Arsenic and Diabetes: Assessing Risk at Low-to-Moderate Exposures

Long-term exposure to inorganic arsenic through drinking water and food is known to cause skin lesions and carry an elevated risk of cancer, among other health effects.12 There is also evidence that high levels of exposure might increase an individual’s risk of type 2 diabetes. The connection is less clear at the low-to-moderate arsenic levels common in groundwater across the United States, but a prospective study in Environmental Health Perspectives takes a step toward clarifying the relationship. Once ingested, inorganic arsenic is metabolized into various organic compounds, including monomethylarsenate (MMA) and dimethylarsinate (DMA). The proportions of inorganic arsenic, MMA, and DMA in an individual’s urine can tell researchers something of the individual’s risk for certain diseases. The presence of a high percentage of MMA (indicating lower methylation capacity) is a risk factor for cardiovascular disease, skin and bladder cancers, and the skin lesions that characterize highly exposed individuals, whereas a high percentage of DMA (indicating greater methylation capacity) has been associated with increased risk of diabetes. Researchers led by senior author Ana Navas-Acien, a professor of environmental health sciences at Columbia University, assessed the relationship between arsenic exposure and incidence of type 2 diabetes among 1,838 American Indian men and women. The participants, members of the Strong Heart Family Study, lived in 12 communities in Arizona, Oklahoma, and North and South Dakota. American Indians are highly susceptible to type 2 diabetes due to a mix of genetic, lifestyle, and, potentially, environmental factors. The participants in this study had a median age of 36 years, allowing the researchers to assess the relationship between arsenic and type 2 diabetes early in the typical course of the disease. None of the individuals had diabetes at the start of the study. Baseline data were collected in 1998–1999 and 2001– 2004, with follow-up occurring in 2001–2004 and 2006–2009. To assess exposure, the researchers measured concentrations of different arsenic species in the participants’ urine. This approach has the benefit of capturing arsenic intake via both water and foods, including rice, other grains, and fruit juices, but it does not allow for direct comparison with regulatory guidelines for drinking water. Both the United States and the World Health Organization have adopted a drinking water standard of 10lg=L (10 ppb),19 but food levels currently are not regulated. The U.S. Food and Drug