Study links radon to increased risk of stroke

NEW YORK, Jan. 31 (UPI) -- Exposure to even moderate levels of radon -- a invisible, odorless gas that is the second-leading cause of lung cancer -- has been linked to an increased risk of stroke, a new study reveals.

The study was published Wednesday in the online issue of Neurology, the medical journal of the American Academy of Neurology.

In investigating exposures in middle age to older female participants, researchers found an elevated risk of stroke among those exposed to high and even moderate concentrations of the indoor air pollutant compared to those exposed to the lowest concentrations.

However, the study doesn't prove that exposure to radon causes stroke -- it only shows an association.

"Radon is a naturally occurring radioactive gas produced when metals like uranium or radium break down in rocks and soil," according to a news release. "The gas can make its way into homes through cracks in basement walls and floors, construction joints and gaps around pipes."

The role of radon "in lung cancer is established. Yet, to date, we've known very little about its role in the epidemiology of relatively common cardiovascular diseases, like stroke," Dr. Eric A. Whitsel, the study's senior and corresponding author, told UPI via email.

"U.S. women shoulder a disproportionate burden of stroke at older ages," said Whitsel, a professor of epidemiology at the UNC Gillings School of Global Public Health at the University of North Carolina-Chapel Hill.

"So, we thought it would be helpful to study the association between radon and stroke among a very large population of middle-age and older women across the U.S. Our study found positive associations between common home radon concentrations and risk of stroke among them."

Whitsel, also an adjunct professor of medicine at the University of North Carolina's School of Medicine, added that the findings are potentially important because researchers observed associations at radon concentrations as many as 2 units fewer than the U.S. Environmental Protection Agency's lung cancer-based threshold for recommending a home radon mitigation system.

That threshold- - the EPA's "Radon Action Level" -- is set at 4 picocuries per liter of air, he said.

The study included 158,910 female participants, averaging 63 years old, who had not had a stroke at the start. Researchers followed them for an average of 13 years. During the study, participants experienced a total of 6,979 strokes.

By linking participants' home addresses to radon concentration data from the U.S. Geological Survey and the EPA, researchers were able to determine radon exposures.

Participants were divided into three groups. The highest group lived in in areas in which average radon concentrations exceeded 4 pCi/L. The middle group had homes in locations with average concentrations between 2 and 4 pCi/L. The lowest group was in areas with average concentrations of less than 2 pCi/L.

In the group with the highest radon exposures, researchers documented 349 strokes per 100,000 person-years compared to 343 strokes in the middle group and 333 strokes in group with the lowest exposure. Person-years represent the number of people in the study and the length of time each individual spends in the study.

After adjusting for factors such as smoking, diabetes and high blood pressure, researchers found participants in the highest group had a 14% increased risk of stroke compared to those in the lowest group. Those in the middle group had a 6% heightened risk.

More studies would be necessary to confirm the findings. Such confirmation would offer an opportunity to address an emerging risk factor for stroke and to ultimately improve public health, Whitsel said.

A limitation of the study was its inclusion of only female participants who were middle-age or older and predominantly white, so the results may not be the same for other populations, the study noted.

The work was funded by the National Institute of Environmental Health Sciences and National Heart, Lung, and Blood Institute.

The results open physicians' eyes to think beyond the common risk factors for stroke, such as smoking, hypertension, cholesterol, diabetes and obesity, Dr. Jason Mathew, a vascular neurologist at the Stony Brook Cerebrovascular and Comprehensive Stroke Center in Stony Brook, N.Y., told UPI in a telephone interview.

"This study forces us to look outside of those traditional risk factors," Mathew said. But the risk factors "all build on one another. If you're a smoker and if you live in an area that has high radon exposure, then it increases your risk even more."

As a result, controlling your own risk factors become even more important, especially as we continue to learn more about the impact of the environment on our stroke risk, he said.

Women are disproportionately affected by stroke and have poorer outcomes than men, Dr. Sarah Song, a neurologist and stroke specialist at Rush University System for Health in Chicago, told UPI via email.

"Given the potential for radon exposure in the home, and that historically, more women are in the home for longer periods of time, this study looked at the association between home radon exposure and the risk of stroke in middle-aged and older women," Song said, adding that radon also can exist in some workplaces.

However, the public shouldn't panic in response to the study, Dr. Rodica Di Lorenzo, a vascular neurologist at Cleveland Clinic, told UPI via email.

While the results showed significantly elevated risk of stroke with higher doses of radon exposure compared to lower doses, the relative risk increase was moderate after adjusting for possible confounding variables, Di Lorenzo said.

"The more we know about causes of stroke, the better we can prevent it. Not infrequently, stroke neurologists struggle to identify the reason why someone suffered a stroke," she said.

"In those cases, it is helpful to be aware of other factors, such as exposure to environmental ionizing radiation that can be measured and mitigated."

Efforts should be made to promote better residential radon testing behaviors and to implement mitigation measures involving ventilation practices and house construction, Dr. Deepak Gulati, medical director of the telestroke collaborative at Ohio State University's Wexner Medical Center's Comprehensive Stroke Center in Columbus, told UPI via email.

Further studies to confirm this positive association between radon exposure and increased stroke risk could lead to revision of national guidelines and policies, Gulati said.