Urinary α1-Microglobulin, β2-Microglobulin, and Retinol-Binding Protein Levels in General Populations in Japan with References to Cadmium in Urine, Blood, and 24-Hour Food Duplicates

Possible cadmium (Cd) exposure-associated changes in urinary levels of low-molecular-weight proteins mere studied in nonsmoking and nondrinking female members of the general Japanese population (378 subjects with no known occupational heavy metal exposure) who lived at 19 study sites (all without any known environmental heavy metal pollution) in 13 prefectures throughout Japan. The external Cd dose was evaluated in terms of daily Cd intake via food (Cd-F), whereas Cd levels in blood (Cd-B) and urine (Cd-U) were taken as internal dose indicators. When the subjects were classified according to Cd-F into three groups with "low" (20.4 μg/day as a geometric mean of 97 women), "middle" (35.0 μg/day, 120 women) and "high" (67.0 μg/day, 66 women) exposure, both Cd-B and Cd-U increased in parallel with the changes in Cd-F. However, there were no dose-dependent changes in β2-microglobulin or retinol-binding protein levels in urine. α1-Microglobulin levels appeared to increase, but the distribution of the cases above the two cutoff levels of 9.6 and 15.8 μg/mg creatinine among the three Cd-F groups did not show any bias. Overall, it was concluded that there was no apparent Cd exposure-associated elevation in urinary low-molecular-weight protein levels in the study population.