Association between prolonged residential radon exposure and lung cancer risk

Two University of Iowa researchers were part of a large multi-center study that provides compelling direct evidence of an association between prolonged residential radon exposure and lung cancer risk.

The study, an analysis of data pooled from seven different North American residential radon studies, demonstrates an 11 to 21 percent increased lung cancer risk at average residential radon concentrations of approximately 3.0 picocuries per liter of air, during an exposure period of 5 to 30 years. The lung cancer risk increased with increasing radon exposure. The U.S. Environmental Protection Agency's current action level for residential radon is 4.0 picocuries per liter.

"This analysis, based on the largest radon data set assembled in North America, agrees with a similar large-scale radon pooled analysis performed concurrently in Europe. The North American and European pooling provides unambiguous and direct evidence of an increased lung cancer risk even at residential radon exposure levels below the U.S. EPA's action level," according to R. William Field, Ph.D., UI associate professor of occupational and environmental health and epidemiology, and a co-author of the study, which is reported in the March 2005 issue of the journal Epidemiology. Charles F. Lynch, M.D., Ph.D., professor of epidemiology, also contributed to the research.

Radon is the second-leading cause of lung cancer in the United States with an estimated 21,000 lung cancer deaths each year related to radon exposure, according to EPA. A radioactive, invisible, odorless gas that comes from the decay of naturally occurring uranium in the earth's soil, radon can accumulate in enclosed areas, such as underground mines and homes.

The initial link between radon exposure and lung cancer had been derived from studies of underground miners, who are exposed at much higher levels to the radioactive gas, and from animal and in vitro studies. Some previous case-control studies reported a positive or weakly positive association between lung cancer risk and residential radon concentrations, while others found no evidence of an association. The North American pooling study was designed to assess the seemingly disparate findings from these earlier studies.

Field and Lynch were part of an international team of researchers who performed the combined analysis of the original residential radon studies, conducted in Connecticut, Iowa, New Jersey, Missouri, and Utah and South Idaho, as well as Winnipeg, Canada. The original studies were funded from several federal sources, including the National Institute of Environmental Health Sciences and the National Cancer Institute. The investigators' review of 3,662 cases and 4,966 controls from these combined studies represents the largest analytic radon epidemiologic study ever performed in North America.

"The findings from the previously performed Iowa Residential Radon Lung Cancer Study indicate the risk estimates from this pooled analyses actually may slightly underestimate the true risk posed by prolonged residential radon exposure," Field said, noting potential exposure misclassification resulting from the pooling techniques. Investigators are currently pooling the results from the North American and European studies.