[Epidemiology of Minamata Disease--Focus on the Clinical Features Related to the 1977 Diagnostic Criteria].

Large-scale food poisoning caused by methylmercury was identified in Minamata, Japan, in the 1950s (Minamata Disease). Although the diagnostic criteria for the disease was controversial and difficult during that time, we, the Kumamoto University Study Group, carried out a large-scale study to assess the clinical features in 1972-1973. The author tried to reassess the results of that study to appraise the diagnostic criteria established in 1977 on the basis of those results. A substantial number of residents in the exposed area exhibited neurologic signs, especially paresthesia of only the extremities, namely, the male residents of Minamata City showed a positive predictive value of 0.73 and a negative predictive value of 0.23. The relative risks of paresthesia only were 2.6 (2.0-3.3) and 1.2 (0.9-1.5), in Minamata and Goshonoura related to Ariake (control), respectively. At least until 1977, the diagnostic criteria remained valid, although it was inadequate. Nevertheless, presently, a follow-up study of the certified patients may lead to the development of efficient new diagnostic criteria.

Correlation between bone mineral density and body composition in Japanese females aged 18-40 years with low forearm bone mineral density.

OBJECTIVES: To clarify the relationship between bone mineral density (BMD) and body composition in Japanese women aged 18-40 years with low forearm BMD. METHODS: The subjects were Japanese 199 women who had been selected for inclusion in the study based on a low forearm BMD determined at the Annual Women's Health Examination. The subjects' mean (+/- standard deviation) age, body height, body weight, and body mass index (BMI) were 33.5 (+/-4.3) years, 158.1 (+/-5.1) cm, 49.6 (+/-5.7) kg, and 19.8 (+/-2.1), respectively. The BMD of the lumbar spine, total body, and left arm were measured using dual-energy X-ray absorptiometry (DXA). Fat mass (FM), bone-free lean tissue mass (LTM), and body fat percentage (BF%) were measured simultaneously with DXA. RESULTS: In the structural equation model, the standardized regression weights for the path from BMI to BMD of all sites were 0.273-0.434. Conversely, the BF% to BMD of the total body and left arm were -0.192 and -0.296, respectively. In multiple regression analysis, the FM index (FMI) was significantly associated with the BMD of the lumbar spine as a weight-bearing site. The LTM index (LTMI) was significantly associated with the BMD of the total body and left arm as a non-weight-bearing site. CONCLUSIONS: Young females with low forearm BMD had low body weight and BMI. Thinness was shown to be a risk factor for low BMD, in accordance with results reported elsewhere. A gain in body weight may have the effect of increasing BMD, but our results suggest that to increase BMD, the gain in body weight must include increases in LTM, and not FM alone.

Long-term follow-up study of health status in population living in methylmercury-polluted area.

At present, it is important to follow-up on the health condition of inhabitants living in a methylmercury-polluted area surrounding Minamata City, paying attention to subclinical disorders not only of the central nervous system, which have been concentrically studied for more than 40 years, but also to other health issues as well. We have performed annual follow-up multiple health examinations on about 1,500 persons of ages more than 40 years old in Tsunagi Town near Minamata City each summer from 1984 to 2004. Case-control studies were designed to estimate the role of risk factors for various health issues using geographical differences to compare the verified patients. The results of the study are summarized as follows: (1) There were no significant differences in the prevalence of diseases associated with Minamata disease (MD) (e.g., liver diseases, renal diseases). (2) Subjective complaints, which were related not only to neurological but also to general complaints were consistently much more common in the polluted area than in the control area. (3) Five percent of the inhabitants who were not certified as MD patients had a high predicting index of MD. They could be affected by methylmercury poisoning. It is important to make a differential diagnosis. (4) No significant differences with respect to ADL by residential area were observed. However, MD patients who stayed in their homes showed some impairments of instrumental ADL. (5) It is important to take into consideration mental distress not only from the physical effects but also from the secondary social damage experienced through MD in these area.

[Factors relating to the conditions and characteristics of mental health among the inhabitants in a methylmercury polluted area].

