Radon, a naturally occurring radioactive gas produced when metals like uranium or radium break down in rocks and soil, is a known cause of lung cancer.
Now new research has found exposure to high levels of this indoor air pollutant is associated with an increased risk of another condition in middle-aged to older female participants with ischemic stroke.
Exposure to even moderate levels of radon — an 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.
“Our study found positive associations between common home radon concentrations and risk of stroke among them,” said Dr. Eric A. Whitsel, a professor of epidemiology at the UNC Gillings School of Global Public Health at the University of North Carolina-Chapel Hill.
In investigating exposures in middle-aged 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.”
Because data has consistently linked lung cancer and exposure to radon – a colorless, odorless gas that can build up in homes – the Environmental Protection Agency (EPA) identifies radon as the number one cause of lung cancer among non-smokers in the United States.
However, the two new studies, led by researchers in the Department of Epidemiology, found that moderate-to-high home radon concentrations also may increase risk of stroke, a much more common disease among middle-aged and older women.
Moreover, they found that the increased risk of stroke may depend on radon-related mutations that allow certain kinds of white blood cells to rapidly multiply, a condition called clonal hematopoiesis (CH).
“Radon is a radioactive gas released by the decay of elements like uranium and radium that are often found in rocks and soils,” said Sophie Buchheit, AB, who is a MedServe/Americorps Fellow and lead author of the first study.
“It also enters homes through basement floor slabs, porous or cracked foundation walls, and crawlspaces, making exposures common and unrecognized,” added doctoral student Jason Collins, MPH, co-author of both studies. “Furthermore, radon is a known cause of acquired genetic mutations.”
The transition to menopause increases the risk of stroke, and the risk nearly doubles in the ten years after menopause, but little is known about the role that common indoor air pollutants like radon play in that risk. The first study, published today in Neurology®, followed more than 150,000 postmenopausal women without a history of stroke for 13 years to determine whether common home radon concentrations were associated with increased stroke incidence.
The EPA recommends fixing homes with radon concentrations of four or more picocuries per liter (pCi/L) of air to reduce the risk of lung cancer, but it also recommends considering repairs when radon concentrations are between two and four pCi/L. The study participants were divided into the highest, middle and lowest home radon concentration groups based on where they lived: more than four pCi/L, between two and four pCi/L, and less than two pCi/L.
Researchers found that those in the highest radon group had a 14% increased risk of stroke relative to those in the lowest group. Those in the middle radon group had a 6% increased risk.
“It’s important to note that we found an increased number of incident strokes among women living in areas with radon concentrations as many as two pCi/L below the current lung cancer-based threshold for recommending radon mitigation,” said Eric Whitsel, MD, MPH, professor of epidemiology at the Gillings School and senior author on both studies. “More studies are needed to confirm our findings. Confirmation would present an opportunity to improve public health by addressing an emerging risk factor for stroke.”
The second study, published earlier this month in Neurology®, sought to understand whether high home radon concentrations are also associated with CH, a condition caused by acquired genetic mutations in white blood cell precursors.
“Previous research has shown that women with CH have a higher risk of cardiovascular diseases like stroke and blood cancers like leukemia,” noted doctoral student and lead author, Kurt Anthony, MPH.
In a study of more than 10,000 postmenopausal women, the team found stronger associations between home radon concentrations and CH among women with incident stroke. The associations were strongest among women with ischemic stroke and, in particular, cardioembolic stroke, but not other forms of stroke or among women without stroke. Cardioembolic strokes often occur when blood clots in the heart move through arteries to the brain where they damage it by blocking flow of oxygen- and nutrient-containing blood.
Although findings from neither study provide definitive proof that radon is the direct cause of CH or stroke, the research team says it’s important for future studies to further examine these associations to better inform public health recommendations that, to-date, only advise home radon mitigation at concentrations of four or more pCi/L with the goal of preventing lung cancer, a societally burdensome but far less common disease.
“While we are waiting on that research,” Whitsel said, “I suggest following current advice but emphasize that doing so also includes considering mitigation when home radon concentrations are two to four pCi/L, especially if someone living in the home smokes.”