MORTALITY AND CANCER INCIDENCE IN MISASA, JAPAN, A SPA AREA WITH ELEVATED RADON LEVELS

A historical cohort study was conducted in Misasa town, Tottori prefec ture, Japan, where radon spas have been operating for a long time. Mis asa town was divided into an elevated radon level area and a control a rea, with mean indoor radon levels of about 60 and 20 Bq/m(3), respect ively. In total, 3,083 subjects in the elevated radon level area and 1 ,248 in the control area, all aged 40 or older on January 1, 1976, wer e followed up until December 31, 1993, for a mean period of 14 years, The mortality rates from all causes exhibited no difference between th e elevated radon level area and the control area for both sexes, No di fference was observed in the incidence of all-site cancers (age, perio d-adjusted rate ratios by Poisson regression, RR=1.06, 95% confidence interval (CI) 0.79-1.42 for males, RR=0.90, 95% CI 0.65-1.24 for femal es), while stomach cancer incidence seemed to decrease for both sexes (RR=0.70, 95% CI 0.44-1.11 for male, RR=0.58, 95% CI 0.34-1.00 for fem ale) and lung cancer incidence for males only seemed to increase (RR=1 .65, 95% CI 0.83-3.30 for male, RR=1.07, 95% CI 0.28-4.14 for female) in the elevated radon level area. Caution is needed in the interpretat ion of these findings, however, since the individual exposure level wa s not measured and major confounding factors, such as smoking and diet , could not be controlled in this study.