Living in a neighbourhood with noisy road traffic may reduce life expectancy and boost the risk of stroke, doctors reported in a study on Wednesday.

Researchers compared noise levels and data for deaths and hospital admissions across London, they said in a paper published in the European Heart Journal.

In places where daytime road traffic noise exceeded 60 decibels, there were four percent more deaths than in quieter areas where the noise was 55 decibels or below.

The World Health Organization (WHO) sets 55 decibels as the threshold of community noise beyond which health problems are possible.

Residents of noisier areas were also five percent likelier to be admitted to hospital with a stroke -- a figure that rose to nine percent among the elderly.

Significant night-time noise from road traffic, ranging from 55 to 60 decibels, was also linked to a five-percent increased stroke risk, but only among the elderly.

The paper took into account factors such as smoking habits, socio-economic status and ethnicity.

The survey, led by Jaana Halonen from the London School of Hygiene and Tropical Medicine, covered districts within the M25 motorway which rings the British capital. The study spanned 2003-2010.

More than 1.6 out of London's 8.6 million inhabitants are exposed to daytime traffic with noise above 55 decibels, it found.

Outside commentators said the increased health risk was small but clear.

The findings match other research showing that noise increases blood pressure and stress, which are contributors to cardiovascular disease, they said.

"Public-health policies must pay more attention to this emerging evidence," Francesco Cappuccio, a professor of cardiovascular medicine at the University of Warwick, told Britain's Science Media Centre.