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Long-term exposure to air pollution and road traffic noise may raise the risk of developing heart failure, especially among former smokers and people with high blood pressure, according to a large study of Danish women.

As the level of exposure to road noise and two common air pollutants – fine particulate matter and nitrogen dioxide – rose, so did the women's risk for heart failure, when the heart muscle is unable to pump blood properly. The research published Wednesday in the .

Air pollution had a larger impact than road noise on the risk for heart failure, but women exposed to high levels of both were most likely to develop the condition.

"We were surprised by how two environmental factors – air pollution and road traffic noise – interacted," lead author Youn-Hee Lim said in a news release. Lim is an assistant professor in the section of environmental health within the department of public health at the University of Copenhagen in Denmark. "To minimize the impact of these exposures, broad public tactics such as emissions control measures should be implemented. Strategies like smoking cessation and blood pressure control must be encouraged to help reduce individual risk."

Lim and her team analyzed data for 22,000 women ages 44 and older who were followed for up to 20 years as part of the Danish Nurse Cohort study.

They found that for every 5.1 micrograms per cubic meter of air (µg/m3) increase in exposure to fine particulate matter over a three-year period, the risk for developing heart failure rose 17%. For every 8.6 µg/m3 increase in nitrogen dioxide exposure, the risk of heart failure increased by 10%. It rose 12% for every 9.3 decibel increase in road traffic noise exposure. But the biggest impact was among former smokers. When exposed to fine particulate matter, their risk for heart failure rose 72%.

High blood pressure played a role. About 12% of all participants had hypertension when they enrolled in the study. Among those eventually diagnosed with heart failure, 30% had a history of hypertension and, Lim said, "they were the most susceptible population to air pollution exposure."

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