OBJECTIVES: Little attention has been paid to mental health of inhabitants of methylmercury-polluted areas. The objective of this study was to examine the factors relating to the conditions and characteristics of mental health of inhabitants residing in a methylmercury-polluted area. METHODS: The eligible subjects of the study were inhabitants over the age of 40 years (n=301) living in two fishing village districts that were polluted by high concentrations of methylmercury. The study was conducted in two phases. In the first phase, a structured questionnaire was used to gather information on the current health condition and experience with Minamata disease of each subject through interviews. In the second phase, the General Health Questionnaire (GHQ)-30 was distributed to measure the psychological distress of the respondents. RESULTS: There were 133 (44.2%) study subjects. Factor analysis of the data collected using the GHQ was carried out and five factors that accounted for 57.9% of the total variance were selected. The first factor was labeled "depression and anxiety". Depression and anxiety were significantly associated with self-rated health status, the number of subjective symptoms, monthly outpatient visits and the receipt of compensation. Covariance structure analysis using the Amos 4.0 program demonstrated that depression and anxiety were significantly associated with the subjects' health condition, which in turn was influenced by experience with Minamata disease. CONCLUSION: Depression and anxiety of the inhabitants may be directly caused by the health condition. Further investigations with more precise and detailed measurements are needed to corroborate the causal relationship.

Hand arm vibration syndrome among quarry workers in Vietnam.

Few studies have focused on the health effects of vibrating tools on workers in the tropical area. Work conditions and health effects related to rock drill operation were studied in 102 quarry workers, including 73 rock drill operators in Vietnam. We aimed to clarify (1) risk of vibration exposure, (2) occurrence of vibration-induced white finger (VWF), and (3) characteristics of hand-arm vibration syndrome (HAVS). Total weighted r.m.s. acceleration of the Chinese -or Russian-made rock drills, was 45-55 m/s(2). According to work observation studies, daily exposure time to vibration was 160-210 min. ISO5349 predicted that this exposure level would be associated with a high risk of HAVS in workers. We found no clear evidence of VWF. There may be several reasons why no worker exhibited VWF: (1) warmer work conditions, (2) younger and less experienced workers, (3) seasonal changes in work operations, and (4) healthy worker effect. On the other hand, 5-10% of rock drill operators might be suffering from moderate HAVS which was sensori-neural type dominant. There may be some characteristic features of HAVS among quarry workers in the tropical area.

Correlation between forearm bone mineral density and body composition in Japanese females aged 18-40 years.

OBJECTIVE: The purpose of this study was to clarify the relationship between forearm bone mineral density (BMD), body mass index (BMI), and body composition focusing on body fat percentage (BF%) in Japanese females 18 to 40 years old. METHODS: Subjects were 2,280 females 18-40 years old. Anthropometric measurements were taken, and a medical history was obtained by questionnaire, including age at the time of the study and age at menarche. BF% was measured by bioelectrical impedance analysis. Forearm BMD was measured using dual-energy X-ray absorptiometry (DXA). The correlations of BMD with BMI and BF% were analyzed using a structural equation model. RESULTS: The standardized regression coefficients for the path from BMI to BMD and the path from BF% to BMD were 0.538 and -0.184 respectively. The squared multiple correlation of BMD was 0.146. In addition, the standardized regression coefficient for the path from BMI to BF% was 0.896. CONCLUSION: The results showed a positive correlation between BMD and BMI and an inverse correlation between BMD and BF%. At the same time, it was noted that BF% increased with BMI. This indicated that BMD is dependant on BF% in subjects who have a similar BMI. Therefore, this study concluded that it is necessary to take body composition measurements into account when examining the relationship between BMI and BMD, especially in young females.

Exploring the influence of depressive symptoms on physical disability: a cohort study of elderly in Beijing, China.

OBJECTIVES: This study examined the influence of depressive symptoms on the prevalence of physical disability in a cohort study of Beijing elderly (1992--2000) and analyses the role of some confounding variables in this relationship. METHODS: A cohort of 1828 elderly aged 55 and older who were initially free of any physical disability was followed up for 8 years. Baseline depression was assessed by the Center for Epidemiological Studies Depression Scale. Disability on activities of daily living (BADL and IADL) was measured in 1994, 1997, and 2000 respectively. RESULTS: The cumulative percentages of persons who developed BADL disability and IADL disability during each follow-up interview was significantly greater among depressed than non-depressed individuals. Compare with the 1525 non-depressed individuals, the 303 depressed individuals had a relative risk (95% confidence interval) of 2.52 (2.02, 4.82) for BADL disability and 4.98 (2.46, 10.09) for IADL disability, respectively. Although adjustment for confounding factors reduced the risk to 2.20 (1.33, 3.62) and 4.29 (2.08, 8.86), the detrimental effect of depression on disability remained significant. The items of IADL which connected physical activity had higher impairment among depressed individuals. CONCLUSIONS: Depression in elderly persons may increase the risk for prevalent disability. It is very important for elders to prevent and reduce depression for improving the quality of their life and physical function.

