The more researchers look into air pollution, the more problems it seems to cause.

Exposure to pollution has been linked to a number of major health problems, including cardiovascular disease and lung disease. It’s also been linked to dementia before, and some studies have even found that it can even impair cognitive ability. When it comes to other conditions, pollution is a modifiable risk. When the pollution is eliminated, the risk also drops, but for dementia, this hadn’t yet been demonstrated.

So a team of researchers led by Diana Younan, of the University of Southern California, carried out a study on 2,232 older women who were free of dementia when they entered the study. They chose to focus on women because older women are disproportionately affected by Alzheimer’s disease, Younan told ZME Science. The researchers then followed the women for 20 years, giving them two different cognitive tests every year. They also analyzed local changes in air quality for all of the women and used statistical analysis to see if a reduction in air pollution was associated with slower cognitive decline.

It was. Women living in areas with greater improvements in air quality tended to have a much slower decline, as indicated by cognitive tests. Basically, the reduced rate of decline in areas with greater air improvement was equivalent to being 0.9-1.6 years younger, depending on the test.

The findings strengthen the link between pollution and cognitive decline. In order to give context on how much air pollution can affect cognitive ability, the researchers compared the magnitude of their results with other known predictors of cognitive decline, such as age.

“We found that reducing air pollution exposure can promote healthier brain aging in older women by slowing cognitive decline. These benefits were seen in older women of all ages, levels of education, geographic regions of residence, and cardiovascular histories,” Younan says.

“Based on our results, we saw that an interquartile range increment of reduced PM2.5 (1.79 ug/m3) and of reduced NO2 (3.92 ppb) was associated with slower decline in cognition,” Younan told ZME Science. “This potential benefit was equivalent to the slower decline rate observed in women who were 1-1.5 years younger at baseline.”  

The good news is that environmental policies can help reduce pollutants, and consequently, help reduce the burden on people’s cognitive abilities.

“The health benefits seen in our study were a result of decreasing levels of both PM2.5 and NO2 across the U.S., which were likely due to national policies and strategies aimed at regulating pollution from stationary (power plants; factories) and mobile (vehicles) sources.”

Cleaner air is already known to improve heart and respiratory health, but in addition to the health component, there’s also an economic component to the study. Dementia is estimated to cost the U.S. economy $159–$215 billion annually, and reducing pollution could be an efficient way of reducing this financial burden.

The researchers were surprised to see that the benefits of reducing pollution levels were seen across older women of all ages — which is all the more reason to take measures to reduce atmospheric pollution, they say.

“Studies have shown that seniors, people with lower levels of education, people living in certain areas across the US, and people with preexisting heart disease are affected more by air pollution,” Younan concludes. “What surprised us and was the most important finding was that these benefits were seen in older women of all ages, levels of education, geographic regions of residence, and cardiovascular histories. The Clean Air Act mandates that the Environmental Protection Agency sets air quality standards to provide a safe margin for sensitive populations and these results suggest that the benefits may be universal in older women. I think these findings show that it is worth the continuing efforts to enforce air quality standards and provide more clear air to all.”