Exposure to even moderate concentrations of radon is associated with a significant increase in stroke risk, new research suggests.
Even moderate concentrations of radon were associated with a 6% higher stroke risk.
Radon is the second leading cause of lung cancer, but little was known about how exposure to the gas might affect stroke risk in women.
“Our research found an increased risk of stroke among participants exposed to radon above — and as many as 2 picocuries per liter (pCi/L) below — concentrations that usually trigger Environmental Protection Agency recommendations to install a home radon mitigation system,” senior author Eric A. Whitsel, MD, MPH, professor of epidemiology and medicine, University of North Carolina, Chapel Hill, said in a news release.
The study was published online on January 31, 2024, in Neurology.
Women Particularly Affected
Radon is a naturally occurring odorless radioactive gas produced when uranium or radium break down in rocks and soil. Its presence is increasing as a result of climate change, and it is increasingly being found in people’s homes. When inhaled, this air pollutant releases ionizing radiation in the lungs and is seen as second only to smoking as an established cause of lung cancer.
The National Radon Action Plan of the US Environmental Protection Agency (EPA) lays out testing and mitigation guidelines based on the known role of radon in lung carcinogenesis. But radon testing and mitigation are less common than recommended, and the EPA’s action plan doesn’t cover diseases other than lung cancer.
Compared with men, women have a higher rate of stroke and, in the US, typically spend about 11% more hours per day indoors at home, which investigators note highlights a “potential role of the residential environment among other risk factors specific to women.”
Researchers examined longitudinal associations between home radon exposure and incident stroke in 158,910 women at baseline (mean age 63.2 years; 83% White) over a mean follow-up of 13.4 years. During this time, participants experienced a total of 6979 strokes.
Participants’ home addresses were linked to radon concentration data drawn from the US Geological Survey and the EPA, which recommends that average indoor radon concentrations not exceed 4 pCi/L.
The highest radon exposure group resided in areas where average radon concentrations were < 4 pCi/L; the middle exposure group lived in regions with average concentrations of 2-4 pCi/L; and the lowest exposure group lived in areas with average concentrations < 2 pCi/L.
The researchers adjusted for demographic, social, behavioral, and clinical characteristics.
Public Health Implications
The incidence rates of stroke per 100,000 women in the lowest, middle, and highest radon concentration areas were 333, 343, and 349, respectively.
Stroke risk was 6% higher among those in the middle exposure group (adjusted hazard ratio [aHR], 1.06; 95% CI, 0.99-1.13) and 14% higher in the highest exposure group (aHR, 1.14; 95% CI, 1.05-1.22) compared with the lowest exposure group.
Notably, stroke risk was significant even at concentrations ranging from 2 to 4 pCi/L (P = .0004) vs < 2 pCi/L, which is below the EPA›s Radon Action Level for mitigation.
The findings remained robust in sensitivity analyses, although the associations were slightly stronger for ischemic stroke (especially cardioembolic, small-vessel occlusive, and very large artery atherosclerotic) compared with hemorrhagic stroke.
“Radon is an indoor air pollutant that can only be detected through testing that measures concentrations of the gas in homes,” Dr. Whitsel said in the release. “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 study lacked gender and racial/ethnic diversity, so the findings may not be generalizable to other populations.
“Replication studies of individual-level radon exposures are needed to confirm this positive radon-stroke association,” the authors write. “Confirmation would present a potential opportunity to affect public health by addressing a pervasive environmental risk factor for stroke and thereby merit reconsideration of extant radon policy.”
The study was funded by the National Institute of Environmental Health Sciences and National Heart, Lung, and Blood Institute. Dr. Whitsel and coauthors report no relevant financial relationships.
A version of this article appeared on Medscape.com.