Scientists say that exposure to low levels of radon gas, which generally percolates out of the ground into basements, seems to reduce the risk of developing lung cancer by about 60 per cent.
This inference is based on the observations made during a study by experts at Worcester Polytechnic Institute, Fallon Clinic, and Fallon Community Health Plan.
The researchers say that the levels of exposure that appeared to reduce the risk of lung cancer in the study, involving about 600 Massachusetts homes, were nearly the same as typically found in 90 per cent of American homes.
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 or no risk at all.
It is significant due to the fact that home exposure to radon has been thought to be the second leading cause of lung cancer, after cigarette smoking.
A paper describing their study, published in the journal Health Physics, says that it was for the first time during the instant study that a team of researchers observed a statistically significant hormetic effect of low-level radon exposure.
Lead researcher Donald F. Nelson, Emeritus professor of Physics at WPI, initiated and managed the study amid growing concern over the suggested link between residential radon exposure and lung cancer.
He says that the main purpose of the study was to determine what level of radon exposure actually correlated with significant lung cancer risk, and to establish a safety zone for home radon levels.
Joel H. Popkin of Fallon Clinic and St. Vincent Hospital in Worcester, who jointly authored the study with Nelson, says: "We were certainly not looking for a hormetic effect. Indeed, we were stunned when the data pointed to that conclusion in such a strong way."
During the study, the research team calculated radon levels by installing radon monitors in areas of the home where the subjects spent the most wakeful time, in the subjects' present and former bedrooms, and other areas where the subjects spent as little as one hour per week.
The subjects' exposures were then obtained by weighting the measurements according to the time typically spent near each detector.
The study's results were adjusted to account for how subjects' home use changed with changing lifestyle, such as transitioning from full-time employment to retirement.
"Our analysis shows this to be an important improvement over exposure measures used by almost all other studies," said Nelson.
He, however, cautioned that the findings should not be taken to be as suggesting that even higher levels of radon exposure were safe.
"It is important to note that these new results do not dispute the lung cancer risk associated with higher levels of radon exposure experienced by uranium miners. Nevertheless, the results represent a dramatic departure from previous results and beliefs. Of course, a single epidemiological study is seldom regarded as definitive, so our results point to the need for new studies using our techniques," Nelson said.