Decreased lung function is common among children of smokers, prevalent even among those who don't have asthma or exhibit other obvious signs of breathing problems, Reuters reported May 21.

"In contrast to earlier studies, the current study included only children totally free of respiratory disease (asthma) in the past and respiratory symptoms at the moment of measurement," said researcher Bert Arets of the University Medical Center Utrecht in the Netherlands. "Other studies included all children, irrespective of respiratory disease or symptoms. If you find abnormal lung function in the latter group, this appears logical. However, our study shows that disease-free and symptom-free does not mean normal lung function."

Arets added that lung function of apparently healthy children could worsen over time if exposure to tobacco smoke continues.

The findings were presented at a meeting of the American Thoracic Society.