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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.The purpose of this study is to estimate the change rate of PeCDF concentration among the examinees of annual health examination of Yusho patients.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.

Polychlorinated biphenyls (PCBs) are known to cause the release of superoxide during the metabolic process. Therefore, it is suggested that the Yusho patients are exposed to oxidative stress caused by high concentrations of PCBs are still recorded in their serum. Recently, diacetylspermine (DiAcSpm) has been proposed as tumor markers or barometer of oxidative stresses. In order to estimate the ability of urinary DiAcSpm as a potential marker of dioxin or PCB exposure, we measured urinary DiAcSpm in Yusho patients and assessed the association of DiAcSpm with serum PCBs and dioxins levels. The statistical analysis did not indicat that urinary DiAcSpm is useful for detection of exposure to PCBs or dioxins, although a few Yusho patients showed high level of DiAcSpm.

A nation-wide questionnaire survey on the past history of diseases and symptoms was conducted in 2005. The questionnaire was administered by mail to the 1258 registered Yusho patients, inguiring about the past incidence of 15 regions of malignant neoplasm, 42 diseases, and 5 symptoms. Out of the 717 patients responded to the questionnaire, 34 patients born after the Yusho outbreak were excluded, leaving 683 patients as the study subjects. Their mean age (SD) was 62.7 (14.0) years, ranging from 39 to 97 years old. Seven percent of the patients acknowledged the past history of malignant neoplasm in one or more regions. More than 40% admitted the past history of dental diseases, pain of joints, numbness of limbs, fatigue, headache, cough and sputum. Osteoporosis and myoma of the uterus, respectively, were reported by 22.8% and 15.6% of women. 14.2% of men reported prostatic hypertrophy. Logistic regression analysis was performed to estimate the association of the past history of diseases with the blood lipid level of 2,3,4,7,8-pentachlorodibenzofuran adjusting for sex and age. In the whole study subjects, 306 patients were measured the PeCDF level once or more in the years from 2001 to 2005. We found statistically significant elevation of the proportion of the patients with the past history of prostatic hypertrophy with increasing blood lipid level of 2,3,4,7,8-PeCDF (P = 0.03). The marginally significant positive association between the proportion of the patients with the past history of hypertension and 2,3,4,7,8-PeCDF was observed (P = 0.06).