Natural Background Radiations, Radioadaptive Response and Radiation Hormesis

Natural background radiation has been an interesting subject among scientific studies for many years. The effective radiation dose of human from natural sources is about 2.5 mSv/y but it is higher in some regions of the world. Ramsar in Mazandaran, Iran is one of the most important areas and it has the highest natural background radiation among whole residential areas of the world. Background radiation is an ionizing radiation in the environment that its source could be natural or man-made. Its natural sources are cosmic radiations, terrestrial radiation, internal radiation and radon and its man-made sources could be the nuclear power plants and the scatter radiations of atomic bomb tests. There are a lot of studies about the effects of natural background radiation on the biological systems and even humans. Most of these studies confirmed the harmless and even useful effects of the certain doses of natural background radiation. Also there are reports on the decrease, increase or even equality in risk of some cancers between low and high doses of radiation. Nevertheless extensive epidemiological studies are needed to confirm the effect of low dose radiation on carcinogenesis and other factors and even decrease or increase of the risk in different types of cancers is possible too.