Causes of death in patients with Itai-itai disease suffering from severe chronic cadmium poisoning: a nested case-control analysis of a follow-up study in Japan

Objective To clarify the causes of deaths among patients with Itai-itai disease and severe cadmium (Cd) poisoning. Design Nested case-control analysis of a population-based cohort study. Setting Database of patients with Itai-itai disease and residents of Cd-polluted areas, maintained by the Ministry of Environment, Japan. Participants Subjects included 142 women with Itai-itai disease, 111 women with Cd-induced renal tubular dysfunction and 253 controls matched for sex, age and occupation. All subjects participated in a health impact survey between 1979 and 1984 and were followed until 30 November 2005. Main outcomes and measures Adjusted HRs with 95% CIs for cause of death in women with Itai-itai disease and screened female cases with tubular dysfunction were compared with matched pair controls, using Cox's proportional hazard model. Vital statistics data were used to determine cause of death. Direct causes of death from autopsy records were used in 29 patients who died from Cd poisoning. Results The most common cause of death among patients with Itai-itai disease was pneumonia, with a significantly increased adjusted HR of 4.54 (95% CI 2.65 to 7.76). Renal diseases were the most common cause of death in renal tubular dysfunction cases, with an increased HR of 12.0 (95% CI 3.92 to 36.8). The adjusted HR for renal diseases was also significantly increased in patients with Itai-itai disease (19.49 (95% CI 6.43 to 59.09)), with a greater impact on mortality of patients with Itai-itai disease than screened cases. The HR for gastrointestinal (GI) diseases was significantly increased (13.79 (95% CI 3.87 to 49.10)) in patients, especially in the first 10 years (37.1 (4.81 to 286.0)). Conclusions Among patients with Itai-itai disease, pneumonia and GI diseases contributed to increased mortality risk. Renal disease is also a significant mortality risk in patients with Itai-itai disease and women with renal tubular dysfunction.