Turns out, traffic-related pollution is linked to the risk of asthma in children.
According to a research conducted by the Beth Israel Deaconess Medical Center, children living within a football field's length of major roadways had nearly three times the odds of pediatric asthma compared to children who lived four times farther away.
While physicians have long known that smog and pollution can bring on an asthma attack among children and adults suffering from asthma, researchers have remained uncertain about what role long-term exposure to certain pollutants might play in the development of the disease in children.
New research suggested that long-term exposure to traffic-related pollution significantly increases the risk of pediatric asthma, especially in early childhood.
"Our previous research demonstrated that living close to a major roadway and lifetime exposure to air pollutants were associated with lower lung function in seven- to ten-year-old children," said corresponding author Mary B. Rice. "We suspected that these exposures would also be associated with pediatric asthma."
To find out, Rice and colleagues analysed data from 1,522 Boston-area children born between 1999 and 2002 whose mothers had enrolled in a long-term study called Project Viva, which was established to examine how behavioral and environmental factors - such as sleep and eating habits or exposure to pollution - impact children's health.
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As part of Project Viva, mothers provided comprehensive medical, socio-economic and demographic information, including residential address histories.
Rice and colleagues used mapping technologies to determine the distance between each child's home address and the nearest major roadway.
The researchers also linked home addresses to census data and satellite-derived atmospheric data to calculate each participant's daily exposure to fine particulate matter (PM) - tiny particles suspended in the air that when inhaled deposit in the terminal sacs of the lung.
Fine PM originates from fuel combustion, including traffic, power plants, and other pollution sources.
The research team also examined children's daily exposure to soot, a component of fine PM also known as black carbon. Incompletely burned fossil fuels expelled from engines (especially diesel) and power plants produce black carbon, which is a known carcinogen and potent contributor to climate change.
Further analysis of the geographic data and Project Viva questionnaires revealed clear patterns. Most strikingly, living close to a major road was linked to childhood asthma at all ages examined.
"Children living less than 100 meters from a major road had nearly three times the odds of current asthma - children who either experience asthma symptoms or use asthma medications daily - by ages seven to 10, compared with children living more than 400 meters away from a major road," said Rice.
"Even in the Boston area, where pollution levels are relatively low and within Environmental Protection Agency standards, traffic-related pollutants appear to increase the risk of asthma in childhood", added Rice.
Lifetime exposure to black carbon and fine PM were also linked to asthma in early childhood (ages three to five years), but in mid-childhood (ages seven to 10 years), these pollutants were associated with asthma only among girls.
"Younger children spend a larger proportion of their time at home than school-aged children, and their airways are smaller and may be more likely to wheeze in response to pollution," said Rice. "This may explain why pollution exposure was most consistently linked to asthma in young children.
The study appears in the Journal of Allergy and Clinical Immunology.