most prestigious scientific journals, including Nature, Science and The Lancet, published a rare joint statement condemning the proposed rule. Scientists and health experts have been fighting it for over a year, raising alarms that it could be used to suppress scientific evidence critical for health regulations by preventing the use of studies useful for drug development or understanding asthma and pollution impacts. If such scientific evidence is dismissed by EPA under the new rule, "that would be a catastrophe," they wrote.

Francesca Dominici, a professor of biostatistics at the Chan school and the new study's principal investigator, described the proposed rule as "clearly an attack against science."

Understanding the Connections

The new Harvard PM 2.5 study has transparency built into its design—it used government data from Medicare which is accessible to others who might want to replicate or build off the research.

The study was partly funded by the EPA and arrives as the agency should start a process to review and finalize the National Ambient Air Quality standards, including on fine particulates, by the end of 2020. EPA staff have reached a preliminary conclusion that the current PM 2.5 standard is too weak, but the agency's Trump administration-appointed science advisers disagreed. The final decision will be Wheeler's.

For the study, researchers analyzed hospital admissions data from 2000 to 2012 for 95 million inpatient claims on Medicare.

They classified the illnesses that landed people in the hospital into 214 groups, based on codes Medicare uses. To estimate the daily PM 2.5 levels over the same period, the researchers relied on satellite-based pollution measurements and a computer model of air pollution. Then they matched the PM 2.5 estimates with the zip codes of those people hospitalized.

The study did not seek to determine how PM 2.5 worsens the illnesses for which people were hospitalized. Wei, the lead author, said that many studies have shown that exposure to fine particulate matter can induce inflammation. But for some of the diseases found to be aggravated by PM 2.5, the underlying mechanism of how exposure worsens illness wasn't clear and warranted further research.

"Now that we have reported on these new sets of diseases, it will allow others to look into the physiology of the diseases," Dominici said. "It will open up a better understanding of how this is happening and that will allow us to prevent these hospitalizations."

InsideClimate News reporter Marianne Lavelle contributed to this story.