Dr. Wasser and colleagues [1] suggest that a case of chronic active interstitial nephritis may have been attributable to previous ingestion of the nutritional supplement chromium picolinate. It appears that the authors are unaware of the major differences in the toxicology of hexavalent and trivalent forms of chromium. Hexavalent chromium is an unstable oxidizing compound that has induced acute tubular necrosis in episodes of industrial poisoning; long-term exposure in persons who work with chromium is associated with low-molecular-weight proteinuria [2]. In contrast, the nutritionally essential trivalent form of chromium is stable and essentially nontoxic on oral administration. A careful literature review failed to reveal any reports in which trivalent chromium, administered orally in any dose to animals or humans, induced renal toxicity or any lesion other than transient gastrointestinal irritation associated with massive bolus doses. Several reports indicate that high doses of parenteral trivalent chromium-for example, 2 mg/kg intraperitoneally daily for several weeks-can induce proximal tubular damage in rodents [3]; it is impossible to achieve oral absorption of such pathogenic doses because of the limited solubility and inefficient absorbability of trivalent complexes. In the judgment of the Environmental Protection Agency, daily ingestion of as much as 70 000 µg of trivalent chromium on a continuing basis would probably be safe [4]. Dr. Wasser's patient ingested 600 µg daily.

With regard to chromium picolinate specifically-a complex of trivalent chromium with the natural metabolite picolinic acid-a recent toxicology study found no histologic damage in rats who ingested up to 100 ppm chromium as chromium picolinate for 6 months [5]. Controlled clinical studies with chromium picolinate, done using daily doses of chromium as high as 1000 µg, found no perturbations of renal function or any other adverse effects, and no previous anecdotal reports have linked this nutrient to renal damage in more than 30 million person-years of use.