* Preterm birth risk lower after each phase of smoking ban
* Findings suggest smoke-free laws have early health impact
* Other studies also found effect on asthma, heart attacks
By Kate Kelland
LONDON, Feb 15 (Reuters) - Banning smoking in enclosed public places can lead to lower rates of preterm birth, according to Belgian researchers who say the findings point to health benefits of smoke-free laws even in very early life.
It is well known that smoking during pregnancy can stunt the growth of unborn babies and shorten gestation, and that second-hand smoke exposure can also effect births, but little was known about the impact of smoking bans on preterm birth rates.
So a team of researchers led by Tim Nawrot of Belgium's Hasselt University investigated trends in preterm births - before 37 weeks gestation - from 2002 to 2011 covering a period before, during and after the introduction of smoke-free laws.
They found the risk of preterm birth after the introduction of each phase of Belgium's smoking ban, which was implemented in three phases - in public places and most workplaces in January 2006, in restaurants in January 2007, and in bars serving food in January 2010.
No decreasing trend in preterm was evident in the years or months before the bans, the researchers said in their study in the British Medical Journal on Friday.
"Our study shows a consistent pattern of reduction in the risk of preterm delivery with successive population interventions to restrict smoking," the researchers wrote.
"It supports the notion that smoking bans have public health benefits even from early life."
Smoking causes lung cancer, often fatal, and other chronic respiratory diseases. It is also a major risk factor for cardiovascular diseases, the world's number one killers.
According to the World Health Organisation, tobacco already kills around 6 million people a year worldwide, including more than 600,000 non-smokers who die from exposure to second-hand smoke. By 2030, if current trends continue, it predicts tobacco could kill 8 million people a year.
Public health experts hope that as more and more countries in Europe and around the world adopt stricter legislation on smoking in public places, the health benefits will start to become evident fairly swiftly.
A study from England published last month found that the introduction of smoking bans there led to swift and dramatic falls in the number of children admitted to hospital suffering asthma attacks.
And research published in 2009 also found the ban on smoking in public places in England led to a swift and significant drop in the number of heart attacks, saving the national health service 8.4 million pounds ($13.1 million) in the first year.
The Belgian researchers analysed 606,877 live, single-born babies delivered at between 24 and 44 weeks of gestation in Flanders from 2002 to 2011.
The results show a reduction in the risk of preterm births of 3.13 percent after January 2007, and a further reduction in the risk of 2.65 percent after January 2010.
($1 = 0.6433 British pounds) (Editing by Paul Casciato)