Radon is the second leading cause of lung cancer. Now a new study has found that exposure to this invisible, odorless gas is also linked to an increased risk of stroke. The study, which looked at midlife exposures in older women, found an increased risk of stroke in those exposed to high to moderate concentrations of the gas compared with those exposed to the lowest concentrations. The study is published in the January 31, 2024 online issue Neurology®, the medical journal of the American Academy of Neurology. The study does not prove that radon exposure causes stroke. shows only a correlation.
Radon is a naturally occurring radioactive gas produced when metals such as uranium or radium decay in rocks and soil. Gas can enter homes through cracks in basement walls and floors, construction joints, and gaps around pipes.
“Radon is an indoor air pollutant that can only be detected through tests that measure concentrations of the gas in homes,” said study author Eric A. Whitsel, MD, MPH, of the University of North Carolina at Chapel Hill. “Our research found an increased risk of stroke among participants exposed to radon above — and up to two picocuries per liter (pCi/L) below — concentrations that typically trigger EPA recommendations to install a home system radon mitigation’.
The study included 158,910 female participants with an average age of 63 who did not have a stroke at the start of the study. An average of 13 years was followed. During the study, there were 6,979 strokes among the participants.
To determine radon exposure, the researchers linked participants’ home addresses with radon concentration data from the US Geological Survey and the US Environmental Protection Agency (EPA).
The EPA recommends that average indoor radon concentrations not exceed four picocuries per liter (pCi/L). For concentrations this high, the EPA recommends installing a radon mitigation system to reduce radon levels in the home.
The participants were divided into three groups. The highest group had homes in areas where average radon concentrations were more than four pCi/L. The middle group lived in areas with average concentrations between two and four pCi/L. The lowest group lived in areas with average concentrations of less than two pCi/L.
In the group with the highest radon exposures, there were 349 strokes per 100,000 person-years compared with 343 strokes in the middle group and 333 strokes in the group with the lowest exposure. Person-years represent both the number of people in the study and the time each person spends in the study.
After adjusting for factors such as smoking, diabetes and high blood pressure, the researchers found that 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% increased risk.
“It is important to note that we found an increased risk of stroke among those exposed to radon concentrations up to two pCi/L below the current lung cancer-based threshold for the radon mitigation recommendation,” Whitsel said. “More studies are needed to confirm our findings. Confirmation would provide an opportunity to improve public health by addressing an emerging risk factor for stroke.”
A limitation of the study was that it only included female participants who were middle-aged or older and mostly white, so the results may not be the same for other populations.
The study was funded by the National Institute of Environmental Health Sciences and the National Heart, Lung, and Blood Institute.