Prospective cohort study of radon exposure and thyroid cancer risk in the Women’s Health Initiative

Exposure to ioninzing radiation during youth is an established risk factor for thyroid cancer but whether exposure during adulthood increases risk is unclear. The major source of ionizing radiation for most individuals is radon gas at home. Analysis of postmenopausal women in the Women’s Health Initiative examined the association between residential radon exposure and incident thyroid cancer. Information on household radon concentrations was obtained from the 1993 US Geological Survey. Among 158,770 women without thyroid cancer at baseline, 521 incident thyroid cancers were observed over a mean follow-up of 17.7 years. Incidence rates were 18.5, 18.2, and 19.5 cancers per 100,000 women-years at radon concentrations of <2, 2-4, and > 4 pCI/L, respectively. After adjustment for covariats, women living at concentrations of 2-4 and > 4 pCi/L did not have higher hazards of thyroid cancer compared to women living at < 2 pCI/L: HR 0.99 (95% CI 0.80-1.23) and 0.92 (95% CI 0.70-1.21), respectively. The authors conclude that these results suggest that residential radon exposure during adulthood does not appear to be associated with risk of incident thyroid cancer among postmenopausal women.