High and low doses of ionizing radiation elicit opposite effects.
Low doses stimulate physiologic functions in humans and experimental animals.
The epidemiologic evidence reviewed here shows reduced total cancer mortality rates in exposed nuclear workers and other populations. The above results are supported by information from a variety of exposed populations. Although exposed to 2-6 Gy from a rain of fallout for four hours from a hydrogen bomb explosion in 1954 at Bikini Island, none of the 23 Japanese fishermen died from cancer within 25 years. Increased leukemia has not been found in the exposed population within these 10 years. The principle mechanism appears to be increased immune competence.