A new research paper links a specific kind of pollution to faster rates of cognitive decline.
Several years ago a massive survey of women called the Nurses' Health Study began collecting data on memory, thinking skills and other cognitive measures.
Jennifer Weuve of the Rush Institute of Healthy Aging in Chicago combined that data with information about air quality where the women lived.
In particular, she compared the level of particulate matter in the air with the change in cognitive scores over several years.
"The most important finding of our study is that women who were exposed to higher levels of ambient particulate matter over the long term experienced more decline in their cognitive scores over the four-year period that we followed them up."
If cognitive decline was more rapid where air quality was worse, how could the pollution be causing the loss of mental skills and function?
Weuve says the tiny particulates in the air might be getting into the brain directly. They're so small - 10 microns, one-thousandth of a millimeter - that they can evade the body's usual defenses and may be able to reach the brain either via the lungs or through the sinus passages in the head.
"Several studies have found that these particles - at least some of them - can actually get into the brain where they can cause inflammation and might even trigger some of those microscopic changes that are typical of Alzheimer's Disease."
Or it may be a more indirect effect. Numerous studies have identified an association between air pollution and cardiovascular disease, and the cognitive decline may be a result of damage to the blood supply.
For example, research published in the same journal as Weuve's paper, the Archives of Internal Medicine, found a higher risk of stroke on days when there were more particulates in the air. The fine particles were mainly from vehicle exhausts.
And a new study in the journal of the American Medical Association, JAMA, combined results of 34 studies and found a statistically significant association between heart attack risk and a wide range of air pollutants, excepting ozone.
The researchers say that as a risk factor for heart attack, air pollution isn't as dangerous as things like smoking and high blood pressure, but on the other hand, air pollution, especially for those in urban areas and industrialized countries, is an unavoidable part of daily life.