Next time you go for a jog with traffic roaring past, spare a thought for your kidneys. A US-based study has found that breathing fine particles of pollution – such as those found in car exhaust – increases the risk of developing kidney disease.
The World Health Organisation estimates that air pollution is responsible for around seven million premature deaths globally each year, and links to a raft of health problems, from asthma and chronic lung disease to cardiovascular disease and stroke.
Researchers have had inklings that air pollution might damage kidneys, too. Coal mining communities often suffer higher rates of kidney disease, and lab mice forced to breathe exhaust particles bear the telltale signs of kidney damage.
The new study, led by Ziyad Al-Aly of the Veterans Affairs Saint Louis Health Care System, followed the health of nearly 2.5 million armed forces veterans for more than eight years. It provides the clearest evidence yet that, even at low levels, air pollution is bad news for kidneys.
The research, published in the Journal of the American Society of Nephrology, pairs the medical records of 2,482,737 mostly male armed forces veterans across the US to records of fine particulate pollution measured by Environmental Protection Agency (EPA) ground-based air monitoring stations.
Kidney health in veterans living in the dirtiest air during the study period fared the worst. And there was a clear linear relationship between pollution levels and kidney disease – the worse the air quality, the worse the outcomes.
For every increase of 10 micrograms of fine particulates per cubic metre of air, the risk of chronic kidney disease increased by 27%, and the risk of kidney failure increased by 26%.
The team then ran a second analysis, using air pollution data collected by two of NASA’s orbiting satellites, Aqua and Terra, to confirm the link.
The associations held: the greater the fine particulate pollution, the greater the chance of developing chronic kidney disease, and of that disease worsening.
Perhaps most concerning was that even at low levels of pollution – lower than the EPA’s recommended limit of 12 micrograms per cubic metre – kidney damage was evident.
“The message is that no level of air pollution is really safe,” says Al-Aly.
The team calculated that a staggering 337,032 cases of chronic kidney disease and 13,537 cases of kidney failure in the US could be attributed to particulate air pollution. Adhering to the EPA’s limit could avert 44,793 chronic kidney disease and 2,438 kidney failure cases each year.
“It’s an incredibly careful analysis,” says Vlado Perkovic, a kidney specialist at the George Institute for Global Health in Sydney, Australia, who was not involved in the study.
“These findings are going to have huge public health relevance,” he adds.
Xin Xu, a nephrologist from the Southern Medical University in Guangzhou, China, agrees. “I think it’s a very important piece of work,” he says, adding weight to his own work showing that in China – where he says pollution is severe – kidney damage worsens in people exposed to high levels of air pollution.
The results could also help to explain why some people who have none of the typical precursors to kidney disease – such as diabetes and hypertension – nonetheless develop the condition.
Scientists will now try to understand how pollution might cause kidney damage. Small particles f gold inhaled into the lungs make their way into the blood and are then filtered out by the kidneys, ending up in urine. Air pollution particles likely follow a similar route, but if toxic, could cause inflammation and oxidative stress to kidney tissues as they pass through.
They findings could also prompt policy makers to reassess their recommended safe levels of pollution. “The lower the better,” says Al-Aly.