Long-term tracking of nearly 160,000 people from across the United States suggests that brain cancer risk rises as exposure to radon increases.
The study led by Oregon State University scientists provides a look at the possible connection between radon, a known lung carcinogen, and cancers in other parts of the body.
Published in Neuroepidemiology, the research featured a cohort more than double the size of the only other previous examination of radon's potential link to central nervous system cancers, a 2013 study involving people in Denmark that produced similar findings.
The American study, led by OSU College of Health epidemiologist Matthew Bozigar and graduate student Carson Mowrer, used a geologically, geographically and environmentally diverse population to expand on the Danish research.
The cohort of 159,391 participants came from the Women's Health Initiative, a National Institutes of Health-funded project to explore ways to prevent heart disease, osteoporosis and cancer in postmenopausal women.
"Absolute risks of malignant central nervous system cancers rose with higher radon concentration across all metrics," Bozigar said.
Radon, a naturally occurring gas, is a product of the radioactive decay of uranium, which is present in certain rocks and soils. Upon escaping from the ground, radon itself decays and emits radioactive particles that can get within the body and collect in tissues, causing DNA damage that can lead to cancer.
Odorless, tasteless and colorless, radon dilutes quickly in open air and is generally harmless before it decays, but indoors or in areas with poor air exchange, it can easily concentrate and is recognized as a significant risk factor for lung cancer. Radon concentrations can be measured at low cost with small, passive detectors and mitigated through passive or active ventilation in basements and crawl spaces.
The Environmental Protection Agency says no level of radon exposure is safe and advises that mitigation efforts be taken when levels reach 4 picocuries per liter, and should be considered when they reach half that level; picocuries per liter is a unit for expressing the concentration of radioactive decay.
Cancers of the central nervous system are rare but highly deadly, he said, and their risk factors aren't well understood. The NIH predicts about 25,000 new cases in 2026 and, given a five-year survival rate of 33%, 18,000 deaths. The incidence rate is 6.1 cases per 100,000 people.
Following members of their Women's Health Initiative cohort for an average of about 18 years, the scientists identified 451 central nervous system cancer cases. They estimated radon exposure via data from the U.S. Geological Survey, the EPA and other sources.
"Our findings indicate residential radon exposure may contribute meaningfully to the overall burden of central nervous system cancers," said Mowrer, now a doctoral student at the University of North Carolina.
The National Institute of Environmental Health Sciences funded the research, which also included scientists from Harvard Medical School, Stony Brook University, the University of California San Diego, the University of North Dakota, State University of New York at Buffalo, and Fred Hutch Cancer Center.
