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Radon was identified as a health problem when scientists noted that underground uranium miners who were exposed to it died of lung cancer at high rates. Results of miner studies have been confirmed by experimental animal studies, which show higher rates of lung tumors among rodents exposed to high radon levels.
Scientists agree that radon causes lung cancer in humans. Recent research has focused on specifying the effect of residential radon on lung cancer risk. In these studies, scientists measure levels in the homes of people who have lung cancer and compare them to the levels of radon in the homes of people who have not developed lung cancer.
One of these studies examined residential radon exposure in Iowa among females who had lived in their current home for at least 20 years. This study included 413 females with lung cancer and 614 females without lung cancer. During the study, radon levels were tested in homes, lung cancer tissues were examined, and the scientists collected information about home characteristics and other topics. Results from this study suggested a link between exposure to radon and lung cancer.
Scientists have conducted more studies like this in other regions of the United States and around the world. Many of these studies have demonstrated an association between residential exposure to radon and lung cancer, but this finding has not been observed in all studies. The inconsistencies between studies are due in part to the small size of some studies, the varying levels of radon in many homes, and the difficulty of measuring a person's exposure to radon over time.
Researchers have combined and analyzed data from all radon studies conducted in Canada and the United States. By combining the data from these studies, scientists were able to analyze data from thousands of people. The results of this analysis demonstrated a slightly increased risk of lung cancer associated with exposure to household radon. This increased risk was consistent with the level of risk estimated based on studies of underground miners.
Researchers are also investigating more precise ways to measure a person's exposure over time. In a study published in 2002, scientists examined radon exposure among people in Sweden who had not smoked daily for more than a year. This study included 110 people with lung cancer and 231 people without lung cancer. As with previous studies, the scientists measured radon levels of indoor air. The researchers also used a new technique of analyzing glass to estimate radon exposure over time. Using this technique, the scientists took measurements from glass in an object (for example, a mirror or picture frame) that was at least 15 years old and had been in the person's home throughout that time, even if the person had moved from one home to another. In this study, both of the techniques for measuring radon demonstrated a relationship between long-term exposure to radon and lung cancer, and supported the results of previous studies.