Radon, the naturally occurring radioactive gas seeping into millions of American homes, may pose a cancer risk far beyond the lungs. A first-of-its-kind study published in JAMA Network Open by University of North Dakota researchers reveals that women living in high-radon areas face a significantly elevated risk of developing ovarian cancer, with a 38% increased risk for the most common and lethal type (Source 1, 2).

The prospective cohort study analyzed data from over 127,000 postmenopausal women participating in the Women's Health Initiative over a 31-year period. Researchers linked the home addresses of 127,547 women to U.S. Geological Survey radon zone maps and tracked ovarian cancer cases and deaths over an average follow-up of nearly 18 years. The study observed 1,645 ovarian cancer cases and 1,048 ovarian cancer deaths during this time (Source 1, 2).

What Makes This Discovery Significant for Women's Health?

Ovarian cancer remains the fifth leading cause of cancer deaths among women in the United States, yet environmental risk factors have remained largely unknown. While genetic factors and reproductive history are well-established risk factors, this research provides the first individual-level evidence that radon exposure may be a modifiable environmental target for cancer prevention (Source 1, 2).

The findings were particularly striking for serous ovarian cancer, the most lethal and common type of ovarian cancer. Women in high-radon zones, defined as areas exceeding 4 picocuries per liter (pCi/L), had a 38% increased risk compared to those in low-radon zones with less than 2 pCi/L. Even more concerning, the risk of dying from ovarian cancer was 31% higher for women residing in high-radon zones (Source 1, 2).

"We have known for decades that radon is a leading cause of lung cancer, but its impact on other organs has been a subject of intense debate. This research provides the first individual-level evidence that the ionizing radiation from radon gas may be a target for mitigating ovarian cancer risk," said Mark R. Williamson, research assistant professor in the School of Medicine and Health Sciences Department of Population Health and lead author of the study.

Mark R. Williamson, Research Assistant Professor, University of North Dakota School of Medicine and Health Sciences

How Does Radon Reach Ovarian Tissue?

Radon is a naturally occurring radioactive gas produced by the decay of uranium in soil. It enters homes through foundation cracks and can accumulate to dangerous levels in basements and lower levels of buildings. While radon is primarily inhaled through the lungs, the gas is soluble in blood, meaning it can circulate throughout the body and reach internal organs (Source 1, 2).

The research team identified two potential biological mechanisms explaining how radon exposure might increase ovarian cancer risk. First, as radon decays, its radioactive byproducts may be carried to ovarian tissues through particulate air pollution, acting as a "Trojan horse" to deliver alpha-particle radiation directly to cells. Second, previous research has shown that radon inhalation can significantly increase levels of estradiol and other hormones in the blood, making radon a hormone disruptor with potential cancer consequences (Source 1, 2).

Steps to Reduce Your Radon Exposure at Home

• Get Your Home Tested: Only about 18% of U.S. homes have ever been tested for radon, despite approximately 25% of the population living in high-radon areas. The EPA recommends testing your home, especially if you live in a designated high-radon zone according to USGS maps.
• Install Radon Mitigation Systems: If testing reveals radon levels above the EPA action level of 4 pCi/L, professional radon mitigation systems can reduce indoor radon concentrations. These systems typically involve sub-slab depressurization or other ventilation techniques.
• Seal Foundation Cracks: Sealing cracks and gaps in your home's foundation, basement walls, and around pipes can reduce radon entry, though this alone is typically not sufficient to bring levels below the EPA action level.
• Improve Ventilation: Increasing air circulation in your home through proper ventilation can help reduce radon accumulation, particularly in basements and lower levels where radon concentrations tend to be highest.

"Residential radon is a ubiquitous exposure, but it is one we can control. If these findings are replicated, radon testing and mitigation could become a vital component of ovarian cancer prevention strategies," said Gary Schwartz, professor and chair of the School of Medicine and Health Sciences Department of Population Health and senior author on the study.

Gary Schwartz, Professor and Chair, University of North Dakota School of Medicine and Health Sciences Department of Population Health

What Are the Study's Limitations and Next Steps?

The researchers acknowledged important limitations in their work. The study focused exclusively on postmenopausal women, so findings may not apply to premenopausal women or men. Additionally, because radon exposure data was based on regional estimates from USGS maps rather than individual home tests, the results may not reflect actual personal exposure levels for every participant (Source 1, 2).

Despite these limitations, the research team is moving forward with additional investigations. Williamson and Schwartz are finalizing a radon test chamber at the University of North Dakota, one of only a few in the country, that will enable researchers to directly test the effects of radon on cells in laboratory settings. This facility will help confirm the biological mechanisms proposed in the epidemiological study (Source 1, 2).

The implications for public health policy could be substantial. If these findings are replicated in future studies, radon testing and mitigation could become standard recommendations for women at high risk for ovarian cancer. Additionally, building codes could be updated to require radon-resistant construction in new homes, particularly in high-radon areas, as a preventive health measure (Source 1, 2).

For the millions of Americans living in high-radon zones, this research underscores the importance of taking action on a modifiable environmental hazard. Unlike genetic risk factors for cancer, radon exposure can be detected and reduced through testing and mitigation, potentially preventing cases of ovarian cancer and saving lives.