I have been told numerous times that "People in naturally high background radiation areas in the world suffer no ill effect from the high radiation." I just stumbled upon one study in 2004 on such areas in Brazil.
Conclusion of this particular study: Cancer mortality in "Poços de Caldas, and Guarapari is higher than would be expected for their respective reference population", whereas "cancer mortality for the Araxá population is lower than would be expected".
International Congress Series
Volume 1276, Pages 3-468 (February 2005)
High Levels of Natural Radiation and Radon Areas: Radiation Dose and Health Effects, Proceedings of the 6th International Conference on High Levels of Natural Radiation and Radon Areas, Osaka, Japan
6–10 September 2004
Edited by T. Sugahara, H. Morishima, M. Sohrabi, Y. Sasaki, I. Hayata and S. Akiba
Pattern of cancer mortality in some Brazilian HBRAs
Lene H.S. Veiga, Sérgio Koifman
Among residents of Brazilian High Background radiation Areas, there is great concern about radiation-related health effects and there is also a common certitude that cancer incidence is higher in those areas than in other Brazilian areas with normal background radiation. This paper aims to present an overview of Brazilian High Background Radiation Areas and evaluate whether cancer mortality among residents from Poços de Caldas, Araxá, and Guarapari is higher than would be expected when applying mortality rate of their respective States. Results show that cancer mortality from the Brazilian HBRAs, Poços de Caldas, and Guarapari is higher than would be expected for their respective reference population. On the other hand, cancer mortality for the Araxá population is lower than would be expected.