Longitudinal studies on the health effects of exposure to environmental cadmium

Renal damage induced by cadmium (Cd) results in a proximal renal tubular dysfunction, characterized by low-molecular weight (LMW) proteinuria, renal glucosuria, generalized aminoaciduria and decreased renal tubular reabsorption of uric acid and phosphate. Since LMW proteinuria is thought to be one of the earliest adverse health effects caused by Cd, the prevention of the progress of LMW proteinuria is important to avoid further deteriorations in the health condition. Follow-up studies on residents in Cd-polluted areas and Cd-exposed workers have indicated that Cd-induced LMW proteinuria is generally irreversible and progressive even after the cessation or reduction of exposure. The intensity of exposure and the body burden of Cd before the reduction of exposure may influence the prognosis of Cd-induced LMW proteinuria. Several studies have reported a gradual decline in the glomerular filtration rate even after the reduction of Cd exposure. Cohort studies performed in Cd-polluted areas of Japan showed that renal tubular dysfunction and a decreased glomerular filtration rate were strongly associated with increased risk of mortality. However, the results also suggested that overall mortality rates in Cd-polluted areas were not necessarily increased, because of the low mortality among those with urinary beta 2-microglobulin concentrations < 1,000 micrograms/g creatinine. At present, incidence data are too limited to draw a conclusion regarding the cancer risk among residents in Cd-polluted areas.