Ask the Doctors by Eve Glazier, M.D. and Elizabeth Ko, M.D

Proximity to Freeway Traffic Linked to Asthma in Kids

Dear Doctor: We live near a freeway with a lot of traffic. Do I need to be worried about my kids developing asthma?

Dear Reader: This is a valid question. Cars release a number of small particles into the air that can irritate the lungs. This particulate matter, in addition to nitric oxide and black carbon, has been associated with asthma. Children are more vulnerable to the effects of pollution because their lungs and immune system are still developing.

An analysis of many studies, published in the journal Allergy, found a significant association between traffic-related air pollution and asthma. The association was seen as early as the age of 1 and increased as the child became older. The rise in asthma as kids get older seems to be related both to structural changes that pollution creates in the lungs and also to the extent of time that older children spend outside compared to younger children.

One other important aspect of asthma is that it can be exacerbated by stress. Noise pollution and the danger of cars in close proximity may worsen asthma symptoms in children because they can create a more stressful environment. This is an important factor if your child already has asthma.

A recent study in Minnesota evaluated the number of asthma cases in the emergency room, in the hospital and in a clinical setting. The researchers then looked at the proximity of people to a major source of traffic. After taking poverty out of the equation, which is in itself a risk factor for asthma, the researchers found that, as traffic density increased, so did the number of asthma exacerbations, or worsening of asthma symptoms. In this study, for every 10 percent increase in traffic density, there was a 15 percent increase in asthma-related visits to the emergency room, hospital or outpatient clinic.

Clearly, if you have a child with asthma, moving him or her away from traffic would indeed reduce the chance of a severe asthma attack.

I understand your concern. It is also a societal concern. Despite the evidence linking pollution to asthma, the levels of pollutants that are associated with an increased risk of asthma are well below the guidelines from the World Health Organization.

This doesn't mean that if you live near a freeway, you have to move. The majority of children who live near a freeway do not get asthma. But if your child is already showing signs of asthma at a young age, then moving to an area with fewer pollutants is perhaps something you should consider, if it is at all possible.

It took many years for our society to accept the ills of secondhand smoke from cigarettes. When it did, smoking was then banned from many public places, even casinos. It is more difficult to ban housing near freeways or heavily trafficked areas, especially when that housing already exists.

(Robert Ashley, M.D., is an internist and assistant professor of medicine at the University of California, Los Angeles.)

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