It’s well known that air pollution contributes to numerous health problems, including heart disease, diabetes, asthma, and other respiratory disorders. But evidence is accumulating that exposure to polluted air over time can also have a harmful effect on the brain, especially as people age—potentially leading to earlier or worse cognitive decline and even dementia.
In a study published in PNAS in September 2018, Chinese researchers found that people who had been exposed to more air pollution performed worse on standard tests of verbal and math ability compared with people who had less exposure. The language and math tests were conducted on individuals age 10 and older as part of the China Family Panel Studies, a nationally representative survey of Chinese families and individuals launched in 2010. Scientists compared individuals’ test results with local air-quality data during the three years prior to their interview day (the day on which they were tested). The longer people were exposed to polluted air, the more pronounced the effect was, especially among older adults.
Interestingly, pollution seemed to have a worse effect on verbal performance than on math performance, possibly because it affects the area of the brain associated with language. Pollution also had a stronger effect on men than on women, especially among those with less than a middle-school education. The authors concluded that “the damage on the aging brain by air pollution likely imposes substantial health and economic costs,” in part because cognitive functioning is critical for elderly people both in carrying out daily activities and in making financial decisions.
A working paper published in August 2018 by the National Bureau of Economic Research looked directly at the economic costs of the air pollution-dementia link. Researchers from Arizona State University looked at 15 years of Medicare records for almost 7 million U.S. adults age 65 and older. Using EPA air-quality data from the same time period, they tracked the individuals’ cumulative exposure to fine particle air pollution (known as PM2.5) along with their overall health and whether they were diagnosed with dementia. The researchers found that higher levels of exposure to fine-particle pollutants over a decade—even well below the thresholds mandated by the government—significantly increased the chances of a dementia diagnosis. Given the economic costs associated with dementia (including the impaired financial decision-making that the Chinese researchers discussed), the authors concluded that tightening of air-pollution regulations could result in enormous cost savings. They estimated that the EPA’s regulation of PM2.5 during the 2000s already saved the country some $150 billion in the form of reduced dementia rates.
Major outdoor sources of fine particles include motor vehicle exhaust, wildfires, and other operations that involve the burning of fuels such as wood, heating oil, or coal. Indoor sources include tobacco smoke, cooking (such as frying, sautéing, and broiling), burning candles or oil lamps, and operating fireplaces and fuel-burning space heaters.