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Trace Elements in Abiotic and Biotic Environments
chromium, or glucose tolerance factor, which is essential to glucose, protein, and fat
metabolism (Anderson 1981).
Without Cr 3+ in the diet, the body loses its ability to use sugars, proteins, and fat
properly, which may result in weight loss or decreased growth, improper function
of the nervous system, and a diabetic-like condition. Therefore, Cr 3+ compounds
have been used as dietary supplements and are beneficial if taken in recommended
dosages.
Chromium is a component of enzymes that controls glucose metabolism and
synthesis of fatty acids and cholesterol. Thus, its deficiency leads to severe impairment in glucose tolerance, which finally leads to diabetes and atherosclerotic disease
(ATSDR 2012a).
Tissue levels of Cr tend to decrease with age, which may be a factor in the increase
of adult-onset diabetes disease whose incidence rose more than sixfold during the
second half of the twentieth century. This increase may also mirror the loss of Cr
from diets, because of soil deficiency and the refinement of foods. Higher fat intake
also may inhibit Cr absorption. Even mild deficiencies of Cr can produce symptoms
other than problems in blood sugar metabolism, such as anxiety or fatigue. Abnormal
cholesterol metabolism and increased progress of atherosclerosis are associated with
Cr deficiency.
It is estimated that 25%–50% of the U.S. population being deficient in Cr because
of very low soil levels of Cr and the loss of this element from refined foods, especially sugar and flours. There are about 6 mg of Cr stored in the bodies of people who
live in the United States; tissue levels of people in other countries are usually higher,
and those higher levels tend to be associated with a lower incidence of diabetes and
atherosclerosis. There is less hardening of the arteries in Asians, who have five times
higher Cr tissue levels than Americans (Cefalu and Hu 2004).
Cr 6+ has been reported to be toxic and carcinogenic to humans owing to its oxidizing potential and easy permeation of biological membranes. International Agency
for Research on Cancer (IARC) has classified Cr 6+ in group 1 (human carcinogen)
and Cr metallic and Cr 3+ in group 3 (not classifiable as to its carcinogenicity to
humans) (IARC 2012a). However, Cr 3+ is an essential nutrient required for normal
energy metabolism. The Institute of Medicine of the National Research Council
determined an adequate intake (e.g., level typically consumed by healthy individuals) of 20–45 μg Cr 3+ /day for adolescents and adults (ATSDR 2012a). Estimated safe
and adequate daily dietary intakes for Cr is 50 ± 200 μg (WHO 2004). Data on daily
Cr intake in European countries are ranged from 22 to 146 μg, but most of them are
under 100 μg, whereas in the United States, the reported intake is between 23 and
62 μg (Van Cauwenbergh et al. 1996).
Chromium is present in the foodstuffs (Table 12.2), both as the inorganic form
and organic complexes. Most of Cr present in food is in the trivalent form, which is
an essential nutrient, when the toxic hexavalent form of Cr is not normally found in
food (Noël et al. 2003).
Controversy surrounding Cr supplementation is due, in part, to the substantial
variability in the results of studies that have evaluated the effects of Cr in patients
with or without diabetes. Results from some trials have indicated that Cr supplementation increases muscle gain and fat loss, associated with exercise and improves