Low-Level Radon Exposure May Reduce Lung Cancer Risk
Exposure to levels of radon gas typically found in 90 percent of American homes appears to reduce the risk of developing lung cancer by as much as 60 percent, according to a study published in the March issue of the journal Health Physics.
The finding differs significantly from the results of previous case-control studies of the effects of low-level radon exposure, which have detected a slightly elevated lung cancer risk (but without statistical significance) or no risk at all.
The study, undertaken jointly by researchers at Worcester Polytechnic Institute (WPI), Fallon Clinic, and Fallon Community Health Plan, is the first to observe a statistically significant hormetic effect of low-level radon exposure. Toxins and other environmental stressors (including radiation) that have a beneficial effect at very low doses are said to exhibit hormesis (scientists believe that the low doses of toxins may stimulate repair mechanisms in cells).
Home exposure to radon, a naturally occurring radioactive decay product of radium, has been thought to be the second leading cause of lung cancer, after cigarette smoking. Chemically inert, it can percolate out of the ground into basements.
The study was initiated and managed by Donald F. Nelson, now professor emeritus of physics at WPI, during the 1990s, a time when concern over the link between residential radon exposure and lung cancer was growing. Nelson says the aim was to try to establish what level of radon exposure actually correlated with significant lung cancer risk and to establish a safety zone for home radon levels. "We were certainly not looking for a hormetic effect," says co-author Joel H. Popkin of Fallon Clinic and St. Vincent Hospital in Worcester. "Indeed, we were stunned when the data pointed to that conclusion in such a strong way."
In the study, the exposure of 200 individuals with confirmed cases of primary lung cancer to radon was compared to the exposure of 397 carefully matched, randomly selected control subjects. All subjects were 40 years old or older and had lived in their homes for at least 10 years. All of the cases and controls were residents of Worcester County in Massachusetts and were enrolled in the same health maintenance organization, Fallon Community Health Plan.
The results were statistically adjusted for factors known to be correlated with lung cancer risk, including smoking, occupational exposure to carcinogens, and level of education. The adjusted results show that the odds ratios of developing lung cancer fall below one (the no effect level) at radon exposure levels within the range measured in about 90 percent of homes across the United States (0-150 Becquerel per cubic meter of air, or about 0-4 picoCuries per liter).
The U.S. Environmental Protection Agency recommends that homeowners take remediation actions when household radon exposure levels rise above 4 picoCuries per liter, based on the belief that radon exposure presents a linearly increasing lung cancer risk (a view not supported by the new study in the low-dose region).