Smoking habits in parents can remotely affect the health of their children who might suffer from respiratory problems later in their life, a study has said.

Children who do not show any signs of respiratory problems may still be experiencing damaging changes in their breathing process that could lead to lung disease later in life, according to a new study presented at the American Thoracic Society 2007 International Conference on Sunday.

"Everyone knows that children whose parents smoke have more respiratory problems - more puffing, wheezing, cases of pneumonia - but until now we haven't known if lung function is impaired in the children who don't have any respiratory complaints or diagnosed lung problems," researcher Bert Arets of University Medical Center Utrecht in the Netherlands said.

The study included 244 children ages 4 to 12 without any history of lung or respiratory disease.

They were divided into four groups according to the smoking pattern of their parents: persons who have never smoked, smoking after birth but not during pregnancy, during pregnancy but not after birth, and both before and after birth.

The researchers found that children of parents who smoke had significantly reduced lung function similar to that seen in smokers.

Smoking after birth appeared to be more harmful than smoking during pregnancy.

The researchers have now expanded their study to include 2,000 healthy children of the parents who smoke.