Background: Excessive arsenic intake has a detrimental effect on human health, as reflected in an increase in cancer incidence. In an area on the southwest coast of Taiwan, arsenic intake from well water since the 1920s had caused an exceptionally high mortality from cancer. Municipal water has become available to people living in the arseniasis endemic area since the early 1970s. This study explored the impacts of reduction in arsenic intake from water on lung cancer and bladder cancer in the arseniasis endemic area in Taiwan.

Methods: Chart records of 23,013 patients diagnosed with bladder cancer and 93,633 patients with lung cancer from 1979 to 2003 were retrieved from the Taiwan Cancer Registry Center. We used the age-period-cohort model to study the changes in the incidence of lung cancer and bladder cancer in the arseniasis endemic area and the rest of Taiwan.

Results: Three decades after municipal water supply to the arseniasis and black foot disease endemic area (BFDEA), we saw a marked decrease in the incidence of both bladder cancer and lung cancer in the area, especially for those in the later cohorts. The relative risk (RR) of getting a bladder cancer for people living in BFDEA when compared with those in the rest of Taiwan has dropped from 20 for the early cohorts to 5 for the late cohorts. As to lung cancer, the RR has decreased from 8 to between 1.5 and 2.

Conclusion: Reduction in arsenic intake from water has a positive impact on the incidence of both lung and bladder cancer; however, while RR for lung cancer has dropped to below 2, RR for bladder cancer remained at around 5. The difference may be because (1) there are other risk factors beside the well-water intake or (2) bladder cancer may have longer latency period for excessive arsenic exposure than lung cancer. More studies are required to understand the causes behind the difference in RR for these two types of cancer.