Public smoking bans improve the health of children, say researchers who found fewer preterm births and hospital visits for childhood asthma attacks after those bans were enacted in North America and Europe.

Second-hand smoke is linked to stillbirth, preterm birth, birth defects, asthma and respiratory infections. Researchers recognized that laws against smoking in public places such as restaurants and work places could help but there hasn’t been an in-depth check of how well the bans protect children.

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Only a small minority of the world's population is covered by broad smoke-free laws.

In Friday’s online issue of the medical journal The Lancet, researchers examined the effect of smoke-free legislation on child health by combing through five studies in North America and six European studies that described national bans.

The studies included more than 2.5 million births and more than 247,000 asthma-related visits to hospital.

"Pooled estimates suggest that rates of both preterm birth and pediatric hospital admissions for asthma were reduced by 10 per cent," after smoke-free legislation was introduced, Aziz Sheikh, the study’s senior author and a physician-researcher at Brigham and Women's Hospital in Boston and his Dutch and Belgian co-authors concluded.

The researchers called smoking bans a cost-effective way to protect the health of children.

While 40 per cent of children worldwide regularly breathe second-hand smoke, the study’s authors said only a small minority of the world’s population is covered by broad smoke-free laws.

They added that while the findings point to the health potential of expanding smoke-free laws, the promise might need to be "tempered," given enforcement challenges and smoking patterns at home. 

The Public Health Agency of Canada's website says children regularly exposed to second-hand smoke are more likely to suffer damage to their lungs and to develop breathing problems such as asthma.

The research was funded by the Thrasher Research Fund, Lung Foundation Netherlands Long Term Fellowship, Maastricht University Medical Centre, and International Pediatric Research Foundation.