Validity of cadmium concentration in rice as the "dose" of the dose-response relationship between cadmium intake and renal dysfunction

It is well known that cadmium (Cd) causes renal dysfunction such as increas e of beta (2)-microglobulin excretion into urine. Although Cd in rice seems to be one of the largest sources of total Cd intake in Japan, there are ve ry few studies that have epidemiologically clarified the relationship betwe en Cd concentration in rice (Cd-R) and renal dysfunction, because such stud ies are basically ecological studies, in which confounding factors are diff icult to take into consideration. To derive safety levels for foodstuff fro m Cd-R, it is essential to evaluate the effect of confounding factors. Thus , we investigated the dose-response relationship between renal dysfunction and not only Cd-R but also confounding factors, and we tried to determine w hether Cd-R is an adequate indicator of "dose" in the dose-response relatio nship between Cd intake and renal dysfunction. In 1971, Cd-R data were obta ined from rice samples collected by the Environment Agency, Government of J apan in the Fuchu area of Toyama Prefecture, which is known as a place wher e many itai-itai disease patients were found, and medical data were collect ed during 1979-1984 by Toyama Prefecture. First, the dose-response relation ship between Cd-R and renal dysfunction was analyzed using the data from th e Fuchu area. Second, to investigate the effect of confounding factors, ana lysis using the data from both the Fuchu area and an unpolluted area with e nvironmental factors different from those of the Fuchu area was performed. The results showed that the cause of renal dysfunction could not be explain ed by Cd-R alone, and difficult to clarify precisely the confounding factor s from the available data, it is concluded that deriving a safety level for foodstuffs using only the Cd-R level as a reference is not appropriate, (C ) 2000 Academic Press.