Chromium: Is It Essential and Is It Safe?

Abstract

Elemental chromium (Cr) was discovered in crocoite, a mineral with a deep-orange red color, by Vaquelin in 1798 [1]. Schwartz and Mertz [2] in 1959 were the first to report Cr was an essential element in rats while in 1977 Jeejebhoy et al. [3] showed it was essential in humans. Many research studies were conducted with Cr over the years [4] but the main focus was its relationship with diabetes mellitus [5]. While the evidence supporting an anti-diabetic role for Cr appeared strong it was still far from definitive [6]. The two main forms of chromium are the trivalent CrIII (chromium III) and the hexavalent form CrVI (chromium VI). Of these, CrIII is the most stable oxidation state found in living organisms but unable to cross cell wall membranes easily [7]. Complexing with certain organic ligands such as picolinic acid, however, allowed CrIII to be readily absorbed by cell membranes [8]. A recent paper by Doddigarta and co-workers [9] showed that male Wistar rats fed a high carbohydrate diet supplemented with chromium picolinate (CrPlc) and melatonin, given individually or in combination, prevented the development of insulin resistance and type 2 diabetes. A series of studies by Anderson’s group in the 1990’s [10-12] used a low-Cr diet when feeding rats 55% sucrose, 15% lard, 25% casein plus vitamins, and minerals. A close examination of these studies by Bona et al. [13] questioned whether such diets were low in chromium as based on their calculations the rats were provided with 10 times higher levels of Cr per kg body weight than recommended for humans. According to National Academy of Science an adequate intake (AI) for chromium is 35 µg/day for men and 25 µg/day for women [14]. Using carefully controlled metal-free conditions (including plastic cages); Bona et al. [13] fed male Zucker lean rats over 6 months an AIN-93 G diet supplemented with 200 µg and 1000 µg Cr/kg. None of the diets, including those supplemented with Cr, had any effect on body composition, glucose metabolism or insulin sensitivity. These results raised serious concerns as to whether CrIII was actually essential. A review of previous papers by Yoshida et al. [15] also questioned whether Cr was an essential trace element. The amount of Cr provided to experimental animals far exceeded the daily human intake of 20- 80 µg/day and was closer to a pharmacological dose. Based on these results they also questioned whether Cr was indeed an essential trace element. After an extensive of the literature, the European Food Safety Authority determined that Cr should no longer be considered essential for humans or animals [16].