Tohoku J. Exp. Med., 2005, 205(3)

The Threshold Cadmium Level That Causes a Substantial Increase in β₂-Microglobulin in Urine of General Populations

MASAYUKI IKEDA, TAKAFUMI EZAKI, JIRO MORIGUCHI, YOSHINARI FUKUI, HIROHIKO UKAI, SATORU OKAMOTO and HARUHIKO SAKURAI¹

Kyoto Industrial Health Association, Kyoto, and ¹Occupational Health Research and Development Center, Japan Industrial Safety and Health Association, Tokyo, Japan

Cadmium (Cd) is a toxic element ubiquitous in the environment, and general populations have been exposed to this element primarily via foods. Thus, the critical level of non-occupational Cd exposure to cause any health effects among general populations is of public health as well as toxicological concern. The objectives of the present study were to examine the quantitative relationship between cadmium (Cd-U) and β₂-microglobulin in urine (β₂-MG-U) as a marker of exposure to Cd and as a marker of renal tubular dysfunction, respectively, and to identify a threshold Cd-U, if present, in causing a substantial increase in β₂-MG-U. Thus, paired data on geometric mean (GM) Cd-U_cr (i.e., Cd-U as corrected for creatinine [cr] concentration) and GM β₂-MG-U_cr (β₂-MG-U as corrected for cr) of residents in polluted as well as nonpolluted areas in Japan were retrieved in international and domestic sources. In practice, 245 cases of the data pairs were obtained in 51 articles published since 1975. Statistical analysis on ordinary scales disclosed that β₂-MG-U_cr increased markedly when Cd-U_cr exceeded a certain level. The relation between the two parameters after double-logarithmic conversion was in a shape of the letter J or a stick for ice hockey. Analysis for Cd-U_cr at the flexion point gave Cd-U_cr of 4 (on double logarithmic scales) or 7 μg / g cr (on ordinary scales). Cd-U_cr levels that correspond to a β₂-MG-U_cr of 1,000 μg / g cr were estimated to be 8-9 μg / g cr, by ordinary and logarithmic assumption as well as by the 3rd degree regression analysis. Thus, it is concluded that there is a threshold Cd-U_cr level that leads to a substantial increase in β₂-MG-U_cr, and that the threshold level is greater than 4 μg / g cr.

keywords —— cadmium; general population; Japan; β₂-microglobulin; urine

© 2005 Tohoku University Medical Press

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Address for reprints: Masayuki Ikeda, Kyoto Industrial Health Association, 67 Nishinokyo-Kitatsuboicho, Nakagyo-ku, Kyoto 604-8472, Japan.

e-mail: ikeda@kyotokojohokenkai.or.jp