Water Arsenic Levels and Breast Cancer Risk in a United States-Wide Prospective Cohort.
TL;DR
Levels of arsenic in water in the U.S. may contribute to breast cancer risk, a suggestive positive association between relatively higher water arsenic levels and breast cancer incidence is observed; however, the non-monotonic trends and exposure assessment limitations warrant further investigation.
Abstract
In the U.S., drinking water is an important source of exposure to inorganic arsenic, an established human carcinogen. Chronic exposure to low levels of inorganic arsenic (≤10 μg/L) has been linked to bladder and kidney cancers; however, the association with other cancers remains inconsistent. We investigated the association between arsenic from private wells and community water systems and breast cancer incidence in a large U.S.-wide prospective cohort. Among 33,864 Sister Study participants residing in states with available arsenic data and reporting eligible water source types at enrollment (2003-2009), geocoded residential addresses were linked to county-level water arsenic concentrations. For community water system (CWS) users (n=27,290), addresses were linked to county-level water arsenic concentrations using the EPA National Contaminant Occurrence database (2006-2008). For well water users (n =6,574), addresses were linked to county-level modeled probabilities that arsenic levels in private well water exceeded 10 μg/L. Cox proportional hazards regression was used to estimate adjusted hazard ratios (HR) and 95% confidence intervals (CI) for the association between water arsenic and incident breast cancer, with subgroup analyses by tumor subtypes and menopausal status. Over 13.2 years (mean) of follow-up, 3,309 breast cancer cases (invasive and ductal carcinoma in situ) were diagnosed. We observed non-monotonic but elevated associations between increasing levels of water arsenic and invasive breast cancer risk (CWS HRQ5vsQ1=1.11, 95%CI 0.98-1.27, P-trend=0.16; Well HRQ5vsQ1=1.11, 95%CI 0.84-1.47, P-trend=0.88). When stratified by hormone receptor status and menopausal status, the associations did not meaningfully differ between subgroups. In a nationwide prospective cohort, we observed a suggestive positive association between relatively higher water arsenic levels and breast cancer incidence; however, the non-monotonic trends and exposure assessment limitations warrant further investigation. These results suggest that levels of arsenic in water in the U.S. may contribute to breast cancer risk.