Cognitive connections
Most research on air pollution has focused on a type of
pollutant known as fine particulate matter. These tiny
particles — 1/30th the width of a human hair — are spewed
by power plants, factories, cars and trucks. Due to its known
cardiovascular effects, particulate matter is one of six principal
pollutants for which the Environmental Protection Agency
(EPA) has established air quality standards.
It now seems likely that the harmful effects of particulate
matter go beyond vascular damage. Jennifer Weuve, MPH, ScD,
an assistant professor of internal medicine at Rush Medical
College, found that older women who had been exposed to
high levels of the pollutant experienced greater cognitive
decline compared with other women their age (Archives of
Internal Medicine, 2012). Weuve’s team gathered data from
the Nurses’ Health Study Cognitive Cohort, a population that
included more than 19,000 women across the United States,
age 70 to 81. Using the women’s address history, Weuve and
her colleagues estimated their exposure to particulate matter
over the previous seven to 14 years. The researchers found that
long-term exposure to high levels of the pollution significantly
worsened the women’s cognitive decline, as measured by tests
of cognitive skill.
Weuve and her colleagues investigated exposure to both
fine particulate matter (the smallest particles, less than 2. 5
micrometers in diameter) and coarse particulate matter (larger
particles ranging from 2. 5 to 10 micrometers in size).
“The conventional wisdom is that coarse particles aren’t as
important as fine particles” when it comes to human health,
Weuve says. Previous studies in animals and human cadavers
had shown that the smaller particles can more easily penetrate
the body’s defenses. “They can cross from the lung to the blood
and, in some cases, travel up the axon of the olfactory nerve
into the brain,” she says. But Weuve’s study held a surprise. She
found that exposure to both fine and coarse particulate was
associated with cognitive decline.
Weuve’s results square with those of a similar study by
Melinda Power, a doctoral candidate in epidemiology and
environmental health at the Harvard School of Public Health.
Power and her colleagues studied the link between black
carbon — a type of particulate matter associated with diesel
exhaust, a source of fine particles — and cognition in 680
older men in Boston (Environmental Health Perspectives, 2011).
“Black carbon is essentially soot,” Power says.
Power’s team used black carbon exposure as a proxy for
measuring overall traffic-related pollution. They estimated
each man’s black carbon exposure by cross-referencing their
addresses with an established model that provides daily
estimates of black carbon concentrations throughout the
Boston area. Much like Weuve’s results in older women, Power
and colleagues found that men exposed to high levels of black
carbon had reduced cognitive performance, equivalent to aging
by about two years, as compared with men who’d had less
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black carbon exposure.
But while black carbon is a convenient marker of air
pollution, it’s too soon to say that it’s what’s causing the
cognitive changes, Power says. “The problem is there are a lot
of other things associated with traffic — noise, gases — so we
can’t say from this study that it’s the particulate part of the air
pollution that matters.”
Still, the cumulative results of these studies suggest that air
pollution deserves closer scrutiny as a risk factor for cognitive
impairment and perhaps dementia.
“Many dementias are often preceded by a long period of
cognitive decline. But we don’t know very much about how to
prevent or delay dementia,” Weuve says. If it turns out that air
pollution does contribute to cognitive decline and the onset
of dementia, the finding could offer a tantalizing new way to
think about preventing disease. “Air pollution is something that
we can intervene on as a society at large, through technology,
regulation and policy,” she says.
Young minds
Research is also finding air-pollution-related harms to
children’s cognition. Shakira Franco Suglia, ScD, an assistant
professor at Boston University’s School of Public Health, and
colleagues followed more than 200 Boston children from
birth to an average age of 10. They found that kids exposed
to greater levels of black carbon scored worse on tests of
memory and verbal and nonverbal IQ (American Journal of
Epidemiology, 2008).
More recently, Frederica Perera, DrPH, at the Columbia
University Mailman School of Public Health, and colleagues
followed children in New York City from before birth to age
6 or 7. They discovered that children who had been exposed
to higher levels of urban air pollutants known as polycyclic
aromatic hydrocarbons while in utero were more likely to
experience attention problems and symptoms of anxiety and
depression (Environmental Health Perspectives, 2012). These
widespread chemicals are a byproduct of burning fossil fuels.
Meanwhile Mohai, at the University of Michigan, found
that Michigan public schools located in areas with the highest
industrial pollution levels had the lowest attendance rates and
the greatest percentage of students who failed to meet state
testing standards, even after controlling for socioeconomic
differences and other confounding factors (Health Affairs,
2011). What’s worse, the researchers analyzed the distribution
of the state’s public schools and found that nearly two-thirds
were located in the more-polluted areas of their districts. Only
about half of states have environmental quality policies for
schools, Mohai says, “and those that do may not go far enough.
More attention needs to be given to this issue.”
Although Michigan and Massachusetts may experience areas
of poor air quality, their pollution problems pale in comparison
to those of Mexico City, for example. In a series of studies, Lilian
Calderón-Garcidueñas, MD, PhD, a neuropathologist at the
MONITOR ON PSYCHOLOGY • JULY/AUGUST 2012
