New Study: This Increases Stroke Risk—and It’s Found in Almost 10% of Homes

Updated: Mar. 19, 2024

It's the second-leading cause of lung cancer behind smoking. Now researchers have narrowed in on another effect it may have on women's health.

If you’ve ever had to sell a home in an area with radon levels on the higher side, maybe your realtor suggested you open all the windows before the home inspection was done.

That’s good advice even when you’re not trying to sell your home. You may be aware of radon’s reputation as a factor leading to lung cancer—in fact, the United States Environmental Protection Agency (EPA) calls radon the second-leading cause of lung cancer, behind smoking.

Explains Eric A. Whitsel, MD, MPH, a professor of epidemiology and medicine at the University of North Carolina at Chapel Hill: “Radon is an indoor air pollutant that can only be detected through testing that measures concentrations of the gas in homes.” The Environmental Protection Agency calls radon a radioactive product of uranium and says radon can reach high levels in some homes, depending on the home’s construction and geology of the region where it’s located. Radon can seep into structures like homes, schools, and buildings through tiny openings in the floors and walls.

Radon is odorless, colorless, tasteless, and lurking in the ground beneath some homes, often in regions where coal mining was once an industry. The Environmental Protection Agency suggests “nearly one in 15 homes has a radon level that should be reduced.”

Now, Dr. Whitsel and his team have led a longitudinal study published in the peer-reviewed journal Neurology in February 2024, which found that radon may significantly elevate stroke risk for stroke—perhaps especially for middle-aged to older women. It’s been reported that strokes occur among 795,000 Americans each year, and the researchers noted that not a great deal is known about women’s stroke risk.

Notably, the study found that women living in areas with moderate to high radon levels faced higher stroke risk than those in regions with minimal radon exposure.

radon monitorBanksPhotos/getty images
A radon detector

Radon and stroke risk

Over 13 years, the research team followed the health outcomes of 158,910 women with an average age of 63. Initially, none of these participants had suffered a stroke; however, by the study’s end, 6,979 strokes had occurred within this group.

The researchers used the participants’ residential addresses to estimate their radon exposure per data from the U.S. Geological Survey and the EPA, who recommend keeping indoor radon levels below four picocuries per liter (pCi/L). The researchers note that four pCi/L is referred to as “the United States Environmental Protection Agency Radon Action Level for mitigation.” In other words, levels should fall under this point to be generally safe.

The study then divided participants into three groups based on radon exposure: High (above four pCi/L), intermediate (between two to four pCi/L), and low (below two pCi/L). The findings were telling: The group with the highest radon exposure experienced 349 strokes per 100,000 person-years, compared to 343 in the intermediate group and 333 in the lowest. (Note: Person-years is a calculation combining the count of participants and their total time spent in the study.)

After adjusting for other stroke risk factors, like smoking, diabetes, and high blood pressure, the highest-exposure group had a 14% increased risk of stroke. In comparison, the intermediate group had a 6% increase.

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How to respond to radon in the home

When radon concentrations reach or exceed four pCi/L, the EPA advises pursuing a radon mitigation system to reduce indoor levels by locating a certified contractor who specializes in this practice.

However, it’s important to note that the revelations from this study extend concerns to even lower radon concentrations. “We’ve identified a heightened risk of stroke in individuals exposed to radon levels up to two pCi/L below what’s currently considered the threshold for lung cancer prevention measures,” Dr. Whitsel reports.

He also recommends further research to validate these findings: “Confirmation would present an opportunity to improve public health by addressing an emerging risk factor for stroke.”

Environmental Protection Agency information last updated in October 2023 suggests that the areas where radon concentrations tend to be highest are in some Northeastern and Southeastern states (Appalachia is said to be one area most affected), as well as parts of the Midwest, Mountain states, Pacific Northwest, and Alaska. has listed the following as the 10 highest-radon states in the US, in this order:

  • Alaska – 10.7 pCi/L
  • South Dakota – 9.6 pCi/L
  • Pennsylvania – 8.6 pCi/L
  • Ohio – 7.8 pCi/L
  • Washington – 7.5 pCi/L
  • Kentucky – 7.4 pCi/L
  • Montana – 7.4 pCi/L
  • Idaho – 7.3 pCi/L
  • Colorado – 6.8 pCi/L
  • Iowa – 6.1 pCi/L

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