Mortality and cancer incidence among a population previously exposed to environmental cadmium
Objectives: This paper evaluates the associations of previous exposure to environmental cadmium (Cd) and renal function with total mortality and cancer incidence. Methods: The study population comprised 275 residents (aged 40–92 years at baseline) in a Cd-polluted area located on Tsushima Island, Nagasaki, Japan. In the study area, the dietary intake of Cd decreased because the soil of the Cd-polluted rice fields was replaced with new soil between 1980 and 1983. The mortality rate from 1982 to 1997 and cancer incidence from 1985 to 1996 were investigated. Standardized mortality and incidence ratios (SMR and SIR) were calculated by using regional reference rates. The associations of renal function and urinary Cd levels with total mortality and cancer incidence were evaluated with Cox regression models. Results: The SMR for all subjects, and those with a urinary β2-microglobulin (U-β2M) concentration ≥1,000 μg/g creatinine (Cr) and <1,000 μg/g Cr was estimated at 90 [95% confidence interval (CI) 73–109], 138 (95% CI 101–183) and 66 (95% CI 49–87), respectively. After adjustment for age and other potential confounders, in men, serum β2M (S-β2M) (≥2.3 mg/l) and in women, serum Cr (≥1.2 mg/100 ml), relative clearance of β2M (≥1%) and U-β2M (≥1,000 μg/g Cr), were associated with a significantly increased risk of mortality, with hazard ratios exceeding 2.0. After further adjustment for log(U-β2M), the rate ratio of deaths associated with, in men, increased S-β2M was 2.53 (95% CI 0.97–6.65) and, in women, increased serum Cr (S-Cr) concentrations was 2.75 (95% CI 1.24–6.14). Urinary Cd concentrations (≥10 μg/g Cr) were not significantly associated with mortality. The overall SIR of all malignant neoplasms was 71 (95% CI 44–107). Conclusions: These findings suggest that renal tubule dysfunction and a reduced glomerular filtration rate are predictors of mortality among persons previously exposed to environmental Cd. However, the results also suggest that overall mortality rates in Cd-polluted areas are not necessarily increased, because of the low mortality among those with no, or only slight, signs of low-molecular weight proteinuria. Overall cancer incidence may not be increased among residents in Cd-polluted areas.
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