Pollution can put minds in a fog
Older women at greater risk from particulate-laden urban air
Exhaust billows out of a car tailpipe (David Paul Morris, Getty Images / January 2, 2008)
Researchers recently found that older women are especially vulnerable to air pollution in urban areas, experiencing higher rates of mental decline when exposed to fine and coarse particulate matter over time.
Their study, which was published earlier this year in the Archives of Internal Medicine, surveyed 19,409 women ages 70 to 81 nationwide from the Nurses' Health Study Cognitive Cohort. The researchers estimated their levels of exposure to air pollutants starting in 1988, with cognitive tests administered three times at two-year intervals between 1995 and 2001.
Fine particulate matter, which is less than 2.5 microns in diameter or about 1/30th the width of human hair, can be found in motor vehicle exhaust and fuel-burning fumes. Coarse particulate matter is 2.5-10 microns in diameter, and includes dust from construction, roads and industry.
"The reason we care about size is that in general the smaller the particle, the better its ability to infiltrate the body's defenses (such as the lungs and circulation)," said Jennifer Weuve, epidemiologist and assistant professor at the Rush Institute for Healthy Aging, Rush University Medical Center, who led the study. "There's interesting data from animal studies to suggest some particles go from the nasal passages attached to nerve endings and travel up into the brain, which is a little terrifying."
Repeated bouts of exposure to high levels of particulate matter might be causing small infarcts — tissue death — which could accumulate and affect cognitive function, speculated Weuve, adding more research was needed.
Weuve said the study showed exposure led to cognitive changes similar to a woman aging two years, which might not seem important in an individual but would be significant on a population-wide basis, especially with the rising number of baby boomers. Reduced exposure, possibly through legislation mandating more curbs on pollution, could mean less heartache for individuals, families and society, she said.
"They will experience a slower rate of cognitive decline and then fewer people will reach that threshold of dementia in their lives. Their families and society will bear less of a burden from dementia," said Weuve.
Dr. Victoria Persky, professor of epidemiology at the University of Illinois at Chicago School of Public Health, said the findings were worrisome because air pollution at the exposures studied is so common.
"These are exposures that are seen right now around the country at various levels," said Persky. "The implications are that this is one more potential health effect of air pollution and we should continue to work on decreasing our exposure."
Another article in the same journal issue studied the association between changes in fine particulate matter and the risk of ischemic stroke in patients admitted to a Boston hospital between 1999 and 2008. The authors found that ischemic stroke was 34 percent higher on days with moderate levels of exposure compared with days with good levels.
Dr. Diana Kerwin, assistant professor in the division of geriatrics at Northwestern University Feinberg School of Medicine, noted that in the first study, women exposed to higher levels of air pollution over time reported an increase in transient ischemic attacks, when blood flow to the brain briefly stops.
"That tells you the vascular event likely has a very strong correlation with why they saw this increased risk in cognitive decline," said Kerwin.
Kerwin said the implications were important for primary care physicians and other doctors who should look at controlling other vascular risk factors, in the hopes of minimizing the potentially negative effects that air pollution could add. Healthier diets and more exercise could help keep vascular problems at bay, said Kerwin.