Bioavailability of chromium(III)-supplements in rats and humans

Chromium(III) is long regarded as essential trace element but the biochemical function and even basic transport ways in the body are still unclear. For a more rational discussion on beneficial as well as toxic effects of Cr(III), we re-investigated the bioavailability of the most important oral Cr supplements by using radiolabeled compounds and whole-body-counting in rats and in the first time also in humans. The apparent absorption of Cr-51(III) from Cr-picolinate, Cr-nicotinate, Cr-phenylalaninate, Cr-proprionate, or Cr-chloride was generally low (0.04-0.24 %) in rats with slightly higher values for Cr-chloride and -phenylalaninate. Taking a fast urine excretion into account, the true absorption of Cr-51 was clearly higher for CrPic(3) (0.99 %), probably indicating a different uptake mechanism of this rather stable organic Cr complex. The bioavailability of CrPic(3) and Cr(d-Phen)(3), the leading compounds in actual investigations, was analysed also in human volunteer by intraindividual comparison. The apparent absorption (=Cr bioavailability) of Cr-51 from both compounds was substantially higher in humans (0.8-1 %) than in rats. Again, most of freshly absorbed CrPic(3) was excreted into the urine resulting in the same low whole-body retention after 7 days for both compounds. In summary, the bioavailability of Cr from pharmaceutical Cr compound is lower than hitherto assumed. Importantly, humans absorb Cr(III) clearly better than rats. The absorption mechanism of CrPic(3) seems to be different from ionic Cr(III) but, as only the same low amount of Cr is retained from this compound, it is also not more bioavailable than other Cr compounds.