Residential radon exposure shows no link to thyroid cancer in large US women’s cohort

Residential radon exposure during adulthood does not appear to raise the risk of thyroid cancer among postmenopausal women, according to a prospective analysis of the Women’s Health Initiative published in BMC Cancer. The finding challenges a plausible but untested concern, because ionizing radiation during youth is an established thyroid cancer risk factor, while the role of adult exposure has remained unclear.

Radon is a radioactive gas that constitutes the major source of ionizing radiation for most people, and it accumulates in homes. To test whether this everyday exposure matters for thyroid cancer, researchers linked household radon concentrations from the 1993 US Geological Survey, measured in picocuries per liter, to health outcomes in a cohort of postmenopausal women followed through 2024.

The study included 158,770 women who were free of thyroid cancer at baseline. Over a mean follow-up of 17.7 years, 521 incident thyroid cancers were observed. Incidence rates were remarkably similar across exposure categories: 18.5 cancers per 100,000 woman-years at radon concentrations below 2 pCi/L, 18.2 at 2 to 4 pCi/L, and 19.5 above 4 pCi/L.

After adjustment for study design and demographic, social, behavioral, and clinical characteristics, women living at concentrations of 2 to 4 pCi/L did not have a higher hazard of thyroid cancer than those living below 2 pCi/L, with a hazard ratio of 0.99 (95% confidence interval 0.80 to 1.23). Women at the highest category, above 4 pCi/L, likewise showed no elevated hazard, with a hazard ratio of 0.92 (95% confidence interval 0.70 to 1.21). Both intervals include the null value of 1.0, indicating no detectable association.

Sensitivity analyses using alternative approaches to radon measurement produced similar results, suggesting the conclusion is not an artifact of one particular exposure assessment method. The authors note that exposure misclassification could have influenced the findings, a common limitation when estimating long-term residential exposure from survey-based radon maps rather than individual home measurements.

Because the cohort consisted of postmenopausal women in the United States, the results apply to middle-aged and older women and cannot be extended to men, younger adults, or populations with different radon levels. The prospective design, large sample size, and long follow-up strengthen the evidence, but the study addresses adult exposure only and cannot speak to the well-established risks of radiation exposure during childhood and adolescence.

Subject of Research: The association between residential radon exposure and thyroid cancer risk in postmenopausal women

Article Title: Radon and thyroid cancer risk in the Women’s Health Initiative

Article References: Williamson, M. R., Whitsel, E. A., Collins, J. M., Stewart, J. D., Smith, R. L., Siezaga, J., Manson, J. E., Meliker, J. R., Wallace, R. B., Ryu, R. H., & Schwartz, G. G. (2026). Radon and thyroid cancer risk in the Women’s Health Initiative. BMC Cancer. https://doi.org/10.1186/s12885-026-17287-2

Image Credits: AI Generated

DOI: 10.1186/s12885-026-17287-2

Keywords: radon, thyroid cancer, Women's Health Initiative, ionizing radiation, prospective cohort, hazard ratio, residential exposure, postmenopausal women, US Geological Survey, epidemiology, thyroid, cancer