Bad air for growing brains and minds

Mexico City’s air pollution may be undermining neural and mental functioning in some children

Mexico City wears a thick coat of air pollution that clogs lungs and takes a toll on hearts and blood vessels. But that’s just the beginning — the metropolis’s dirty air may have contributed to brain inflammation and intellectual deficits in at least some school-age children, a new study suggests.

Among healthy children aged 7 to 18, lifelong Mexico City residents scored lower than their peers from Polotitlán — a Mexican city with low levels of air pollution — on tests of memory, flexible thinking, novel problem-solving skill and the ability to monitor and change one’s behavior during challenging tasks, scientists report in an upcoming Brain and Cognition. These tests make up part of standard IQ measures for school children.

What’s more, brain scans of many Mexico City youngsters revealed alterations that can impair the prefrontal cortex, a neural region heavily involved in memory and thinking skills, say environmental pathologist Lilian Calderón-Garcidue±as of the University of Montana in Missoula and her colleagues.

Similar brain alterations, as well as evidence of neural inflammation, appeared in 1- to 2-year-old dogs that had grown up in Mexico City, the investigation finds.

Widespread declines in intelligence of the type and magnitude observed in the new report would have a huge impact on a country’s economic productivity, says psychologist and study coauthor Randall Engle of the Georgia Institute of Technology in Atlanta. “Saving money by failing to curb pollution truly is a matter of ‘pay me now or pay me later,’” Engle says.

Although their findings are preliminary, the researchers hope to conduct a five-year study tracking large groups of children living in areas with low and high air pollution. The most common air pollutants in Mexico City are particulate matter, which contains a complex mixture of various substances, and ozone. Polotitlán’s air contains low concentrations of all major pollutants.

“The growing brain may be vulnerable to the inflammatory effects of air pollution’s fine particulate matter as well as to specific chemicals that are toxic to brain growth,” comments neuropsychologist Sidney Segalowitz of BrockUniversity in St. Catharines, Canada.

Children in Mexico City and Polotitlán showed large neural and cognitive differences that need to be confirmed in further work, remarks epidemiologist David Bellinger of Children’s Hospital Boston. The new study didn’t measure the composition of Mexico City air pollution, so chemical culprits possibly responsible for the results remain unknown, Bellinger notes. Children’s increased lead exposure in Mexico City could also have contributed to lower scores on mental tasks, he adds.

Blood testing before admission to the study found no differences in average lead concentrations of Mexico City and Polotitlán children, Calderón-Garcidue±as says.

She and her coworkers recruited 55 children from Mexico City and 18 children from Polotitlán. All children came from middle class families and had no serious health problems.

Mexico City kids generally scored lower on specific memory and reasoning tests than their counterparts did. Using magnetic resonance imaging, or MRI, on a subset of the children, the researchers observed tissue alterations typical of inflammation in the brains of 13 of 23 Mexico City youngsters and 1 of 13 Polotitlán children.

Neural alterations were located near the front of the brain in tissue that could obstruct nerve transmissions sent to and from the prefrontal cortex.

In three Mexico City children who received another round of MRI scans 11 months after initial testing, frontal-brain tissue alterations remained the same.

Calderón-Garcidue±as’ team then conducted brain studies of seven healthy Mexico City dogs and 14 healthy dogs from Tlaxcala, another Mexican city with low levels of air pollution. All dogs were mixed breeds and had been reared at animal research facilities.

Comparable inflammation-related tissue alterations in the frontal brain appeared in four of seven Mexico City dogs and none of the others. In tissue analyses, brains of Mexico City dogs also displayed particularly high levels of substances produced by two genes that have inflammatory effects on the brain.

In studies conducted since 2002, the researchers have reported signs of brain inflammation and brain disease in dogs exposed to Mexico City’s air. Earlier this year, the researchers found that chronic exposure to air pollution was associated with markers of brain inflammation and increased brain immune responses in children and young adults who had died suddenly and were studied at autopsy. These individuals also possessed high levels of brain proteins thought to contribute to Alzheimer’s and Parkinson’s diseases.

Bruce Bower has written about the behavioral sciences for Science News since 1984. He writes about psychology, anthropology, archaeology and mental health issues.

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