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NEW YORK (Reuters Health) – Relatively low-level exposure to cadmium may increase the risk of end-stage renal disease (ESRD), Swedish researchers report in the November issue of the American Journal of Kidney Diseases.

In comments to Reuters Health, Dr. Carl-Gustaf Elinder of the Karolinska Institute, in Stockholm, noted that the methods of identifying the health effects of cadmium exposure have become much more sensitive in recent years. As a result, he said, "we have been able to unravel early effects in humans from cadmium at exposure levels which we and others previously considered to be safe."

Dr. Elinder's team calculated the incidence of renal replacement therapy (kidney dialysis or transplantation) in the relatively homogenous population of Kalmar County in southeast Sweden. Cadmium batteries have been produced in this area for more than 90 years. The researchers grouped the subjects according to high, moderate, low, or no cadmium exposure, based on present or previous employment at a cadmium battery plant or residence in a cadmium-polluted area near a plant.

The researchers found an exposure-response relationship between cadmium and the age-standardized rate ratio for renal replacement therapy. In the cadmium-exposed population the rate ratio was 1.8 compared with the unexposed group. The rate ratio was 2.3 for environmentally exposed women, which is not surprising, the team says, because women may absorb more ingested cadmium due to low iron stores.

"We did not expect the effect to be so evident, in particular not for the merely environmentally exposed groups," Dr. Elinder said.

"Because contact with ambient cadmium was not unusually high in the low- and moderate-exposure categories, [the] findings are somewhat alarming and of considerable general interest," the authors write in their report.

Dr. Elinder said his team has made every effort to identify possible bias and confounders, "but have not as yet been able to give an alternate explanation for our observation." Nonetheless, he emphasized that the finding needs to be confirmed by others before it can be claimed with any certainty that low-level environmental cadmium exposure increases the risk for ESRD.

"With regard to the occupationally exposed group, I am more confident about cadmium being an important contributing factor for ESRD," Dr. Elinder said.