Long-Term Exposure to Air Pollution and Rate of Cognitive Decline

In a study published in Neurology researchers found an association of air pollution levels with cognitive impairment and decline in 1 of 2 large groups but not both. Both groups were ethnically and racially diverse and lived in the Northern Manhattan area of New York City. Participant's residential addresses were used to determine their exposure to pollution, which, on average, were similar for both groups. 

In the Washington Heights-Inwood group, people with more exposure to higher levels of air pollution had lower cognitive test scores at the beginning of the study and more rapid rates of decline in those scores. Exposure to nitrogen dioxide was linked to an accelerated rate of cognitive decline compared with the age of 1 year. Results were similar for fine and respirable particulate matter.

In the Northern Manhattan group, however, researchers did not find an association between cognitive function and air pollution. Study author Erin R Kulick, PhD, MPH, of Brown University School of Public Health in Providence, RI, and a member of the American Academy of Neurolog. Kulick suggests the difference in results may be because the second group was much smaller and only had 1 round of follow-up compared with 6 rounds for the first group.

“As people live longer lives and the aging population grows, age-related cognitive decline is a growing public health concern with profound social, economic and health effects, so finding ways to reduce the risk is important,” said y. “Air pollution can affect large populations of people because it has known cardiovascular risks, and previous research has found that it may also contribute to cognitive decline. However, the results of our research were mixed.” 
There were 5,330 participants with an average age of 75 enrolled in the Washington Heights-Inwood Community Aging Project, and 1,093 people with an average age of 70 enrolled in the Northern Manhattan Study. The group from the Washington-Heights-Inwood study of 5,330 participants was followed an average of 7 years with 6 rounds of follow-up testing every 18 months to 2 years. The Northern Manhattan study group of 1,093 participants was followed for 5 years with 1 follow-up round of testing.

All participants were given medical exams at the beginning of the study as well as cognitive tests to measure memory, language skills and executive function. 
The pollutants measured were nitrogen dioxide and 2 groups of particulate matter, particles of liquids or solids suspended in air that were less than 2.5 microns in diameter called fine particulate matter and particles that were less than 10 microns in diameter called respirable particulate matter. Average levels of air pollutants were similar for both groups of participants. In each group, participants were divided into 4 groups based on their air pollution exposure.

Researchers found that participants in the Washington-Heights Inwood study were exposed to a yearly average of 32 parts per billion of nitrogen dioxide, 13 micrograms per cubic meter (μg/m3) of fine particulate matter and 21 μg/m3 of respirable particulate matter The US Environmental Protection Agency (EPA) considers up to 53 parts per billion to be a safe level of yearly average exposure to nitrogen dioxide, up to 12 μg/m3 for fine particulate matter and up to 50 μg/m3 for respirable particulate matter.

“While the levels were in the range considered safe by the EPA, it’s possible that these results reflect higher levels from an earlier point in time. It also raises the question of whether the federal levels are low enough to protect people’s health,” said Kulick.