Revision 1
March 19, 1998
by Radiation, Science, and Health, Inc.,
Edited by J. Muckerheide

1.2.6.3
Radon

1.2.6.3.3
Case-Control Studies

"The negative correlations of home radon levels with lung cancer rates ... are based on ecological studies on groups of people; they can be taken as strong evidence against the validity of non-threshold hypothesis that is adopted for the assessment of radiation risk by the EPA and corresponding agencies in many other countries in the world. The question of whether there is causal relationship between risk of lung cancer and exposure to natural radon cannot, however, be answered by ecological studies because it is conducted on groups of people rather than on individuals. ... (B)ut recently Blot et al. (1990) conducted a case-control study on lung cancer patients in China, measuring radon levels in their dwellings.

"Application of a modern diagnostic method within a study of Chinese residents with high population stability was considered to allow precise information on health problems. The study comprised 308 eligible lung cancer patients, who were female residents of Shenyang in the age range 30-96 years and in whom primary lung cancer had been diagnosed in 1985-1987.... (A)ll suspected cases of lung cancer and supporting diagnostic materials were reviewed and classified by an expert panel of pulmonary disease physicians and pathologists. As a control group, 356 healthy female residents of Shenyang were randomly selected to match the age distribution of the cases.

"Radon was measured ... in the houses of patients and controls for one year; two detectors were placed in each house, one in the bedroom and the other in the living room. ...The median levels were 2.8 pCi/L in the houses of patients and 2.9 pCi/L in the houses of control subjects.

"Except for a slight, non-significant upward trend for small-cell carcinoma, no evidence of increasing risk with increasing radon level was found. On the contrary, a downward trend in cancer risk with increase in indoor radon levels was seen, which was clearer for adenocarcinoma than for squamous-cell carcinoma. According to Blot et al. (1990), if the no-threshold hypothesis of the BEIR-IV Report (1988) were true, an odds ratio of 1.8 would be found for lung cancer with exposure to a radon level >8 pCi/L in comparison with the level 0.1-1.9 pCi/L; this value is significantly higher than the observed ratio 0.7, with an upper confidence limit of 1.3. The currently adopted no-threshold hypothesis thus overestimates the risk represented by radon."