Social factors associated with psychological distress among inhabitants in a methyl-mercury polluted area in rural Japan.

Little attention has been paid to the mental health of inhabitants of methylmercury-polluted areas in Japan. This study examined the relationship between one's experience with Minamata disease (MD) (such as compensation issues) and psychological distress. The subjects were 133 (44.2%) of the 301 inhabitants over the age of 40 years living in two fishing village districts along the coast of the Yatsushiro Sea which had been contaminated with methylmercury. Data on the inhabitants' experience with MD, social network factor, health condition and mental health were obtained using questionnaires including the General Health Questionnaire (GHQ)-30. The proportional odds model was used to estimate the adjusted odds ratios of factors associated with a higher GHQ score after adjustment for age, sex and village. MD status based on MD compensation, level of participation in MD patients' groups, and presence of certified MD patients in the family were significantly associated with psychological distress. Although these associations decreased after further adjustments were made taking health condition into consideration, MD status, participation in several sit-ins and the presence of certified MD patients in the family maintained marginally positive association with psychological distress. Further investigations with more precise and detailed measurements are needed to corroborate the relationship between inhabitants' experience with MD and mental health.

Relationship between health status and psychological distress among the inhabitants in a methylmercury-polluted area in Japan.

This study examined the relationship between health parameters and psychological distress among inhabitants of methylmercury-polluted areas in Japan. The subjects were 133 inhabitants over the age of 40 yr living in two methylmercury-polluted villages. Information on demographic factors, health status, and mental health was obtained using questionnaires, including the General Health Questionnaire (GHQ). The proportional odds model was used to estimate the adjusted odds ratios of factors associated with a higher GHQ score after adjustment for age, gender, and district. Very poor self-rated health status, a high number (5+) of subjective symptoms, having monthly outpatient visits and medical house calls, and receiving compensation for methylmercury poisoning were significantly associated with psychological distress. Poor physical condition may lead to the development of psychological distress.

[Health and socio-economic condition of certified Minamata disease patients, 1999].

OBJECTIVES: To clarify the needs and to consider establishing a social support system for patients with Minamata disease (MD), or methylmercury poisoning, by investigating their health and socioeconomic conditions. METHODS: The total number of people certified as having MD in May 1999 by the Kumamoto and Kagoshima Prefecture Government Committees on MD was 2265. We sent two questionnaires to 917 individuals who were surviving at that time, which corresponded to 40.5% of the total number of MD patients. The first survey sought information on the individual's health-seeking behavior, and the second survey was about their socio-economic conditions and requirements for welfare and medical care in the future. RESULTS: The average age among male patients was 68.0 +/- 13.2 yrs (n = 477) and that among female patients was 71.2 +/- 13.0 yrs (n = 440). The response rates were 45.7% (n = 416) for the first questionnaire and 38.6% (n = 354) for the second questionnaire. Among the MD patients, 71.7% judged their health condition to be 'bad' or 'very bad', and 97.4% received medical treatments that included acupuncture or moxacautery and massage. Regarding the activity of daily living (ADL), which includes 'communicating', 'walking', 'eating', 'use of toilet', 'dressing' and 'taking a bath', the rates of 'independent' were relatively low among those under 49 yrs and those over 75 yrs compared with the other age groups. Many individuals emphasized that they had anxiety about their health and health care in the future. CONCLUSION: We concluded that the quality of life (QOL) of MD patients was low. It is important to consider developing a social support system for MD patients.

Relationship between questionnaire survey results of vibration complaints of wheelchair users and vibration transmissibility of manual wheelchair.

