MONDAY, Feb. 13 (HealthDay News) -- A lifetime's exposure to air pollution may contribute to mental decline in older women, a new study says.

Researchers used data from U.S. Environmental Protection Agency (EPA) air monitors combined with address information on more than 19,000 women aged 70 to 81 taking part in the U.S. Nurses' Health Study to calculate their exposure to air pollution over the course of seven to 14 years.

In addition to information from the air monitors, which measure six major pollutants, researchers took into account factors that could influence exposure, such as wind patterns, altitude and proximity of each woman's residence to major roadways.

The women also took an over-the-phone test to measure various mental abilities such as memory and thinking skills. The tests were repeated two and four years later.

Both exposure to fine particulate matter air pollution -- less than 2.5 micrometers in diameter, or about 1/30th of the diameter of a human hair -- and coarse particulate matter -- between 2.5 and 10 micrometers in diameter -- were associated with mental declines in women.

"Women who were exposed to higher levels of particulate matter over the long term experienced more decline in their cognitive scores over the four-year follow-up period," said lead study author Jennifer Weuve, an assistant professor at the Rush Institute for Healthy Aging in Chicago. "This association was true for both types of air pollution, both the fine and the coarse."

Every 10-unit increase in air pollution women were exposed to aged them mentally by the equivalent of about two years, according to the study in the Feb. 13 issue of the Archives of Internal Medicine.

On a population scale, the impact is tremendous, Weuve said. If millions of people are slightly older mentally than they would be otherwise, that has a huge impact on older women's quality of life, on their families and on the societal costs of taking care of them, she explained.

"Unlike other factors that may be involved with dementia, air pollution is unique because we can intervene in it as a society at large, through policy, regulation and technology," Weuve said.

Particulate air pollution -- particles of solid or liquid matter suspended in the air -- is made up of acids such as nitrates and sulfates, organic chemicals, metals and soil or dust, according to the EPA.

A major source of fine particulate matter pollution in the United States is combustion from cars, diesel engines and industry.

Sources of larger particles include roads, construction, mining, burning and farming.

Generally, scientists believe that the smaller the particle, the more it infiltrates the body, Weuve said. Smaller particles travel deeper into the lungs, and can enter the bloodstream.

Research in animals has also found that some particles, when inhaled, go directly from the nasal passage to the brain, she added.

Previous studies have found that exposure to air pollution is associated with cardiovascular disease. Cardiovascular disease, which involves the heart and blood vessels, has been shown to accelerate mental decline, Weuve said.

So the association between air pollution exposure and women's mental decline might be explained by pollution's impact on cardiovascular health. It's also possible that the air pollution is reaching the brain itself, leading to inflammation and potentially triggering the microscopic changes that mark the onset of Alzheimer's disease, she said.

Dr. Rajiv Bhatia, director of environmental health for the San Francisco Department of Public Health, said the findings were consistent with prior research that has shown pollution can contribute to respiratory and cardiovascular disease.

"It's fairly conclusive that fine particulate matter has effects on the cardiovascular system, and effects on the brain are also possible," Bhatia said.

The challenge, he said, is reducing particulate matter in levels where it's high, and reducing the disparities among those exposed. Research shows ethnic and racial minorities are more likely to live near sources of air pollution. such as roadways, ports and freight distribution centers.

"We're making progress, but there are areas and places where these levels are high and still increasing," he said. "People living near very busy roadways are disproportionately affected and have not seen much benefit from the Clean Air Act."

The Clean Air Act directs the EPA to reduce air pollution.

Since it took effect, levels of fine particulate matter have fallen in most areas, but in some areas, air pollution remains too high.

Bhatia, in an accompanying journal commentary, called for more air monitors near busy roadways to compel state governments and regional planning agencies to take steps to reduce pollution near those sources.

"If you don't have monitors near roadways, they are not forced to take action," Bhatia said.

Another study in the same journal by researchers at Brown University found that more people were admitted to a Boston hospital for ischemic stroke on days when levels of fine particulate air pollution were high. Ischemic stroke occurs when a blood vessel leading to the brain becomes blocked.

Ischemic stroke risk was 34 percent higher on days with "moderate" pollution levels than days with "good" levels, according to the EPA's Air Quality Index, the researchers found.

More information

The U.S. Environmental Protection Agency has more on air pollution.

SOURCE: Jennifer Weuve, M.P.H., Sc.D, assistant professor, Rush Institute for Healthy Aging, Rush University Medical Center, Chicago; Rajiv Bhatia, M.D., M.P.H., director, environmental health, San Francisco Department of Public Health; Feb. 13, 2012, Archives of Internal Medicine

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