Image caption The "free-coal" policy was in effect north of the Huai River in 1950-1980

China's policy of giving free coal for heating to residents in the north has contributed to shaving 5.5 years off life expectancy there, a study says.

It says air pollution from burning coal in the area north of the Huai River, with a population of some 500m people, was 55% higher than in the south.

The region also had higher rates of heart and lung disease as a result of the policy in force up to 1980.

The study was conducted by researchers from China, the US and Israel.

'Disastrous consequences'

They studied pollution and deaths in 90 cities in the north and south between 1981 and 2000.

They specifically looked at the increase in a type of pollution called total suspended particulates (TSPs) found in soot and smoke.

The researchers then analysed mortality statistics in 1991-2000 and found evidence of shorter life expectancy in the previously "free coal" areas.

"Life expectancies are about 5.5. years lower in the north owing to an increased incidence of cardio-respiratory mortality," said the study published in the Proceedings of the National Academy of Sciences.

"The analysis suggests that the Huai River policy, which had the laudable goal of providing indoor heat, had disastrous consequences for health."

The scientists argued that their findings may help other emerging economies - such as Brazil or India - to find better ways to combine a drive for economic growth and public health protection.

The report's findings will increase pressure on the Chinese authorities to do more to tackle pollution, the BBC's Martin Patience in Beijing reports.

Earlier this year, the government faced a public outcry after air pollution soared past levels considered hazardous by the World Health Organization, our correspondent says.