A Risk Comparison between Lifestyle, Socioeconomic Status, and Radiation: A Cohort Study of Cancer Mortality among Japanese Nuclear Workers (J-EPISODE).

ABSTRACT: The health effects of low-dose radiation exposure have been a source of controversy. One possible reason is that epidemiological studies that compare radiation risk with other factors, such as lifestyle or socioeconomic status, have been limited. The aim of this study is to conduct a comparison of the cancer risk of mortality between radiation, lifestyle habits (such as smoking), and socioeconomic status (such as years of education) among Japanese nuclear workers. We assembled a cohort of 41,742 male nuclear workers in Japan who answered a lifestyle questionnaire survey conducted during 2003-2004. To exclude systematic errors caused by missing values, we used multiple imputation and Poisson regression to estimate relative risks and confidence intervals for lifestyle habits, socioeconomic status, and radiation. The total person-y from 2005 to 2010 were 215,000. The mean age and cumulative dose were 54.9 y and 24.8 mSv (10-y lagged dose), respectively. Significantly high relative risks were determined for smoking, alcohol consumption, frequency of medical examination, breakfast intake, sleep, and body mass index. Further, significantly high relative risks of radiation were shown for lung cancer and smoking-related cancers. Since the simultaneous inclusion of radiation and non-radiation variables in the model for relative risk (RR) calculation means that the calculated radiation RR is the result of adjustment by other variables, the risk of cancer from low-dose radiation, if any, is less than smoking and probably less than other lifestyle factors.

Organ Dose Reconstruction Applicable for a Japanese Nuclear Worker Cohort: J-EPISODE.

ABSTRACT: An evaluation of cancer risk based on organ-absorbed dose is underway for the Japanese Epidemiological Study on Low-Dose Radiation Effects (J-EPISODE), which has analyzed health effects in association with radiation exposure evaluated with the personal dose equivalent Hp(10). Although the concept of effective dose and its operational definition of Hp(10) are widely used for radiological protection purposes, effective dose is not recommended for epidemiological evaluation. Organ-absorbed dose was instead adopted for the IARC 15-Country Collaborative study (15-Country study), the International Nuclear Workers Study (INWORKS), the Mayak worker study, and the Life Span Study (LSS) of atomic bomb survivors. The reconstruction method in J-EPISODE followed in principle the approach adopted in the 15-Country Study. As part of the approach of J-EPISODE, a conversion factor from photon dosimeter reading to air kerma was developed using dosimeter response data, which were measured by the experiment using an anthropomorphic phantom, and it was confirmed that the 15-Country study's assumption of photon energy and geometry distribution in a work environment applied to Japanese nuclear workers. This article focuses on a method for reconstructing the conversion factor from photon dosimeter reading to organ-absorbed photon dose for a Japanese nuclear worker cohort. The model for estimating the conversion factor was defined under the assumption of a lognormal distribution from three concerned bias factors: (1) a dosimeter reading per air kerma, i.e., dosimeter response; (2) an organ-absorbed dose per air kerma; and (3) a factor relating to the differences in dose concepts and calibration practices between the roentgen dosimeter era and the present. Dosimeter response data were cited from the companion paper. Data on organ-absorbed photon dose per air kerma were estimated using a voxel phantom with the average Japanese adult male height and weight. The bias factor for the recorded dose in the roentgen era was defined, considering the backscatter radiation from the human body. The estimated values of organ-absorbed photon dose per air kerma were almost the same as those in ICRP Publication 116, revealing that the effect of differences in body size was almost negligible. The conversion factors from dosimeter reading to organ-absorbed dose were estimated by period (the roentgen era or from then), nuclear facility type (nuclear power plant or other), dosimeter type, and tissue or organ. The estimated conversion factors ranged from 0.7 to 0.9 (Gy Sv-1). The estimated cumulative organ-absorbed photon dose for the participants of J-EPISODE demonstrated that organ-absorbed dose values were approximately 0.8 times the recorded doses if neglecting dose-unit differences. J-EPISODE reconstructed an organ-absorbed dose conversion factor and will evaluate the risk of cancer mortality and morbidity using the organ-absorbed dose in the future.

ESTIMATION OF PHOTON ENERGY AND DIRECTION DISTRIBUTIONS AT JAPANESE NUCLEAR POWER PLANTS BASED ON LITERATURE SURVEY FOR J-EPISODE STUDY.

