LAUSR

To the Editor: Inorganic arsenic (i-As) is an established human bladder carcinogen.1 Generally, diet is considered the primary source of i-As for the United States and other populations around the world with access to relatively low arsenic drinking water.2,3 Ingested i-As from rice is estimated to dominate the exposure.2 Thus, we hypothesized that rice consumption may be related to bladder cancer incidence. Bladder cancer is a common malignancy in the United States, and elevated bladder cancer incidence and mortality rates are reported in northern New England, largely attributed to drinking arsenic-contaminated water from private unregulated wells.4 To date, very little epidemiologic research exists on the potential oncogenic role of rice as a source of i-As exposure.5 As part of a US population-based case–control study of bladder cancer, we assessed the association between rice intake and bladder cancer incidence. Using adjusted logistic regression models, we estimated the odds ratios (OR) and 95% confidence intervals (CI) for rice consumption overall, by rice type (i.e., polished/white or brown rice), and rice consumption level (i.e., ≤20 or >20 g/day), and stratified by household tap water arsenic (i.e., <1 or ≥1 μg/L) (Table and eTable 2; http://links.lww.com/EDE/B442). Our study population provided informed consent in accordance with the Committee for the Protection of Human Subjects at Dartmouth College. The population comprised bladder cancer cases (n = 316) identified through the New Hampshire State Department of Health and Human Services’ Cancer Registry and controls (n = 230) selected from lists of New Hampshire residents obtained from the New Hampshire Department of Transportation (<65 years) and Medicare enrollment lists (≥65 years).6 We used a validated food frequency questionnaire that covered participants’ diets during the past year to assess rice consumption (eFigure 1; http://links.lww.com/ EDE/B442). Further details about the study population are also available in the eTable 1 (http://links.lww.com/EDE/B442). Overall, 72% of cases and 78% of controls reported rice consumption (OR = 0.8, 95% CI = 0.5, 1.3). However, among those with higher water arsenic, the odds ratio was somewhat elevated (OR = 1.3, 95% CI = 0.4, 3.5) and similar to that reported previously5 but with limited statistical precision. Indeed, to our knowledge, the only prior study that investigated the relation between bladder cancer risk and rice consumption reported a pooled relative risk of 1.3 and 95% CI = 1.0, 1.8 for rice consumed ≥5 times per week compared with rice consumed <1 per week among women from the Nurses’ Health Study and men from the Health Professionals Follow-up Study.5 Our study found evidence of an interaction between brown rice consumption and water arsenic concentrations particularly for high consumers of brown rice (P = 0.003; eTable 2; http://links.lww.com/EDE/ B442). Overall, brown rice consumption was associated with an elevated odds ratio among those with greater than 1 μg/L water arsenic (OR = 2.3, 95% CI = 0.6, 9.3), but again with wide confidence intervals (Table and eTable 2; http://links.lww.com/EDE/ B442). A conceivable explanation for our findings could be related to the typically higher i-As content of brown rice compared with white rice and, the potential increase of i-As burden in cooked rice if arsenic-contaminated cooking water is used.2,7 While our findings do not provide clear evidence that rice contributes to the overall incidence of bladder cancer, the potential risk of brown rice consumption in the presence of elevated water arsenic warrants further investigation in larger studies.