Men, and especially teenaged boys, who smoke prior to conceiving children are more likely to have babies with asthma, according to the first study to discover this link, announced Monday in Germany.

The research looked at the smoking habits of 13,000 men and women who responded to survey questions, including whether they have smoked, when and for how long. They also indicated whether they stopped smoking before conceiving, according to a news release. Fathers who smoked prior to conception raised the chances of their unborn children having asthma, a condition that causes the airways to swell, leading to labored breathing and tightness around the lungs. At least 25 million Americans have asthma, and 7 million of them are children, according to the National Heart, Lung and Blood Institute.

It isn't exactly clear how smoking before conception could cause asthma, but air pollution is certainly a factor, the authors said. "This study is important as it is the first study looking at how a father's smoking habit pre-conception can affect the respiratory health of his children," said one of the study authors, Dr. Cecile Svanes, of the University of Bergen, Norway, in a statement. "Given these results, we can presume that exposure to any type of air pollution, from occupational exposures to chemical exposures, could also have an effect."

Mothers smoking prior to conception was not associated with increased asthma risk among the women in the survey. According to the announcement, fathers who had been smoking longer and fathers who began smoking before 15 were more likely to have babies born with asthma. "It is important for policymakers to focus on interventions targeting young men and warning them of the dangers of smoking and other exposures to their unborn children in the future," Svanes said. The findings were presented at the European Respiratory Society International Congress in Munich.

Source: C. Svanes, et al. Parental smoking prior to conception and asthma in offspring. European Respiratory Society International Congress. 2014.