Archive for the ‘radiation hormesis’ Category
Case-control study of lung cancer risk from residential radon exposure in Worcester County, Massachusetts.
A few months ago, a rather interesting-sounding paper was published in Health Physics:
Case-control study of lung cancer risk from residential radon exposure in Worcester County, Massachusetts; Thompson et. al. Health Physics 94(3):228-241; 2008.
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.
The results of the study were described by their own authors as “surprising” and “stunning”: Clear evidence of radiation hormesis. It looks like Bernard Cohen has been vindicated after all.
“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.”
A study of lung cancer risk from residential radon exposure and its radioactive progeny was performed with 200 cases (58% male, 42% female) and 397 controls matched on age and sex, all from the same health maintenance organization. Emphasis was placed on accurate and extensive year-long dosimetry with etch-track detectors in conjunction with careful questioning about historic patterns of in-home mobility. Conditional logistic regression was used to model the outcome of cancer on radon exposure, while controlling for years of residency, smoking, education, income, and years of job exposure to known or potential carcinogens. Smoking was accounted for by nine categories: never smokers, four categories of current smokers, and four categories of former smokers. Radon exposure was divided into six categories (model 1) with break points at 25, 50, 75, 150, and 250 Bq m-3, the lowest being the reference. Surprisingly, the adjusted odds ratios (AORs) were, in order, 1.00, 0.53, 0.31, 0.47, 0.22, and 2.50 with the third category significantly below 1.0 (p < 0.05), and the second, fourth, and fifth categories approaching statistical significance (p < 0.1). An alternate analysis (model 2) using natural cubic splines allowed calculating AORs as a continuous function of radon exposure. That analysis produces AORs that are substantially less than 1.0 with borderline statistical significance (0.048 <= p <= 0.05) between approximately 85 and 123 Bq m-3. College-educated subjects in comparison to high-school dropouts have a significant reduction in cancer risk after controlling for smoking, years of residency, and job exposures with AOR = 0.30 (95% CI: 0.13, 0.69), p = 0.005 (model 1).
There is more discussion and commentary at PhysOrg, here.
It will be very interesting to keep an eye on research in this area in the future, especially given the famous debates between the likes of Bernard Cohen and William Field over their radon dose response research.