Asthma: prenatal and postnatal exposure to polycyclic hydrocarbons in tobacco increase the risk

Prenatal exposure to polycyclic aromatic hydrocarbons (PAHs) and postnatal cigarette smoke promote the development of respiratory symptoms, or the occurrence of asthma in children between one and two years, suggests a study published in the journal "Chest".

PAHs are molecules produced by the combustion of organic matter, in particular from road vehicles as well as the kitchen or home heating, recall Dr. Rachel Miller at Columbia University in New York and colleagues.

The researchers assessed whether maternal exposure to these pollutants during pregnancy had an impact on respiratory function in children, and if the smoke could aggravate any respiratory problems.

They recruited 303 non-smoking pregnant women during pregnancy and in urban areas. During the third trimester of pregnancy, the levels of PAHs was measured in the home of every woman.

The researchers were able to follow 264 children a year and 169 over two years, questioning mothers about the exposure of children to tobacco.

The one-year results show that children whose mothers had been exposed to higher levels of PAHs during pregnancy do not have more respiratory symptoms than those whose mothers were not exposed.

However, these children have an increased cough and wheeze risk if they were exposed to more cigarette smoke shortly after birth (increased risk of 29%).

At the age of two years, combined with prenatal exposure to secondhand smoke increases the postnatal PAH times the risk of respiratory problems by 54% and probable asthma by 64%, while these two risk factors taken separately have no significant effect.

These results show that PAHs and passive smoking induce deleterious effects on respiratory function which can add up to encourage the development of asthma, said the researchers.

Measures taken to reduce the risk of respiratory diseases in children living in urban areas must take into account these multiple environmental exposures, they propose.