Incidence of cancer among population utilizing geothermal hot water: A census based cohort study

Background/Purpose: Residents in high temperature geothermal areas have higher incidence of cancers than others due to increased incidence of non-Hodgkin lymphoma, breast, and pancreas cancers. The aim was to assess whether utilization of geothermal hot water for heating and washing is associated with risk of cancer. Methods: The data source was the census from 1981. Personal identifier of those 5-65 years of age was used in record linkage with nation-wide death and cancer registries. Thus, vital and emigration status was ascertained and cancers cases identified. The exposed population was defined as inhabitants of communities with geothermal hot-water supply generated from geothermal wells since 1972. Reference populations were inhabitants of other communities on areas with different degree of volcanic/geothermal activity. Hazard ratio (HR) and 95% confidence intervals (CI) were estimated in Cox-model. Results: Adjusted HR in the hot-water supply areas for all cancer was 1.11 (95%CI 1.03-1.20) as compared with cold area. The HR for breast cancer was 1.26 (1.04-1.52), prostate cancer 1.36 (1.13-1.64), kidney cancer 1.49 (1.07-2.08), and for basal cell carcinoma (BCC) of the skin 1.38 (1.14-1.68). Positive exposure-response relations were observed between these cancers and the degree of volcanic/geothermal activity in the reference areas. The HRs for single cancer site were never significantly lower than unity. Conclusion: The increase of breast cancer and BCC is consistent with previous findings in high temperature geothermal areas. Data on reproductive factors do not explain the increased risk of breast cancer. More precise information on exposure is needed in further studies.