Low level pollution within UK guidelines causes changes to the heart similar to those seen in the early stages of heart failure, a study has warned.

The findings were based on British volunteers who did not live in large cities but near loud, busy roads.

Road transport accounts for 20 to 30 per cent of outdoor air pollution in the UK.

Being exposed to levels of soot and harmful fumes at levels well within UK legal limits damages the heart and the more a person was exposed, the larger their hearts became.

Scientists are now urging the UK had to adopt stricter limits to air pollution as it is now the largest environmental risk factor linked to deaths in England.

The study was based on around 4,000 participants in the UK Biobank study who did not have underlying heart problems, or had recently moved. The volunteers had blood tests and health scans while a heart MRI measured the size, weight and function of their hearts at fixed times.

It found a clear association between those who lived near loud, busy roads and were exposed to nitrogen dioxide (NO2) or PM2.5 – small particles of air pollution – and the development of larger right and left ventricles in the heart.

The ventricles are important pumping chambers in the heart and, although these participants were healthy and had no symptoms, similar heart remodelling is seen in the early stages of heart failure.

Higher exposures to the pollutants were linked to more significant changes in the structure of the heart.

For every 1 extra μg per cubic metre of PM2.5 and for every 10 extra μg per cubic metre of NO2, the heart enlarges by approximately 1%.

The average annual exposures to PM2.5 (8-12μg per cubic metre) were well within UK guidelines (25μg per cubic metre), although they were approaching or past World Health Organisation (WHO) guidelines of 10μg per cubic metre.

Yet WHO has said that there are no safe limits of PM2.5.

The participants’ average exposure to NO2 (10-50μg per cubic metre) was approaching and above the equal WHO and UK annual average guidelines of 40μg per cubic metre.

Clinical Fellow Dr Nay Aung who led the data analysis from Queen Mary University of London said: “Although our study was observational and hasn’t yet shown a causal link, we saw significant changes in the heart, even at relatively low levels of air pollution exposure.

“Our future studies will include data from those living in inner cities using more in-depth measurements of heart function.”