OBJECTIVE: Clarify the relation between the complaints of wheelchair users and the vibration characteristics of the wheelchair, to improve wheelchair comfort and design. METHODS: The question naires were distributed to 33 wheelchair users directly by the experimenter in order to identify the causes of complaints from wheelchair vibrations that they experienced. The vibration transmissibility of wheelchairs of ten subjects was measured to clarify the causes of complaints of wheelchair vibration according to the ISO 10326-1 standard in the laboratory using a broadband random vibration spectrum with a frequency-weighted vibration magnitude of 0.1 ms(-2) r.m.s. over the frequency range from 0.2 to 100 Hz. Each vibration exposure lasted 60 seconds. RESULTS: The following findings were clear from the questionnaire results; (i) the vibration rom the wheelchair affected psychological comfort; (ii) the effects of different riding surfaces were important engineering issues affecting wheelchair ride comfort; (iii) the wheelchair users felt the vibration during wheelchair usage at locations on the neck, lower back and buttocks; (iv) vertical vibration was the most noticeable vibration from the wheelchair to each participant's body. The following findings were clear from the results of the transmissibility measurement of the wheelchair; (i) the resonance frequency-ranges of the transmissibility of the wheelchair showed significant differences between the subjects; (ii) intra-subject variability from three repeated transmissibility measurements was small; (iii) the first resonant frequency occurred approximately 5 to 7 Hz and the second resonant frequency occurred at around 8 Hz and the third resonant frequency occurred approximately 13 to 15 Hz; (iv) the magnitude of the peak transmissibility varied from 1.3 to 2.6. CONCLUSION: From the comparison of the results of questionnaires and the transmissibility measurement of the wheelchair, the resonance frequency-ranges of the maximum vibration transmissibility of the manual wheelchairs were consistent with the frequency-ranges of the body parts of the causes of the complaints of wheelchair users. In addition, from these experimental results, it was suggested that the main point for improving a wheelchair user's comfort was to reduce the wheelchair seat vibration transmissibility at around 8 Hz and also to design wheelchair stiffness and damping characteristics to minimize vibration transmission at specific frequencies at body locations that caused the discomfort reported by wheelchair users.

Serial study on the association between body mass index and hypertension in rural Japanese.

The objective of this study was to examine the association between body mass index (BMI) and blood pressure. Two sets of cross-sectional data were obtained from annual health examinations for adults aged 40 years and over (n=1,327 in 1993; n=1,302 in 2000) in Tsunagi area of Kumamoto Prefecture, Japan. BMI was associated with mean blood pressure and with prevalence of hypertension both in 1993 and 2000. The association was independent of age, smoking status and alcohol consumption. A significant increase in risk of hypertension was found in most categories of BMI 25.0 and above, and a greater than three fold increase in those with BMI of 27 and above compared with those with BMI of 18.5-22.9. Although mean blood pressure and prevalence of hypertension sharply decreased in 2000 compared with that in 1993, BMI was positively and independently associated with increased blood pressure.

Occupational dermatoses among fibreglass-reinforced plastics factory workers.

Fibreglass-reinforced plastics (FRP) factory workers are at high risk of developing occupational dermatoses because of their exposure to many chemicals used in the manufacture of plastics as well as to glass fibre or dust. Patch tests were carried out on 29 workers involved in FRP manufacturing processes where unsaturated polyester (UP) resin was used, to investigate the causes of their skin problems. Of the 22 workers who reported experiencing skin problems, 16 showed positive results to at least 1 chemical, including 6 cases of multiple sensitivity. 2 showed positive reactions to UP base resin, 6 to cobalt chloride, 5 to benzoyl peroxide (BPO), 4 to methyl ethyl ketone peroxide (MEKPO), 2 to para-tertiary butyl catechol (PTBC), 1 to styrene and 1 to formaldehyde. After taking into account their exposures and reported causes by questionnaires and their patch test results, 7 cases were diagnosed as allergic contact dermatitis (ACD) due to chemicals, 3 as irritant contact dermatitis (ICD) due to chemicals, and 3 as dermatitis due to mechanical irritation (MI) from glass fibre or dust, as well as 9 as ACD and/or MI. 18 of the total of 29 subjects (62.1%), including 2 workers without a history of skin problems, were sensitized to at least 1 chemical. Cobalt, peroxides, PTBC and UP base resin were the common causes of ACD.

Demographic determinants for change in activities of daily living: a cohort study of the elderly people in Beijing.