In order to reconstruct organ-absorbed dose from recorded dose for risk estimation in nuclear worker cohort, the preceding study of the International Agency for Research on Cancer (IARC) 15-Country Collaborative Study estimated the organ dose conversion factor from the recorded dose of Hp(10) under the assumption that on average, in the nuclear power plants (NPPs), 10% of the dose received by workers was due to photon energies ranging from 100 to 300 keV and 90% from photon energies ranging from 300 to 3000 keV, with the average geometry being 50% in the antero-posterior geometry and 50% in the isotropic geometry. Similar examination was conducted at the Japanese Epidemiological Study on Low-Dose Radiation Effects (J-EPISODE). Literature survey disclosed that Japanese electric power companies had jointly conducted the research on energy distribution and incidence direction distribution of gamma rays in working environments during periodical inspection and maintenance as well as during operation in the 1980s. The analysis of the survey results on photon energy and geometry distribution of Japanese NPPs demonstrated appropriateness in applying the IARC study assumption for nuclear workers in Japan and reconstructing organ-absorbed dose in the J-EPISODE. These results in Japan also provide strong evidence to support the robustness and generality of the IARC study assumption, which was estimated based on the judgment of experts at nuclear facilities around the world.

CONVERSION FACTOR FROM DOSEMETER READING TO AIR KERMA FOR NUCLEAR WORKER USING ANTHROPOMORPHIC PHANTOM FOR FURTHER CONVERSION FROM AIR KERMA TO ORGAN-ABSORBED DOSE.

Estimation of cancer risk based on the organ-absorbed dose is underway for the Japanese Epidemiological Study on Low-Dose Radiation Effects (J-EPISODE). The reconstruction method for the organ-absorbed dose follows the approach adopted in the IARC 15-Country Collaborative Study, which examined the dosemeter response to photon exposure for the old film badge (FB) type, a multi-element FB and a thermoluminescence dosemeter. Until 2000, the dosemeters used in Japan were almost the same in the IARC study, so IARC study data could be used as they were. However, since 2000, the type of dosemeter has been replaced with active personal dosemeters (hereafter called electronic personal dosemeters), radio-photoluminescent glass dosemeters (Glass badge) and optically stimulated luminescence dosemeters (Luminess badge). Hence, it was necessary to collect these data again. A dosemeter response experiment was conducted using a device that irradiated an anthropomorphic phantom in the Japan Atomic Energy Agency calibration laboratories. The aim of the paper is to provide a conversion factor from reading in terms of Hp(10) to air kerma for realistic conditions for further conversion from air kerma to organ-absorbed dose. The obtained dosemeter responses for the dosemeter types currently used in Japan were consistent with those in the IARC study. These data will be utilized for J-EPISODE in reconstructing the organ-absorbed dose.

Improvement of cognitive functions by oral intake of Hericium erinaceus.

Hericium erinaceus has been recognized as medical mushroom since ancient time, but its scientific evidence for human health has been still uncertain. In this study, we tested a randomized, double-blind, placebo-controlled parallel-group comparative study to evaluate the improvement of the cognitive functions by taking supplements containing fruiting body of H. erinaceus for 12 weeks. We performed three kinds of tests: Mini Mental State Examination (MMSE), Benton visual retention test, and Standard verbal paired-associate learning test (S-PA). MMSE alone showed that oral intake of H. erinaceus significantly improved cognitive functions and prevented from the deterioration. We speculate that various chemical compounds, including hericenones, in the mushroom have multiple effects to the brain neural networks and improve cognitive functions. Oral intake of H.erinaceus is safe and convenient method for dementia prevention so far.

Income-Related Inequalities in Access to Dental Care Services in Japan.

Background: This study aimed to evaluate whether income-related inequalities in access to dental care services exist in Japan. Methods: The subjects included beneficiaries of the National Health Insurance (NHI) in Chiba City, Japan, who had been enrolled from 1 April 2014 to 31 March 2015. The presence or absence of dental visits and number of days spent on dental care services during the year were calculated using insurance claims submitted. Equivalent household income was calculated using individual income data from 1 January to 31 December 2013, declared for taxation. Results: Of the 216,211 enrolled subjects, 50.3% had dental care during the year. Among those with dental visits, the average number of days (standard deviation) spent on dental care services per year was 7.7 (7.1). Low income was associated with a decreased rate of dental care utilization regardless of age and sex. However, there was a significant inverse linear association between the number of days spent on dental care services and income levels for both sexes. Conclusions: There were income-related inequalities in access to dental care services, regardless of the age group or sex, within the Japanese universal health insurance system.