CDC review of seven studies involving over 8,000 children suggests a link between childhood leukemia and exposure to high levels of auto exhaust. Direct cause-effect needs more study, researchers say.
Young children who are exposed to high levels of vehicle exhaust — such as what they'd encounter living near busy roads in urban areas — appear to have a greater risk of childhood leukemia, according to a Centers for Disease Control and Prevention review of seven previous studies.
The CDC's systematic review, published in the April issue of the American Journal of Preventive Medicine, says that in the USA an estimated 30%-45% of people in large urban areas live near major roads, "suggesting increased exposure to traffic-related air pollution and risk of adverse health outcomes."
The article says the studies reviewed by the CDC suggest "that childhood leukemia is associated with residential traffic exposure during the postnatal period, but not during the prenatal period."
The review found that children diagnosed with leukemia were "50% more likely to live near busy roads than children without leukemia," said Vickie Boothe, a CDC health scientist and lead author of the Journal article. "While the study found a link, it does not prove that living near a busy road causes leukemia."
The incidence of childhood cancer in the nation has been increasing since 1975, the report says. The most common form of childhood cancer is leukemia, representing about one-third of all cancers among children 14 and younger. The cause is unknown for about 90% of childhood leukemia cases.
The seven previous studies reviewed by the CDC researchers involved just over 8,000 children, said Tegan Boehmer, a CDC epidemiologist and a co-author of the article.
Previous research has demonstrated a connection between residential traffic proximity and such health problems as asthma, cardiovascular disease and premature mortality.
This was the first comprehensive scientific review of studies assessing the association between residential traffic exposure and childhood cancer. The article notes that a 2010 special report by the Health Effects Institute on its review of five childhood cancer studies concluded there was "inadequate and insufficient" evidence to determine causality between exposure to traffic pollution and childhood cancers.
Boothe and Boehmer say further research is needed to establish a cause-and-effect relationship between traffic and childhood leukemia, and to determine specifics on volume of traffic and distance from it that create a risk.
The study suggests that "precautionary public health messages and interventions designed to reduce population exposure to traffic might be warranted."