People who live close to major roads may have an increased risk of suffering from kidney problems, a new study suggests.

According to US scientists, impaired kidney function is a known risk factor for heart disease and stroke, so the findings could further explain why air pollution is so bad for the health of the heart.

The scientists looked at over 1,100 adults who had suffered a stroke over a five-year period. Half lived within 1km of a major road, while the remainder lived between one and 10km away.

On admission to hospital, each patient had their serum creatinine measured.

This is a byproduct of muscle metabolism, which is filtered out of the body by the kidneys. The rate at which this happens is known as the glomerular filtration rate (GFR) and this acts as an indicator of how well the kidneys are working - the higher the rate, the healthier the kidneys.

The study found that those who lived closest to major roads had the lowest GFR. The results stood even when other factors were taken into account such as age, gender, smoking and heart conditions.

The scientists noted that those who lived 50 metres away from a busy road had a GFR that would be expected to be found in someone who was four years older, compared to people who lived 1,000m from a busy road.

They also estimated that living just 50m away was linked to a 4% higher rate of heart-related death and a 1% increased rate of death from all causes compared to living 1,000m away.

The scientists from Boston said that traffic-related air pollution increases the risk of heart disease and stroke due to a number of reasons, including a narrowing of the arteries as a result of the build-up of plaque.

They pointed out that the kidneys are very susceptible to the build-up of arterial plaque and added that these results therefore imply ‘that exposures associated with living near a major roadway contribute to reduced renal function, an important risk factor for cardiovascular events'.

Details of these finding are published in the Journal of Epidemiology and Community Health.

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