Living near a busy road can increase risk of asthma ...

Road traffic can increase the risk of asthma, reported the Daily Express. A study has shown that “genetically susceptible” children are nine times more likely to develop asthma if they live near a main road. Both_ The Sun_ and Daily Express state: “Traffic-related pollution near your home increases the risk of asthma and reduces lung growth in children.”

The story is based on a well-conducted study which considered the effects of various potential risk factors for asthma in children. It highlights the contributions of both genetic and environmental factors to risk of asthma in children.

Where did the story come from?

Muhammad Salam and colleagues of University of Southern California Keck School of Medicine, USA, conducted this research. It was funded by National Institute of Environmental Health Sciences, US Environmental Protection Agency, National Heart Lung and Blood Institute, California Air Resources Board and the Hastings Foundation. It was published in the peer-reviewed medical journal Thorax .

What kind of scientific study was this?

This was a cross-sectional study in which the researchers used data from the large Children’s Health Study population to look at two things. First, whether asthma was related to variations in two particular genes involved in the breakdown of chemicals such as those found in fuel emissions; and second, how risk is related to the level of exposure, e.g. living near a main road.

Data about asthma was collected from 3,124 children from schools in southern California, and samples from tooth brushings were used to extract genetic material to assess the gene variations.

Calculations were made of the distance that each child lived from a major road and and each road was coded according to how heavy the traffic was, for example, whether they were highways or connecting roads.

Children were then grouped according the age at which the diagnosis of asthma had been made. Using statistical methods the relationship between this and the presence of the genetic variation was looked at, adjusting for other factors that may have an effect such as smoking exposure, age and family history of asthma. If a link with the genetic variation was found, the researchers looked to see whether the strength of the link was changed by adjusting for distance from a major road, in addition to these other factors.

What were the results of the study?

The researchers found that 15.5% of the group had asthma. Children who had particular variations of genes studied were at an increased lifetime risk of having asthma. The odds of developing asthma were nine times higher in children with high risk variations in both genes and who also lived within 75 meters of a major road, compared with children who had none of these risk factors.

What interpretations did the researchers draw from these results?

The researchers concluded that these particular genetic variations increase the risk of asthma. In children who have these genetic variations, the risk of asthma is increased further if they live near a busy road.

What does the NHS Knowledge Service make of this study?

This is a well-conducted study showing that children with a particular genetic make-up are more susceptible to asthma. In addition, environmental factors such as living near a busy road increase this risk. There are several important points to be aware of when interpreting the findings of this study:

The participants in this study may not be representative of the population as a whole, as there may have been differences in social and demographic status between those who contributed tooth-brushing samples for genetic analysis and those who did not.
Diagnosis of asthma in this study was based upon parental reporting of a doctor’s diagnosis; therefore there may have been some inaccuracies and differences between participants in the actual diagnosis.
The risks and causes of asthma are multiple including hereditary links, previous illness, exposure to smoking and environmental factors such as pollutants.
The study did not consider the effects of pollution on lung growth, as suggested by the newspapers.
Asthma is a complex disease, but this study demonstrates that there are relationships between genetic and environmental factors.

Sir Muir Gray adds...

The association of a set of genetic variants with a disease may eventually prove helpful in developing new treatments, but are of little use except when there is a direct link between one particular variant and a disease, this occurs in the diesase Huntington's chorea.

However, in general, children should be exposed to as little pollution as possible.