City Smog Linked to Cognitive Deficits in Children

For all the benefits of growing up urban, there are some considerable health risks too. In an upcoming issue of the journal Brain and Cognition, an international team of researchers reports that exposure to urban air pollutants "may perturb the trajectory of cerebral development and result in cognitive deficits during childhood." Simply put, the kids in cities may not be all right.

The researchers, led by Lilian Calderón-Garcidueñas of the National Institute of Paediatrics, in Mexico City, and the University of Montana, studied a group of 30 children aged 7 or 8 who had lived in Mexican cities their whole lives. Some came from Mexico City, a place known for its extremely high levels of air pollutants, while others lived in Polotitlán, a city with a strong air quality rating.

The researchers tracked the children for two years, using an array of tools — including brain scans — to measure volume of white matter, neuroinflammation, and cognitive performance in the youths. They found that the brains of kids from cleaner Polotitlán looked healthier than those of Mexico City children, and performed better too. On tests of complex reasoning, knowledge integration, and verbal and working memory skills, the Mexico City kids scored lower than did the other children. The researchers conclude:

Children who appeared to be healthy and had no risk factors for neurological or cognitive deficits, but who are residents in a highly polluted atmosphere, exhibited selective impairment in IQ subscales tapping on attention, short term memory and learning abilities. ...

If cognitive abilities are reduced during the critical childhood developmental years as a result of air pollution, it will have enormous detrimental effects on society.

While scientists have a good sense of how city smog harms the lungs and the heart, its impact on brain functioning has been poorly understood until late. The recent work of Calderón-Garcidueñas and others in her field is starting to inform this knowledge gap. In a study from 2008, Calderón-Garcidueñas and colleagues found that 56 percent of otherwise healthy Mexico City kids had lesions of the prefrontal cortex, compared with less than 8 percent of youths from a low-polluted region. At a recent professional meeting, covered by science reporter Janet Raloff, Calderón-Garcidueñas noted a troubling similarity between the types of brain abnormalities she's finding and the hallmarks of Alzheimer's disease.