Objectives: Minamata disease (MD), first discovered in 1956, is a neurological disorder caused by mercury poisoning due to daily intake of fish and shellfish that have been contaminated by methylmercury discharged from chemical factories. However, reports of ill health increased sharply following the 2004 Supreme Court ruling instructing the Japanese government to pay damages to MD patients. We examined the distribution of disability in activities of daily living (ADL), and the association between MD status in terms of compensation system and ADL disability among the general population of previously methylmercury-polluted areas.
Methods: Data were collected by two-stage stratified sampling of residents 40-79 years old in 172 postal-code areas on the Shiranui Sea coast, the endemic area of MD. Questionnaires were distributed to eligible subjects (n = 2100) and collected at a later visit or by mail. Information on demographic factors, basic ADL (BADL), and instrumental ADL (IADL) was obtained using questionnaires. We performed logistic regression analysis to assess the relationship between MD status in terms of compensation system and ADL disability.
Results: We classified the 1422 residents who completed the questionnaire in accordance with their MD status in terms of compensation system: Early (those who received MD compensation before the Supreme Court decision), Recent (those who applied for compensation after the Supreme Court decision), Not Yet (those who have not yet applied for compensation, but have health-related anxieties about MD effects), and Normal (those who have not applied for compensation, and do not have health-related anxieties about MD effects). Adjusting for confounding factors, MD status was significantly associated with the disability grades of BADL and IADL with an increasing trend in the order of Normal, Not Yet, Recent, and Early. The odds ratios (95% CI) based on Normal were 2.08 (1.08-4.01), 3.87 (2.14-7.01), and 4.50 (2.66-7.61) for BADL and 2.41 (1.62-3.61), 3.20 (2.12-4.85) and 3.68 (2.52-5.38) in Not Yet, Recent, and Early for IADL, respectively.
Conclusion: Early, Recent, and Not Yet had lower ADL grades than Normal. Moreover, the population with a low ADL grade and health-related anxieties had increased throughout the previously methylmercury-polluted areas. The issue of ill health among populations living in previously methylmercury-polluted areas should be addressed in the wider context of public and community health.