Authors?? Response

Abstract

To the Editor: We thank Lamm et al1 for responding to our article.2 They recalculated our data only for the period 1980–2000 (excluding 1971–1979) and this led to an estimate of similar significant negative slope for diabetes mellitus (DM) standardized mortality ratios (SMRs) for males and females. They dispute our conclusion that there is a gender difference in temporal pattern (only during the 1980s and 1990s). Because inorganic arsenic has been reported to be associated with an increased mortality from DM, it is logical to expect that a reduction of arsenic exposure through improvement in the water supply system would lead to a decrease in mortality rates from DM in both males and females living in the Blackfoot disease (BFD) endemic areas. We feel that their argument, however, provides further evidence that the association between arsenic exposure and DM was causal. Their point of criticism regarding the use of DM listed on the death certificate as the underlying cause of death has already been addressed in the discussion section of our article. We agree with Lamm et al that small numbers of DM deaths will provide much less stability to the analysis, particularly during the 1970s. To minimize this statistical variability, the 3-year moving averages of the SMR were calculated for this study. Lamm et al argue that fluorescent compounds (humic substances) in the artesian well water are a potential causative agent for BFD; thus, the decline in diabetes mortality may be the consequence of withdrawal of a water-borne factor, but whether arsenic is that factor is not clear. In our opinion, in the BFD endemic areas, the main exposure to inorganic arsenic is through ingestion of artesian well water containing high concentrations of arsenic. Physical and chemical characteristics of drinking water have been intensively studied in both BFD endemic and nonendemic areas.3 In artesian well water, the only chemical component exceeding the daily maximum allowable limit was arsenic. Although fluorescent compounds, known as humic substances, have been suggested to exert an initiator role in the development of BFD,4,5 there has been no epidemiologic evidence to show a correlation between exposure to humic substances and development of DM. The association between humic substances and BFD might be due to the confounding effect of an association between BFD and arsenic exposure.6 Thus, the reduction in DM mortality in the study area may result from the withdrawal of arsenic exposure through improvements in the water supply system as reflected by a change in water source. Hui-Fen Chiu, PhD Department of Pharmacology College of Medicine Kaohsiung Medical University Kaohsiung, Taiwan Chih-Ching Chang, MD, PhD Institute of Public Health College of Health Sciences Kaohsiung Medical University Kaohsiung, Taiwan Shang-Shyue Tsai, PhD Department of Healthcare Administration I-Shou University Kaohsiung County, Taiwan Chun-Yuh Yang, PhD, MPH Institute of Public Health College of Health Sciences Kaohsiung Medical University Kaohsiung, Taiwan