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Radon Exposure and Incident Stroke Risk in the Women's Health Initiative
Sophie F Buchheit1, Jason M Collins1, Kurtis M Anthony1
1From the Brown University (S.F.B.), Providence, RI; Family Medicine (S.F.B.), Mountain Area Health Education Center, Asheville, NC; Department of Epidemiology (J.M.C., K.M.A., S.-A.M.L., J.D.S., R.G., E.A.W.), Gillings School of Global Public Health, and Department of Neurology (D.Y.H.), School of Medicine, University of North Carolina, Chapel Hill; Department of Medicine (J.E.M.), Brigham and Women's Hospital, Harvard Medical School, Boston, MA; Division of Public Health Sciences (A.P.R.), Fred Hutchinson Cancer Research Center and Department of Epidemiology, University of Washington, Seattle; Department of Population Health (G.G.S.), School of Medicine & Health Sciences, University of North Dakota, Grand Forks; Department of Epidemiology and Prevention (M.Z.V.), Wake Forest School of Medicine, Winston-Salem, NC; Geosciences and Environmental Change Science Center (R.R.S.), U.S. Geological Survey, U.S. Department of the Interior, Denver, CO; Department of Statistics & Operations Research and Department of Biostatistics (R.L.S.), Gillings School of Global Public Health, and Department of Medicine (E.A.W.), School of Medicine, University of North Carolina, Chapel Hill.
Background And Objectives:
Little is known about the role of radon in the epidemiology of stroke among women. We therefore examined the association between home radon exposure and risk of stroke among middle-aged and older women in the United States.
Methods:
We conducted a prospective cohort study of postmenopausal women aged 50-79 years at baseline (1993-1998) in the Women's Health Initiative. We measured exposures as 2-day, indoor, lowest living-level average radon concentrations in picocuries per liter (pCi/L) as estimated in 1993 by the US Geological Survey and reviewed by the Association of American State Geologists under the Indoor Radon Abatement Act. We used Cox proportional hazards models to estimate risk of incident, neurologist-adjudicated stroke during follow-up through 2020 as a hazard ratio and 95% CI, adjusting for study design and participant demographic, social, behavioral, and clinical characteristics.
Results:
Among 158,910 women without stroke at baseline (mean age 63.2 years; 83% white), 6,979 incident strokes were identified over follow-up (mean 13.4 years). Incidence rates were 333, 343, and 349 strokes per 100,000 woman-years at radon concentrations of <2, 2-4, and >4 pCi/L, respectively. Compared with women living at concentrations <2 pCi/L, those at 2-4 and >4 pCi/L had higher covariate-adjusted risks of incident stroke: hazard ratio (95% CI) 1.06 (0.99-1.13) and 1.14 (1.05-1.22). Using nonlinear spline functions to model radon, stroke risk was significantly elevated at concentrations ranging from 2 to 4 pCi/L (p = 0.0004), that is, below the United States Environmental Protection Agency Radon Action Level for mitigation (4 pCi/L). Associations were slightly stronger for ischemic (especially cardioembolic, small vessel occlusive, and large artery atherosclerotic) than hemorrhagic stroke, but otherwise robust in sensitivity analyses.
Discussion:
Radon exposure is associated with moderately increased stroke risk among middle-aged and older women in the United States, suggesting that promulgation of a lower Radon Action Level may help reduce the domestic impact of cerebrovascular disease on public health.
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