Epidemiological studies of nuclear power plants Epidemiology is a branch of science that identifies the impact that certain elements have on health, as well as their consequences on specific population groups. The results of epidemiological studies lead to actions that can improve health conditions in the populations subjected to the study. An epidemiological study consists of the observation of the frequency and distribution of a disease in a defined population group, for a specific time frame. It analyzes the cases presented or the mortality caused by the disease, as well as the factors that influence its development. The study is done in the natural environment of the observed individuals, and their life habits are taken into consideration. The procedure used in an epidemiological study is probabilistic in nature. Groups of people are selected. Over time, those who have suffered the effects of the variables in the study are identified. The frequencies of the diseases are determined. The results are then compared to studies on other groups with similar characteristics but not influenced by the variables under analysis. This procedure makes it possible to establish the incidence and corresponding effects on health of the considered events, as well as the necessary mechanisms for their control and treatment. Since the forties, hundreds of epidemiological studies have been carried out within the environments of nuclear power plants all over the world. Conducting epidemiological studies is not easy. It takes a lot of preparation, a precise identification of all the parameters that take place in the study and their interrelations, a detailed and in-depth study of the environmental conditions that might influencie the research, a prolongued observation time, orderly and thorough data collection, adequate means and properly trained specialists to correctly interpret and handle the data, the methods used and the reuslts obtained. The analyses of the effects of radiation at low doses are very hard to accomplish. Here are some of the reasons: Given their low incidence, the effects might be masked by causes other than radiation, which, at greater frequencies, could produce similar effects in an isolated or simultaneous way. From the methodolological and statistical viewpoint, and due to this low incidence, it is necessary to study very large population samples throughout several generations and along with very large contrast population samples (control samples) with similar environmental factors and which have not been exposed to the radiations. Humans are being continuously subjected to natural radiation (cosmic radiation and that of radioactive elements contained within the Earth's core) as well as artificial radiation (medical or industrial uses of nuclear energy, television, computers...), and for this reason there is a greater difficulty in discerning the effects produced by one or the other radiation sources. Epidemiological studies in Spain The latest study conducted in Spain is "Possible radiological impact of nuclear and radioactive sites on human health", done in co-operation with the Carlos III Health Institute. (It began in 2006 and the results were presented in May 2010). As a response to a social demand for the possible impact of nuclear and radioactive sites on human health, in 2005 Congress asked the Government to carry out and Epidemiological Study. For this reason, the Carlos III Health Institute, the Ministry of Science and Innovation and the Nuclear Safety Council (CSN) subscribed an cooperation agreement. The main goal was to research whether there is an effect from ionizing radiations derived from the operation of Spain's nuclear and radioactive sites involved in the nuclear fuel cycle on the health of the population living in the area, as well as in other areas where there are no such sites, but where the population is exposed to natural ionizing radiation at different levels. In September 2006, an Advisory Committee was created to guarantee a detailed and independent follow-up of this study as regards the scientific methodology applied and the disclosure of results. This Committee was formed by 25 members of the Health Departments from the autonomous communities affected by the territorial outreach of the sutdy, as well as syndicates, municipal authorities, site propietary companies, ecological groups and six independent epidemiology, radiology and radiological protection expert.s There were also representatives from the Carlos III Health Institute and CSN. The study included all the country's nuclear and radioactive sites, regardless of whether they are in operation, in definite shutdown or at the stage of dismantling. All the municipalities in a 30-km radius from each site were analyzed. For each plant, a sufficient number of municipalities located at a distance of 50 to 100 km (and not affected by its operation) were selected as a reference to compare cancer mortality n the municipalities that were subjected to the study. Two areas without nuclear sites and with different levels of natural radiation were analyzed. One is in Valencia, with very low levels, and the other in Galicia, with higher levels due to the granitic composition of its soil. Overall, 1,000 municipalities and over 8 million people were analyzed during the study's time span (from the start of operation of each plant until 2003). The study concluded that nuclear sites do NOT affect the population's risk of cancer. The result, presented