Zhang X, Chen X, Zhang X. The impact of exposure to air pollution on cognitive performance. Proc Natl Acad Sci U S A. 2018;115(37):9193-9197.
To determine how cognitive performance is affected by cumulative and transitory exposures to air pollution as individuals age.
Observational study; air quality data was matched with cognitive tests using matched time and geographic locations.
China Family Panel Studies (CFPS) is a nationally representative longitudinal survey of Chinese communities, families, and individuals conducted in 2010 (baseline) and 2014 by the Institute of Social Science Survey (ISSS) of Peking University, China. There were 25,486 individual respondents (>9 years old) in 2010 and 2014 for a total of 50,972 comparative data points. After removing individuals with incomplete data (n=282) and all data without usable Air Pollution Index (API), weather information, or household demographics, there were a total of 31,955 dataset points (ie, observation points) analyzed.
Study Parameters Assessed
The CFPS survey in 2010 and 2014 contained 24 standardized mathematical questions and 34 word-recognition questions, each in ascending order of difficulty. A test score was determined when the participant incorrectly answered 3 questions in a row, with the last correct answer entered as the test score.
Daily measurements of air quality were based on the Air Pollution Index (API), which includes sulphur dioxide (SO2), nitrogen dioxide (NO2), and particulate matter less than 10 microns in diameter (PM10). The API is published by the Chinese Ministry of Environmental Protection. The study used the nearest city-level API measurements to gauge air quality of counties where CFPS surveys were taken over 1-day, 7-day, 30-day, 90-day, 1-year, 2-year, and 3-year exposures.
Primary Outcome Measures
Change in cognitive performance over time, as measured by mathematical and verbal tests; API measurements in respondents’ geographic areas at specific times were matched with test score patterns to determine effects of pollution. To evaluate how air pollution affects cognitive performance in older people, the research examined the cumulative effects on both types of tests in various age cohorts: 25-34, 35-44, 45-54, 55-64, and over 65 years of age.
There were 3 significant general findings from this study:
- Air pollution corresponded to worsening test scores. This was statistically significant for all data points except math test scores for 1-day and 7-day air pollution exposure.
- The longer the exposure window to air pollution, the more sizable the decline in cognitive performance.
- Air pollution appears have a greater negative impact on verbal than math test performance.
Also, there were statistically significant gender differences reflecting increased male vulnerability to air pollution. The pattern of verbal scores highlighted the decline in performance in the older cohorts and simultaneously indicated more pronounced decline in verbal skill in men with a widening of the gender gap in older people.
In summary, in this study the aging brain was affected negatively by air pollution—especially in older or less-educated men—as demonstrated by cognitive performance on math and verbal tests.
The aging of the world population during a time of worsening air quality1 has serious implications for health impacts on social welfare. Cognitive challenges impair functionality to varying degrees and become more pronounced with age; physical aging and cognitive decline often occur simultaneously. The study reviewed here did not exclude other conditions that might have contributed to the observed cognitive decline, such as pulmonary and cardiovascular disease, diabetes, neurological or psychiatric disorders, and dementia.2
The authors suggest that one possible mechanism for the disparity in gender performance is the stronger effect of air pollution on white matter (required more by verbal tests), because there are gender differences in white and gray matter.3
The pattern of verbal scores highlighted the decline in performance in the older cohorts and simultaneously indicated more pronounced decline in verbal skill in men with a widening of the gender gap in older people.
Since men in general are less likely to seek medical advice preventatively4 and are more susceptible to cognitive impairment from air pollution exposure than women, it is important to highlight the risks early and often during any medical encounters with them.
When we counsel patients about how to reduce damage from air pollution the focus should be primarily on minimizing exposure and overall risk:5
- Monitor your air. Consult local or national sources on daily air pollution levels to help you determine if elevations suggest that you limit outdoor activities or hot spots of pollution.
- Schedule your outdoor activities. Be mindful of peak levels of rush-hour traffic in the morning and early evening, and try to avoid those times when air pollution levels tend to be highest.
- Know your surroundings. Evidence from other studies indicates more health vulnerabilities in people living near busy highways and intersections.
- Avoid driving in peak traffic areas and at peak times. Exhaust levels can cause decreased air quality inside of cars.
- Determine your risk. Assess overall susceptibility risk based on existing conditions to enable you to balance risks of ongoing and future exposures.
- Use personal protection. Some people should be advised to use a face mask with effective filtering for the most harmful fine particulate matter (PM2.5).