Long-Term Exposure to Arsenic in Community Water Supplies and Risk of Cardiovascular Disease among Women in the California Teachers Study

Background: Inorganic arsenic in drinking water (wAs) is linked to atherosclerosis and cardiovascular disease. However, risk is uncertain at lower levels present in US community water supplies (CWS), currently regulated at the federal maximum contaminant level of $10\mu g/L$.

Objectives: We evaluated the relationship between long-term wAs exposure from CWS and cardiovascular disease in the California Teachers Study cohort.

Methods: Using statewide health care administrative records from enrollment through follow-up (1995-2018), we identified fatal and nonfatal cases of ischemic heart disease (IHD) and cardiovascular disease (CVD). Participants' residential addresses were linked to a network of CWS boundaries and annual wAs concentrations (1990-2020). Most participants resided in areas served by a CWS (92%). Exposure was calculated as a time-varying, 10-year moving average up to a participant's event, death, or end of follow-up. Using Cox models, we estimated hazard ratios (HRs) and 95% confidence intervals (95% CIs) for the risk of IHD or CVD. We evaluated wAs exposure categorized by concentration thresholds relevant to regulation standards ($<1.00$, 1.00-2.99, 3.00-4.99, 5.00-9.99, $\ge 10\mu g/L$) and continuously using a log2-transformation (i.e., per doubling). Models were adjusted for baseline age, neighborhood socioeconomic status, race/ethnicity, body mass index (BMI), and smoking status. We also stratified analyses by age, BMI, and smoking status.

Results: Our analysis included 98,250 participants, 6,119 IHD cases, and 9,936 CVD cases. The HRs for IHD at concentration thresholds (reference, $<1\mu g/L$) were 1.06 (95% CI: 1.00, 1.12), 1.05 (95% CI: 0.94, 1.17), 1.20 (95% CI: 1.02, 1.41), and 1.42 (95% CI: 1.10, 1.84) for $1.00-2.99\mu g/L$, $3.00-4.99\mu g/L$, $5.00-9.99\mu g/L$, and $\ge 10\mu g/L$, respectively. HRs for every doubling of wAs exposure were 1.04 (95% CI: 1.02, 1.06) for IHD and 1.02 (95% CI: 1.01, 1.04) for CVD. We observed statistically stronger risk among those $\le 55$ vs. $>55$ years of age at enrollment ($p_{\text{interaction}}=0.006$ and 0.012 for IHD and CVD, respectively).

Discussion: Long-term wAs exposure from CWS, at and below the regulatory limit, may increase cardiovascular disease risk, particularly IHD. https://doi.org/10.1289/EHP14410.