Researchers who study cognitive decline are working to identify modifiable risk factors and other ways of reducing or delaying dementia. Epidemiological research has suggested that a high rate of exposure to airborne particulate matter (PM), or air pollution, is associated with decreased cognitive function. It has been unclear whether this is directly due to pollution or to other confounding factors. A recent longitudinal study published in the Archives of Internal Medicine found that older women subjected to high levels of PM experienced faster cognitive decline.
The sample of participants consisted of 14,204 women, age 70 and better, who were participants in the ongoing Nurses’ Health Study (NHS). In the NHS, participants complete questionnaires on a range of health topics every two years. Participants in this sample were administered a variety of cognitive tests every two years, over a period of six years. The researchers estimated the participants’ exposure to PM using a geographic information system (GIS) model of the approximate PM exposure at the participants’ addresses.
Using the GIS information and data collected by the US Environmental Protection Agency’s Air Quality System, the researchers were able to obtain estimates of both short-term and long-term exposure to fine and coarse PM. Because it is not yet feasible to supply research participants with individual air monitors for long-term studies, these estimates of PM exposure were indirect, gathered by air pollution monitors near each participants’ home. However, the model was able to provide very precise differences in levels of exposure at each address due to its extensive GIS and meteorological data.
Based on previous findings on both human and animal exposure to pollution, the researchers hypothesized that exposure to both fine PM (such as vehicle exhaust) and coarse PM (such as dust) would contribute to accelerated cognitive decline. In their analysis, the researchers controlled for potential confounding factors such as age, education, vascular health, and physical activity.
Participants who were exposed to the highest degree of long-term PM experienced significantly faster cognitive decline than those exposed to lower degrees of exposure, even when controlling for the confounding variables. It is unclear how PM had this effect, but, based on prior findings, it appears possible that fine PM might directly access the brain when breathed in, and that both fine and coarse PM increase the risk of cardiovascular disease, which is known to contribute to cognitive decline. The differences in cognitive decline between the highest- and lowest-exposure groups were equivalent to two additional years of cognitive aging. If these findings are replicated by future studies, it appears that reducing air pollution might be an effective way to reduce cognitive decline in our population.
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