To describe changes in activities of daily living (ADL) of community-dwelling Beijing elderly people, observed for 8 years, and to identify the demographic characteristics that predict the functional change. Four sets of interview data from 1992 to 2000 were used to evaluate changes among Beijing elderly aged 55 years and over. Results revealed that prevalence of disability increased from 3.9% to 7.1% during the 8 years of follow-up with the average increasing rate of disability was 0.41% per year. Meanwhile an increasing likelihood of recovery from disability is observed with age and time. Women, aged 75 or more, experienced higher disability than men though it was in the opposite for younger ages. In addition, certain demographic subgroups (such as women, unmarried, illiterate and living in non urban area) appeared to be at higher risk for ADL impaired. The patterns of ADL change is in both the direction of improvement and declination. Demographic variables emerged as a significant predictor in estimating functional outcomes. Furthermore, it is recommended that the demarcation factor for the evaluation of ADL should be 75 years of age.

Skin problems among fiber-glass reinforced plastics factory workers in Japan.

Two surveys, one in winter the other in summer time, examined the skin problems of the entire manual workers (N=148) from 11 small-to-medium sized fiber-glass reinforced plastics (FRP) factories located in Kyushu, Japan. The workers were exposed to unsaturated polyester resin, including styrene and auxiliary agents such as cobalt naphthenate, hardeners such as methyl ethyl ketone peroxides, glass fiber and dust including shortened glass fiber and plastic particles. Eighty-seven workers (58.8%) reported having skin problems (mainly itching or dermatitis) since they started to work in FRP manufacturing and 25 workers had consulted a physician because of their skin problems; one worker was forced to take sick leave because of his severe dermatitis. History of allergic diseases and shorter occupational period (duration of employment) in a FRP factory were associated with greater probability of having a history of work-related skin symptoms. Workers in factories where dust-generating and lamination sites were located in different buildings were significantly less likely to have a history of skin problems than those in factories where the two sites were located in the same building. Of the 67 workers examined in both seasons closed to double the prevalence of dermatitis was found in summer (23.3%) than winter (13.4%).

Logistic model analysis of neurological findings in Minamata disease and the predicting index.

OBJECTIVE: To establish a statistical diagnostic method to identify patients with Minamata disease (MD) considering factors of aging and sex, we analyzed the neurological findings in MD patients, inhabitants in a methylmercury polluted (MP) area, and inhabitants in a non-MP area. MATERIALS AND METHODS: We compared the neurological findings in MD patients and inhabitants aged more than 40 years in the non-MP area. Based on the different frequencies of the neurological signs in the two groups, we devised the following formula to calculate the predicting index for MD: predicting index = 1/(1+e(-x)) x 100 (The value of x was calculated using the regression coefficients of each neurological finding obtained from logistic analysis. The index 100 indicated MD, and 0, non-MD). RESULTS: Using this method, we found that 100% of male and 98% of female patients with MD (95 cases) gave predicting indices higher than 95. Five percent of the aged inhabitants in the MP area (598 inhabitants) and 0.2% of those in the non-MP area (558 inhabitants) gave predicting indices of 50 or higher. CONCLUSION: Our statistical diagnostic method for MD was useful in distinguishing MD patients from healthy elders based on their neurological findings.

Autonomic nervous functions in fetal type Minamata disease patients: assessment of heart rate variability.

In order to assess the cardiovascular autonomic nervous functions in patients with fetal type Minamata disease (FMD), we investigated blood pressure (BP), and conducted time and frequency domain analysis of heart rate variability (HRV). Subjects were 9 patients in Meisuien recognized as FMD, and 13 healthy age matched control subjects. HRV and BP were assessed after subjects rested in a supine position for 10 minutes. Electrocardiographic (ECG) data were collected for 3 minutes during natural breathing. Time domain analysis (the average of R-R intervals [Mean RR], standard deviation of R-R intervals [SD RR], coefficient of variation [CV]), and frequency domain analysis by fast Fourier transformation (FFT) (power of low frequency [LF] and high frequency [HF] component, expressed in normalized units[nu]) were then conducted. In the time domain analysis, the mean RR of the FMD group was significantly lower than that of the control group. Neither SD RR nor CV showed significant differences between the two groups, but both tended to be lower in the FMD group. In the frequency domain analysis, the HF component of the FMD group was significantly lower than that of the control group. Pulse pressure (PP) was significantly lower in the FMD subjects. These findings suggest that parasympathetic nervous dysfunction might exist in FMD patients, who were exposed to high doses of methylmercury (MeHg) during the prenatal period. Decrease of PP might be due to degenerative changes of blood vessels driven by exposure to high doses of MeHg.