(Reuters Health) - Breathing dirty air may increase the risk for kidney problems, a study in U.S. veterans suggests.

“Air pollution is a risk factor for kidney disease development,” Dr. Ziyad Al-Aly of the Veterans Affairs St. Louis Health Care System in St. Louis, Missouri, who helped conduct the research, told Reuters Health by phone. “You can argue that it’s even more of a problem in countries like China or India, where pollution is much, much, much worse.”

Dr. Al-Aly and his team studied particulate matter (PM), tiny fragments produced by fossil fuel combustion and other industrial processes, that can be inhaled deep into the lungs. High levels of PM 2.5 - meaning particles smaller than 2.5 micrometers across - are associated with heart disease, stroke, diabetes and a shorter life span.

To investigate whether PM might harm the kidneys as well, the researchers looked at more than eight years’ worth of data on nearly 2.5 million military veterans, using county-by-county pollution data from the Environmental Protection Agency (EPA). Vets living in counties with the highest PM levels were more likely to be African-American and to have high blood pressure and diabetes - both of which are also risk factors for kidney disease - as well as heart disease.

The risk that the veterans’ kidney function would worsen over time rose in tandem with the level of pollution they were exposed to at the study’s outset. Higher PM concentrations in the air were also associated with an increased risk of end-stage renal disease, in which the kidney can no longer filter blood effectively and a person requires dialysis to stay alive.

When Dr. Al-Aly and his colleagues repeated the analysis using National Aeronautics and Space Administration satellite pollution data, the results were consistent.

Nearly 45,000 new cases of kidney disease are diagnosed each year in the U.S., and it’s possible that some of those might be due to PM 2.5 pollution that exceeds EPA standards, according to the researchers. But even levels well below the EPA threshold are associated with significant risk, Dr. Al-Aly said.

The study wasn’t a controlled experiment, so it can’t prove that air pollution actually caused the kidney problems. Some other health- or lifestyle-related factors might be to blame.

Still, Dr. Aly-Aly said, studies in animals have shown that particles breathed into the lungs can reach the kidneys via the bloodstream, causing inflammation and oxidative stress within the blood-filtering organs.

Dr. Jennifer Bregg-Gresham of the Kidney Epidemiology and Cost Center at the University of Michigan in Ann Arbor reviewed the research for Reuters Health. “It has been known for a while that air pollution increases the risks for heart and lung problems. These new findings support that even low levels of fine particulate matter air pollution across the US can increase the risk of serious kidney problems,” she told Reuters Health in a telephone interview. “Given the millions of people with and at-risk for kidney disease who are impacted by air pollution, this has serious public health implications.”

She noted that people can reduce their personal exposure to PM air pollution with indoor air filtration and, in heavily polluted cities, wearing a validated respirator N95 facemask. Both measures can also reduce blood pressure, Dr. Bregg-Gresham added.

“Unfortunately, as of yet there have been no large scale studies proving that these measures can prevent actual heart, lung or other adverse health effects (like kidney disease). As such, for the time being each person needs to have a discussion with their health care provider about using these measures and if they may be warranted for them based upon their health status and risks of exposure,” she said.

“Air pollution is bad for everyone. Those that are frail or have known chronic diseases are the most vulnerable, in general. This study adds to the literature in the field and further promotes the case for lowering air pollution levels beyond even current standards, for its larger societal benefit, especially for at risk populations, and supports continued research in this area.”

SOURCE: bit.ly/2xyjeFE Journal of the American Society of Nephrology, online September 21, 2017.