Bans on smoking in public and the workplace have led to a 10 per cent drop in premature births and in emergency asthma treatment for children, researchers say.

The evidence, based on the records of more than two million children, comes from 11 published investigations into the impact of local or country-wide smoking bans in the US, Canada and four European countries.

Within a year of a ban being imposed, rates of pre-term births and hospital treatment for childhood asthma each fell by more than a tenth, researchers said.

Premature births are associated with a low birthweight and health problems for the child later in life.

Previous research into the benefits of smoking bans have focused mainly on adults, but children are disproportionately affected by passive smoking because their developing lungs and immune systems are more easily irritated.

A previous study in 2011, of 192 countries, found that children account for more than a quarter of the annual toll of 600,000 deaths attributed to second-hand smoking.

The new investigation, published in The Lancet on Friday, covered more than 2.5 million births and 250,000 hospital admissions of children who suffered an asthma attack.

The data was for the period 2008-2013.

“Our research shows that smoking bans are an effective way to protect the health of our children,” said Jasper Been of the University of Edinburgh’s Centre for Population Health Sciences in Scotland.

“These findings should help to accelerate the introduction of anti-smoking legislation in areas not currently protected.”

In a comment, smoking experts Sara Kalkhoran and Stanton Glantz at the University of California in San Francisco said the figures showed, among other things, that smoking bans pay for themselves.

“Medical expenses for asthma exceeded $US50 billion ($A54.13 billion) in the USA in 2007 and $US20 billion in Europe in 2006,” they said.

“If asthma emergency department visits and admissions to hospital decreased by even 10 per cent, the savings in the USA and Europe together would be $US7 billion annually.”

A 2012 analysis found a 15 per cent reduction in heart attacks and strokes and a 24 per cent drop in hospital admissions for respiratory disease after anti-tobacco laws were passed.

AFP