Children have an increased risk of developing asthma if their fathers smoked before they were conceived, a new study has found.

According to the findings, asthma is three times more common in children whose fathers smoked during adolescence compared to the children of never-smokers.

It is already widely known that a mother's environment has a key role to play in the health of her children. However, this study shows that this may also be the case for fathers.

Norwegian researchers looked at over 24,000 children from five countries, including Norway, Sweden and Estonia, and found that those whose fathers smoked prior to conception were at least three mores likely to develop early-onset asthma compared to children whose fathers never smoked.

Furthermore, the earlier a father started smoking and the longer he smoked during his life, the higher the risk of non-allergic, early-onset asthma in his children.

"The greatest increased risk for their children having asthma was found for fathers having their smoking debut before age 15. Interestingly, time of quitting before conception was not independently associated with offspring asthma," explained Prof Cecilie Svanes of the University of Bergen.

The study found that children were more likely to develop asthma if their mothers smoked around the time of pregnancy, which is consistent with previous research. However no link was found among women who smoked prior to conception. This suggests that smoking in men may affect their sperm cells, the researchers said.

"Smoking is known to cause genetic and epigenetic damage to spermatozoa, which are transmissible to offspring and have the potential to induce developmental abnormalities," Prof Svanes noted.

She added that there is growing evidence from animal studies of the importance of ‘epigenetic programming - a mechanism whereby the father's environment before conception could impact on the health of future generations'.

Details of these findings are published in the International Journal of Epidemiology.