What did we learn from epidemiological studies in high background radiation area in India

Cancer causing potential of chronic exposure to high natural radiation seen in Chavara-Neendakara coast of Karunagappally taluk in Kerala, India is studied by the Natural Background Radiation Cancer Registry, Karunagappally since 1990. Population survey of 359,619 people recorded socio-demographic (SD) information and radiation levels measured inside (71,674) and outside (76,942) houses. Radiation level between and within the panchayats showed large variations. About 23,000 population were exposed to >4 mSv. Cancer pattern and trends were examined in relation to radiation levels. During 1990-2000 lung cancer was the predominant cancer among males (age adjusted rates (AAR) −18.2), followed by esophagus (AAR −6.3). Among females, cancers of the breast (AAR −14.3), cervix (AAR −13.4) and thyroid (AAR −4.3) were the major cancers. Only marginal differences in cancer incidence and its pattern were seen in different areas when broadly classified according to radiation level zones. Increase of incidence of lung cancer with radiation was seen among males but not in females. This needs in-depth studies. Role of confounding and competing risk factors need to be assessed with larger data sets.