in May 2010, is similar to results form other studies conducted in countries like the United States, France and England, and ratifies the previous study done by the Carlos III Health Institute in 1999. Among the most notable results are the fact that the estimated accumulated doses that the population would have received at the analyzed areas are very low. They are, on average, approximately 300 times lower than the natural radiation that is present around the sites. Likewise, they are significantly below levels that could be related to effects on human health. There has been no detection of an increase in cancer-related deaths associated to the operation of the sites. There has been no detection of an increase in cancer-related deaths due to natural radiation. International epidemiological studies The most thorough studies (carried out over long periods of time, on a large population sample, with a high number of controls, etcetera) indicate that operating nuclear power plants cause no negative incidence on health. The Office of Population Censuses and Surveys (OPCS) - United Kingdom (1959-1980) This study concluded that no increase of cancer was detected in nuclear power plants in England and Wales, particularly for those cases that are more frequently associated with radiation, such as leukemia, bonce cancer or multiple myeloma. Researchers analyzed eight million cases between 1959 and 1980. Tentencies in population health near nuclear power plants, United States (1997) Clifford H. Patrick presented the results of ten studies conducted by the Energy and Research Development Administration around the 104 nuclear power plants in the United States. The only study that presented negative results had several methodological limitations that made it impossible to coherently interpret the data. The study also included the results regarding population health around the Oak Ridge nuclear research center. They showed no negative effects on the population. Study by the National Cancer Institute - United States (1987-1990) The subjects of this study were 107 countries with or near to 62 nuclear power plants. The conclusion was that no evidence was found of any increase in mortality from cancer in any of the areas. Study by the Mailman School of Public Health at the University of Columbia - United States This study, which was published on November 2007 in the medical magazine Radiation Research, indicates that workers from the nuclear industry are less prone to dying of cancer and other diseases than the general population. This study was done on 53,000 workers from 15 nuclear power plants over an 18-year period between 1979 and 1997. The mortality rates in this group are 60% lower than in the general population with similar ages and characteristics. This is mostly due to the fact that professionally exposed workers must have good health and get annual medical checkups. The International Agency of Cancer Research in France has done studies on workers in the nuclear sector from 15 countries, to analyze the effects of exposure to low radiation doses and to contrast the conclusions from the Mailman School research. Some of the results show that the relationship between the development of leukemia and other cancers and the exposure to radiation doses "is insignificant and expected", a conclusion similar to that obtained from other epidemiological studies. University of Berne, Switzerland - September 2008 to December 2010 There is no relationship between juvenile cancer and Swiss nuclear reactors. This is the conclusion of a study conducted by the University of Berne by request from the Swiss medical authorities, which analyzed 1,3 million childern aged 0 to 15 and compared data from children born less than 5 km, 5 to 10 km and 10 to 15 km away from nuclear power plants to data from children born at a greater distance. Neither the cases found nor the annexed studies gave any indication of risks of leukemia or other forms of juvenile cancer as a result of living near nuclear power plants. There are 5 nuclear reactors in Switzerland (Beznau 1 and 2, Mühleberg, Gösgen and Leibstadt). Around 1% of the population lives less than 5 km away from a reactor, and 10% lives within a 15 km distance. The report from the University of Berne shows that, in the vicinity of the reactors, exposure to radiation surpasses exposure to natural radiation by 0,01milisievert per year. Port Hope Cohort Study - Canada (1969-1999) Canada has carried out several studies in nuclear environments to analyze the relationship between cancer and nuclear power plants or radioactive sites. One of the most extensive studies, named "Mortality (1950-1990) and Cancer Incidence (1969-1999) of Workers in the Port Hope Cohort Study Exposed to a Unique Combination of Radium, Uranium and Gamma-Ray Doses", was done on workers that were exposed to radium, uranium and X-rays at the Port Hope Community in Ontario, which houses Canada's only uranium conversion site, and where approximately 400 people work. The study reflects that, overall, these workers had a lower mortality and cancer rate than Canada's general population. Another study conducted in the same area between 1992 and 2007 shows that the incidence of cancers in Port Hope is similar to that of the population of Ontario and Canada with similar socio economic characteristics. Related questions: What is a radioactive source, and what is it for? What is radioactivity? How many applications does nuclear technology have?