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Since dioxins are fat-soluble, the total amount of dioxins in the body is estimated by multiplying the concentration per lipid by the amount of body fat. The formula commonly used to estimate body fat mass was created nearly 30 years ago. Late-stage elderly patients, such as patients with oil disease, were not included in the development of this formula. In this study, we created a formula to estimate body fat percentage based on the measured value of body fat percentage in the Yusho annual check-ups. Body fat percentage increased in women until their late 60s and in men until their mid-70s, but then tended to decrease. Using this formula for estimating body fat percentage, we verified two studies with half-lives published so far. The first study reported the existence of a group of approximately 10 years reported so far and a group of infinite half-lives with almost no emission. The second study was conducted in the same way as the first study, at a different time, but the number of people in the group of about 10 years decreased and the number of people in the group with infinite half-life increased. When that was done in the study using the new formula for estimating the body fat percentage, the same conclusion was obtained, although there were some differences.

Yusho, the mass food poisoning, occurred in western Japan in 1968. PCBs and dioxin like compounds such as 2,3,4,7,8-PeCDF were detected as causal chemicals for Yusho. Our group have measured blood concentrations of dioxin-like compounds and analyzed their half-lives. In our previous studies, we have found two groups ; one group has 7-10 years of half-lives as reported by other researchers, and the other group has near infinite half-lives. In addition, the number of patients in group showing 7-10 years of half-lives decreased and the number in group with near infinite half-lives increased. However, those changes were not evaluated in individual patient since follow-up period was relatively short to analyze the individual half-live. Therefore, we now intend to evaluate the long-term change of half-life in individual patient. Our preliminary analysis indicates that the half-life of 2,3,4,7,8-PeCDF appears to be prolonged in each patient. Considering the recent low levels of environmental contamination of dioxins and their related compounds, the prolonged half-life of blood concentration of 2,3,4,7,8-PeCDF points its deteriorated excretion.

Yusho, the mass food poisoning, occurred in western Japan in 1968. PCBs and dioxin like compounds such as PCDDs and PCDFs were detected as causal chemicals of Yusho. The Yusho Study Group has conducted annual check-ups for Yusho victims for more than 45 years. Measurement of blood concentration of dioxins became possible on 2002. In this paper, we report the latest findings of the Yusho study regarding the half-lives of dioxins, and discuss the prospects for study of dioxin half-lives in Yuhso victims.

Half-lives of blood levels of 2,3,4,7,8-Pentachlorodibenzofuran (PeCDF) are varied in Yusho patients. The objective was to evaluate a relationship between half-lives of PeCDF levels and types of SNP rs10249788 of aryl hydrocarbon receptor (AHR) gene in 93 Yusho patients. Based on physical symptoms, age, sex, body mass index and other factors, we set up suitable calculation formulas to fit the actual PeCDF levels thorough rates of change in PeCDF.We found that patients with C/T SNP had longer half lives than patients with C/C and T/T SNPs. Patients with T/T SNP are known to express higher amount of AHR mRNAs. However, detailed analysis could not be carried out in T/T group due to a limited number of patients (n=11). Further research is warranted to determine the cause of the longer half-lives in C/T patients.

The relationships among dioxin isomers are not well understood. This study aimed to clarify the relationships among isomers using two methods. First, the relationships between isomers and symptoms were analyzed by analysis of variance. Second, concentrations and half-lives were determined for each isomer in each patient, and correlation coefficients for the concentrations and half-lives among isomers were calculated. Two isomers very similar to 2, 3, 4, 7, 8-pentachlorodibenzofuran (2, 3, 4, 7, 8-PeCDF) were correlated with symptoms of Yusho disease. The correlation coefficients among three isomers similar to 2, 3, 4, 7, 8-PeCDF were very high at 0.98, indicating that there may be a mechanism which maintains constant ratios among these isomers.

Blood levels of dioxins in Yusho patients have been measured for 10 years. The purposes of this study were to determine the half-lives of dioxins on the basis of the data obtained from Yusho patients and to compare the half-lives of the compounds. Linear regression analysis was performed using the binary logarithmic value of each dioxin level as the dependent variable and the year of measurement as the independent variable. The linear coefficient obtained from this linear regression analysis was the reciprocal number of the half-life. The relationship between the blood dioxin levels estimated in 2004 and the reciprocal number of half-life was evaluated. Of the studied dioxins, the concentrations of some compounds were strongly correlated with that of 2,3,4,7,8-PeCDF. For 2 such compounds, the correlation coefficient of the reciprocal numbers of half-life were greater than the correlation coefficient of the logarithmic values of the estimated concentrations. Of these 2 compounds, the concentration of 3,3,4,4,5,5-HxCB was at least 50 times less than that of the 2,3,4,7, 8-PeCDF in rice oil ; however, their current concentrations are equivalent. Patients with high levels of 2, 3, 4, 7, 8-PeCDF also showed high levels of 3, 3, 4, 4, 5, 5-HxCB. Yusho patients may have a disease-specific mechanism to supply 3,3,4,4,5,5-HxCB.

Background : Yusho is an incidence of food poisoning caused by rice bran oil in 1968. Its main causal agent is considered as 2,3,4,7,8-penta-chlorodibenzofuran (PeCDF). The patients have been suffered by the various symptoms, and their blood concentration of PeCDF is still higher than the general population. Objectives : The purpose of this study is to estimate the change rate of PeCDF concentration among the examinees of annual health examination of Yusho patients. Results and conclusions : PeCDF concentration of 118 men and 140 women who received the health examination four times or more from 2001 to 2008 was statistically analyzed. The estimated annual change rate of the PeCDF concentration was low; 1.43% reduction and 1.03% increase were observed, respectively, for men and women who have low PeCDF concentration, and 3.6% and 3.7% reductions, respectively, for men and women who have high concentration of PeCDF. The reduction rate was associated with age and smoking habit in men, and drinking habit in women.