Does Air Pollution Have a Negative Effect on Cognitive Function


effect of air pollution

There are several other relationships between air quality and respiratory health that have also been theorized. For example, reduced lung function is suspected in people who are constantly exposed to industrial or commercial emissions. But, the evidence for this is still very limited. Meanwhile, people that work outdoors may be at risk if they are exposed to poor air quality (i.e., ozone or PM10) over long periods of time.

Air Pollution Effects

A plane flying in the air with smoke coming out of it

The relationship between the effect of air pollution and cognitive impairment is more established. One study suggested that long term exposure to poor air quality (defined as over a month) could lead to a reduction in verbal fluency, reading fluency, and comprehension. Another study found that older adults were more likely to have poor spatial skills (based on mental visual activity tests). A third study found that people age 65 or older were at higher risk of having a psychiatric illness (SRA) if they were frequently exposed to poor quality indoor air. This was attributed to the fact that older adults already have more problems with memory and thinking than younger people.

The effect of air pollution and cognitive impairment was supported by several studies using multiple methods. In a study of kindergarten children, those that were most exposed to industrial or commercial emissions were found to have lower verbal IQ scores. However, the researchers determined that the IQ results did not reflect performance on IQ tests alone; rather, these differences may have resulted from differences in academic and social adjustment. Similarly, a study that compared the verbal and nonverbal IQ scores of elderly people ages 65 or older found significant differences between the two groups. However, the researchers determined that these differences did not account for the reduced verbal IQ scores, but they were unable to determine whether the lower IQ score was due to better performance on verbal tests or an actual decline in the verbal skills.

The scientists performed several other studies that provided evidence that there are individual fixed effects of air contamination on mental and physical health. For example, one study that looked at the effect of long-term pollution found that individuals age 65 or older who lived in areas with high levels of smog had poorer verbal IQ, poorer IQ test scores on academic tests, and were more likely to have abnormal brain functioning. Another study that focused on older individuals who lived in areas rich in diesel found that those individuals were also at a greater risk of being diagnosed with dementia and Alzheimer’s disease. In addition, these individuals were also more likely to smoke and to use tobacco products other than water. There were also significant differences in both sex and total level of tobacco use between these groups.

In another study that focused on the relationship between outdoor exposure to cigarette exhaust and cognitive performance, researchers controlled for the number of cigarettes smoked per day, the level of ambient air pollution, and the individual subject’s IQ. They found that those subjects exposed to higher levels of air pollution during their daily routines had lower IQs than those that did not. The positive results of this study can be explained by the “feedback” theory: the less polluted an area is, the lesser the potential for cognitive performance feedback to occur, and the more polluted an area is, the less the feedback will occur.

The scientists then conducted four experiments to test the theoretical predictions of the IQ finding. First, they tested the cognitive test scores of rural and urban residents separately, and found no significant difference in either group’s IQ scores. Second, they administered the IQ test as part of a survey of community residents and found a significant difference between the two groups. Finally, they controlled for the number of cigarettes smoked per day, and again, found that individuals living in polluted environments had lower IQs than those who did not.

These results are significant because the relationship between air pollution, IQ, and aging brain functions is causal, and not merely suggestive. It is now believed by researchers that the negative effect of air pollution on brain function is caused by the oxidative stress that occurs when exposed to poor quality air. Oxidative stress damages cellular proteins and DNA, and this can result in the formation of free radicals which cause a wide range of disease symptoms. While the mechanisms are not well understood, the current thinking is that the oxidative stress seen in polluted environments is the likely cause of the observed IQ decline.

End Note

A star filled sky

This study provides additional evidence that the relationship between air quality and cognitive performance is causal and not suggestive. Because it is observational and placebo-controlled, there is no reason to doubt the validity of the results. This evidence supports the conclusion that the use of air pollution controlling measures can benefit public health.

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