There are no increased adverse health effects in high background area studies in addition to US and Guangdong China studies. She notes that Down's syndrome in Kerala is slightly lower than the rate in India. Dr. Yalow also notes that in Guarapari Brazil, at 6 times the background dose rate, no adverse health effects are found, and that studies of numerous other small populations that live at relatively high natural radiation dose rates, equivalent to living in areas with extremely large radioactivity releases from facilities or radioactive waste disposal sites.
None find adverse health effects associated with significant increases in radiation doses.