In 1963, the U.S. and the Soviet Union halted atmospheric testing due to worries over fallout, after widespread exposure to radiation in fallout. According to a 2002 study by the U.S. National Center for Environmental Health, almost all Americans born since 1951 carry radioactive contamination from aboveground nuclear bombs tests. The report blamed very roughly 11,000 cancer deaths on the fallout.
The fallout, from more than 400 Cold War atmospheric bomb tests, include the radioactive isotopes strontium 90, which bonds to bones, and iodine 131, which causes thyroid cancer. A previous study by the National Cancer Institute estimated that 11,300 to 212,000 thyroid cancers resulted from atmospheric testing. Most thyroid cancers are curable.