The dangers of smoking on users and their children are known but new research demonstrates that it also can causes asthma in their grandchildren.

Asthma is a major public health problem. It is the most common chronic disease of childhood. While there are many factors which contribute to asthma - maternal smoking during pregnancy is a well known, and avoidable, risk.

During pregnancy nicotine can affect a developing foetus' lungs, predisposing the infant to childhood asthma.

Researchers from Harbor-UCLA Medical Centre, California, tested the effect of nicotine exposure during pregnancy on rats, looking not only at their pups but also at second generation pups.

Exposure inside the uterus resulted in both male and female offspring having reduced lung function consistent with asthma.

It also impaired lung function of their own offspring, even though the first generation rats were not themselves exposed to nicotine once they were born, according to an UCLA statement.

Levels of proteins increased by maternal smoking in the lungs of their offspring such as fibronectin, collagen and nicotinic aceylcholine receptors, were also found to be raised in the grandchildren.