Traffic pollution can harm the arteries that supply blood to the kidneys, a new study has warned.
Experts already know that long-term exposure to exhaust fumes increases the risk of vascular diseases such as heart attacks and stroke.
The study authors, Dr Murray Mittleman and colleagues at the Beth Israel Deaconess Medical Center in Boston, measured kidney function in 1,100 stroke patients using a recognised test called the glomerular filtration rate (GFR).
The GFR is an indicator of how well the kidneys are working. A low GFR suggests kidney problems.
Half of the stroke patients in the study lived within 1km of a major road in the Boston metropolitan region, and the rest lived between 1km and 10km away, BBC News reported.
Those patients who lived closest to a major road had the lowest GFR even after taking account of factors such as age, sex, race, smoking and other underlying medical conditions.
The difference in GFR between these patients and those who lived further away from traffic pollution was comparable to a reduction in GFR associated with being four years older, the researchers said.
"The importance of healthy kidneys is often overlooked, but many of the things that can damage the heart also affect these vital organs," Dr Tim Chico, a heart expert at the University of Sheffield in the UK, said.
"Many people are unaware of the close link between heart and kidney disease, but problems with one often lead to problems with the other," Chico said.
For instance, most people with kidney disease had high blood pressure, which increased risk of heart disease, while heart disease and its treatment frequently placed a strain on kidney function, he said.
However, Chico cautioned that the current study only showed a link - it does not prove living next to a road definitely affects kidney function.
The study researchers were unable to control for all socio-economic factors. They said more studies looking at different groups of people are needed to confirm the findings.
The study was published in the Journal of Epidemiology and Community Health.
