Consumption of White Rice and Brown Rice and Urinary Inorganic Arsenic Concentration

To the Editor: Existing data have suggested that rice intake was associated with elevated urinary excretion of total arsenic among pregnant women1 and in a population in Bangladesh whose major staple food is rice.2 Moreover, evidence suggests that brown rice may contain more arsenic than white rice.3 In this research, we aimed to examine brown and white rice consumption in relation to urinary excretion of arsenic among US adults. The study population consisted of 6,677 US adults (≥20 years) in the 2003–2010 National Health and Nutrition Examination Survey, who were randomly selected for urine arsenic analysis. Arsenic species were separated using high-performance liquid chromatography. Because inorganic arsenic, i.e., arsenous acid and arsenic acid, had low detection rates (<5%), we derived inorganic arsenic excretion by subtracting most abundant organic arsenic, i.e., arsenobetaine, from the total arsenic concentration.4 We calculated average white rice and brown rice intake assessed using two nonconsecutive 24-hour recalls. The first recall was done during an in- person interview, and the second recall was conducted through a telephone interview 3–10 days later.5 In statistical analysis, we log-transformed excretion of arsenic and used generalized linear models to compare the urinary arsenic concentration in white- and brown-rice eaters. We took into account the sampling weights specifically for participants included in the arsenic assessments. We used SAS 9.3 (SAS Institute Inc., Cary, NC) to perform statistical analysis. We observed that intakes of white and brown rice were both associated with higher total urinary arsenic concentrations, and the inorganic arsenic concentrations were not different between participants who primarily ate white rice versus those who ate brown rice: as shown in Figure the geometric mean ± SE of inorganic arsenic were 7.93 ± 0.24 μg/L for participants who did not eat rice (n = 5,443), 11.51 ± 0.49 μg/L for those who ate <1 cup/day white rice only (n = 562), and 13.06 ± 0.56 μg/L for those who ate ≥1 cup/day white rice only (n = 505; Ptrend < 0.001). For brown-rice eaters, the means were 10.92 ± 1.07 μg/L for those who ate <1 cup/day brown rice only (n = 73) and 13.05 ± 1.25 μg/L for those who ate ≥1 cup/day brown rice only (n = 67; Ptrend <0.001). There are only 27 participants who reported consuming both white rice and brown rice (mean total rice intake = 2.14 cup/day), and the geometric mean ± SE of their inorganic arsenic were 15.90 ± 2.38 μg/L. Urine excretion of total arsenic and inorganic arsenic by participants’ characteristics are presented in eTable 1 (https://links.lww.com/EDE/A961)FIGURE: Data are geometric means (in μg/L), adjusted for age (years), gender (male/female), race/ethnicity (white/black/Mexican American/others), body mass index (kg/m2), education (less than high school/high school/higher than high school), smoking status (never smoked/former smoker/current smoker), and urine creatinine level (mg/dl). Sample size in each category: never eat rice (n = 5,443); white rice only, <1 cup/day (n = 562); white rice only, ≥1 cup/day (n = 505); brown rice only, <1 cup/day (n = 73); brown rice only, ≥1 cup/day (n = 67); and eat both white and brown rice (n = 27).To the best of our knowledge, this study compared for the first time the two main types of rice, i.e., brown versus white rice, in terms of their contributions to inorganic arsenic exposures. Arsenic is primarily localized in outer layers of the grain.3 As a result, brown rice grains typically have higher arsenic levels than polished white rice.6 Jackson et al.7 recently reported a high inorganic arsenic concentrations in organic brown rice syrup. In this study, however, we did not observe a difference in urinary excretion of inorganic arsenic between participants who primarily ate brown rice and those who primarily ate white rice, although the number of brown-rice eaters was relatively small. One explanation for this finding is that the 2-day recalls may not be able to capture the long-term rice consumption. In addition, the outer layer part of rice grain, i.e., the pericarp and aleurone layer, which are removed during polishing process, makes up only a minor part of the grain (approximately 14%). Thus, at the same intake amount, the relative differences in arsenic concentrations between brown and white rice are less than those between bran per se and white rice.8 In summary, we found that consumption of white and brown rice showed similar associations with inorganic arsenic in urine. Data from prospective studies with larger sample size of rice eaters are needed to verify our findings. Hongyu Wu Department of Nutrition Harvard T.H. Chan School of Public Health Boston, MA Philippe Grandjean Department of Environmental Health Harvard T.H. Chan School of Public Health Boston, MA Institute of Public Health University of Southern Denmark Odense, Denmark Frank B. Hu Departments of Nutrition and Epidemiology Harvard T.H. Chan School of Public Health Boston, MA Channing Division of Network Medicine Department of Medicine Brigham and Women’s Hospital and Harvard Medical School Boston, MA Qi Sun Department of Nutrition Harvard T.H. Chan School of Public Health Boston, MA Channing Division of Network Medicine Department of Medicine Brigham and Women’s Hospital and Harvard Medical School Boston, MA. [email protected]